System bus - why is it needed? Types, purpose and operation of tires. System buses include
Hello, dear readers of the blog site. Very often on the Internet you can find a lot of all kinds of computer terminology, in particular, such a concept as “System bus”. But few people know what exactly this computer term means. I think today's article will help clarify things.
The system bus (bus) includes a data, address and control bus. Each of them transmits its own information: on the data bus - data, addresses - respectively, the address (of devices and memory cells), control - control signals for devices. But now we will not delve into the jungle of the theory of computer architecture organization; we will leave this to university students. Physically, the highway is presented in the form of (contacts) on the motherboard.
It is no coincidence that I pointed out the inscription “FSB” in the photo for this article. The point is that connecting the processor to the chipset The answer is the FSB bus, which stands for "Front-side bus" - that is, "front" or "system". And, which is usually used when overclocking a processor, for example.
There are several varieties of the FSB bus, for example, on motherboards with Intel processors, the FSB bus usually has a variety of QPB, in which data is transferred 4 times per clock cycle. If we are talking about AMD processors, then data is transferred 2 times per clock cycle, and the type of bus is called EV6. And in the latest AMD CPU models there is no FSB at all, its role is played by the latest HyperTransport.
So, data is transferred between and the central processor at a frequency exceeding the FSB bus frequency by 4 times. Why only 4 times, see paragraph above. It turns out that if the box indicates 1600 MHz (effective frequency), in reality the frequency will be 400 MHz (actual). In the future, when we talk about overclocking the processor (in the following articles), you will learn why you need to pay attention to this parameter. For now, just remember, the higher the frequency, the better.
By the way, the inscription "O.C." means literally “overclocking”, this is an abbreviation for English. Overclock, that is, this is the maximum possible system bus frequency that the motherboard supports. The system bus can safely operate at a frequency significantly lower than that indicated on the packaging, but not higher than it.
The second parameter characterizing the system bus is. This is the amount of information (data) that it can pass through itself in one second. It is measured in Bit/s. Bandwidth can be calculated independently using a very simple formula: bus frequency (FSB) * bus width. You already know about the first multiplier, the second multiplier corresponds to the processor bit size - remember, x64, x86(32)? All modern processors are already 64-bit.
So, we substitute our data into the formula, the result is: 1600 * 64 = 102,400 MBit/s = 100 GBit/s = 12.5 GBit/s. This is the bandwidth of the highway between the chipset and the processor, or more precisely, between the northbridge and the processor. That is system, FSB, processor buses - all these are synonyms. All connectors on the motherboard - video card, hard drive, RAM "communicate" with each other only through highways. But FSB is not the only one on the motherboard, although it is certainly the most important.
As can be seen from the figure, the Front-side bus (the boldest line) essentially connects only the processor and the chipset, and from the chipset there are several different buses in other directions: PCI, video adapter, RAM, USB. And it’s not at all a fact that the operating frequencies of these subbuses should be equal to or a multiple of the FSB frequency; no, they can be completely different. However, in modern processors the RAM controller is often moved from the northbridge to the processor itself, in which case it turns out that there is no separate RAM bus; all data between the processor and RAM is transferred directly via the FSB at a frequency equal to the FSB frequency.
That's all for now, thanks.
Serves for the exchange of commands and data between computer components located on the mat. board The control panel is connected to the bus through controllers (open architecture). transmission of information via system. The bus is carried out in cycles.
Syst. tire includes:
Code data bus for //-th transfer of all bits of the numeric code (machine word) of the operand from RAM to MPP and back (64 bits)
RAM cell address code bus (32 bits)
Code bus of instructions (commands and control signals, pulses) to all computer blocks (32 bits)
Power bus for connecting computer units to the power supply system
Syst. The bus provides 3 directions of information transfer: - between MP and RAM; -between the MP and the device controller; -between RAM and External Devices (VZU and PU, in direct memory access mode)
All devices are connected to the system. bus through controllers - devices that ensure interaction between the computer and the system. tires.
To free the MP from managing the exchange of information between RAM and the VU, the Direct Memory Access (DMA - direct memory access) mode is provided.
System characteristics buses: number of devices served by it and bandwidth, i.e. Max. possible speed of information transfer.
The bus capacity depends on:
Bus capacity (or width) - number of bits, cat. M.B. transmitted over the bus simultaneously (there are 8,16,32, and 64-bit buses);
Bus clock frequency - frequency, s cat. bits of information are transmitted over the bus.
Main characteristics of tires:
PCI (Peripheral Component Interconnect) is the most common system bus. The bus speed does not depend on the number of connected devices. Supports the following modes:
- Plug and Play (PnP) – automatic detection and configuration of a device connected to the bus;
- Bus Mastering– mode of sole control of the bus by any device connected to the bus, which allows you to quickly transfer data across the bus and release it.
AGP (Accelerated Graphics Port) is the highway between the video card and RAM. Developed because the PCI bus parameters do not meet the performance requirements of video adapters. The bus operates at a higher frequency, which speeds up the operation of the computer's graphics subsystem.
Main characteristics of tiresLecture 5
18. Computer memory and its characteristics and purpose. Pzu, ozu, vzu. Organization and physical representation of data on a computer.
Permanent and operational memory.
Memory in a computer consists of a sequence of cells, each of which contains the value of the 1st byte and has its own number (address) through which its contents are accessed. All data in the computer is stored in binary form (0,1).
The memory is characterized by 2 parameters:
Memory capacity - size in bytes available for storing information
Access time to memory cells - the average time interval during the cat. the required memory cell is located and data is extracted from it.
Random access memory (RAM; RAM – Random Access Memory) is designed for online recording, storage and reading of information (programs and data) directly involved in the information and computing process performed by the computer in the current period of time. After turning off the computer's power, the information in RAM is destroyed. (Computers based on Intel Pentium processors use 32-bit addressing. That is, the number of addresses is 2 32, that is, the possible address space is 4.3 GB. Access time is 0.005-0.02 μs. 1 s = 10 6 μs.
Read-only memory (ROM; ROM - Read Only Memory) stores unchangeable (permanent) information: programs executed during system boot, and permanent computer parameters. When the computer is turned on, there is no data in its RAM, since RAM does not save data after the computer is turned off. But the MP needs commands, including immediately after switching on. Therefore, the MP applies to a special starting address, which is always known to him, for his first team. This address is from ROM. The main purpose of programs from ROM is to check the composition and performance of the system and ensure interaction with the keyboard, monitor, hard and floppy disks. Usually you cannot change ROM information. ROM volume 128-256 KB, access time 0.035-0.1 μs. Since ROM is small in size but has longer access times than RAM, at startup the entire contents of ROM are read into a specially allocated area of RAM.
Non-volatile memory CMOS RAM (Complementary Metal-Oxide Semiconductor RAM), which stores data about the hardware configuration of the computer: devices connected to the computer and their parameters, boot parameters, login password, current time and date. The CMOS RAM memory is powered by a battery. If the battery power runs out, the settings stored in the CMOS RAM are reset and the computer uses the default settings.
ROM and CMOS RAM memory make up the basic input-output system (BIOS - Basic Input-Output System).
External storage devices. VSD for long-term storage and transportation of information. VZU interact with the system. bus through VZU (KVZU) controllers. KVZU provide the interface between the VZU and the system. buses in direct memory access mode, i.e. without the participation of the MP. INTERFACE is a set of connections with unified signals and equipment designed for data exchange between devices of a computer system.
VZU can be divided according to the criterion of transportation into PORTABLE and STATIONARY. Portable VSDs consist of media connected to an I/O port (usually USB), (flash memory) or media and a drive (HDD drives, CD and DVD drives). In stationary VSDs, the media and drive are combined into a single device (HDD). Stationary VSDs are designed to store information inside a computer.
Before first use or in case of failures, the VSD must be FORMATTED - write service information to the media.
Main Technical Characteristics of the VZU
Information capacity determines the largest number of units. data, the cat can simultaneously store in the VRAM (depending on the area of the storage medium and the recording density.)
Recording density is the number of bits of information recorded on a unit of media surface. A distinction is made between longitudinal density (bit/mm) and transverse density.//
Access time - the time interval from the moment of the request (reading or writing) to the moment the block is issued (including the time of searching for infection on the media and the time of reading or writing.)
The data transfer rate determines the amount of data read or written per unit of time and depends on the speed of the media, recording density, number of channels, etc.
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It was eight-bit, i.e. it could simultaneously transmit 8 bits. The system buses of modern PCs, for example, Pentiurr IV, are 64-bit.
The bus throughput is determined by the number of bytes of information transmitted over the bus per second. To determine the bus bandwidth, it is necessary to multiply the bus clock frequency by its bit width. For example, for a 16-bit ISA bus, the bandwidth is defined as follows:
(16 bits * 8.33 MHz): 8 = 16.66 MB/s.
When calculating the throughput of, for example, the AGP bus, you should take into account its operating mode: by doubling the clock frequency of the video processor and changing the data transfer protocol, it was possible to increase the bus throughput by two (2x mode) or four times (4* mode), which is equivalent to increasing the bus clock frequency by the corresponding number of times (up to 133 and 266 MHz, respectively).
External devices are connected to the buses through an interface (Interface - pairing), which is a set of various characteristics of a PC peripheral device that determine the organization of information exchange between it and the central processor.
Such characteristics include electrical and timing parameters, a set of control signals, a data exchange protocol and design features of the connection. Data exchange between PC components is only possible if the interfaces of these components are compatible.
PC bus standards
The principle of IBM compatibility implies standardization of the interfaces of individual PC components, which, in turn, determines the flexibility of the system as a whole, i.e. the ability to change the system configuration and connect various peripheral devices as necessary. In case of interface incompatibility, controllers are used. In addition, flexibility and unification of the system are achieved through the introduction of intermediate standard interfaces, such as serial and parallel data transfer interfaces. These interfaces are necessary for the operation of the most important peripheral input and output devices.
The system bus is designed to exchange information between the CPU, memory and other devices included in the system.
System buses include:
GTL, which has a bit depth of 64 bits, a clock frequency of 66, 100 and 133 MHz;
EV6, the specification of which allows you to increase its clock frequency to 377 MHz.
I/O buses are being improved in line with the development of PC peripherals. In table 2.5 shows the characteristics of some input/output buses.
ISA bus was considered a PC standard for many years, but is still retained in some PCs today along with the modern PCI bus. Intel, together with Microsoft, has developed a strategy to phase out the ISA bus. Initially, it is planned to eliminate ISA connectors on the motherboard, and subsequently eliminate ISA slots and connect disk drives, mice, keyboards, scanners to the USB bus, and hard drives, CD-ROM, DVD-ROM drives to the NEC 1394 bus. However, the presence of a huge A couple of PCs with an ISA bus and corresponding components suggest that the 16-bit ISA bus will be in demand for some time to come.
EISA bus became a further development of the ISA bus in the direction of increasing system performance and compatibility of its components. The bus is not widely used due to its high cost and bandwidth, which is inferior to the VESA bus that appeared on the market.
VESA bus, or VLB, designed to connect the CPU with fast peripheral devices and is an extension of the ISA bus for exchanging video data. When the CPU 80486 processor dominated the computer market, the VLB bus was quite popular, but has now been replaced by the more powerful PCI bus.
PCI bus was developed by Intel for the Pentium processor and is a completely new bus. The fundamental principle underlying the PCI bus is the use of so-called bridges, which communicate between the PCI bus and other types of buses. The PCI bus implements the Bus Mastering principle, which implies the ability of an external device to control the bus when sending data (without the participation of the CPU).
During information transfer, a device that supports Bus Mastering takes over the bus and becomes the master. In this case, the central processor is freed up to perform other tasks while data is being transferred. In modern motherboards, the PCI bus clock frequency is set as half the system bus clock frequency, i.e. with a system bus clock frequency of 66 MHz, the PCI bus will operate at a frequency of 33 MHz. Currently, the PCI bus has become the de facto standard among I/O buses. In Fig. 2.6 shows the PCI bus architecture
AGP bus— high-speed local input/output bus, designed exclusively for the needs of the video system. It connects the video adapter (ZO accelerator) with the PC system memory. The AGP bus was designed based on the PCI bus architecture, so it is also 32-bit. However, at the same time, it has additional opportunities to increase throughput, in particular, through the use of higher clock frequencies.
If in the standard version the 32-bit PCI bus has a clock frequency of 33 MHz, which provides a theoretical PCI throughput of 33 x 32 = 1056 Mbit / s = 132 MB / s, then the AGP bus is clocked by a signal with a frequency of 66 MHz, so its throughput is 1x mode is 66 x 32 = 264 MB/s; in 2x mode, the equivalent clock frequency is 132 MHz, and the bandwidth is 528 MB/s; in 4x mode the throughput is about 1 GB/s.
USB bus was developed by leaders in the computer and telecommunications industry Compaq, DEC, IBM, Intel, Microsoft for connecting peripheral devices outside the PC case. The speed of information exchange via the USB bus is 12 Mbit/s or 15 MB/s. To computers equipped with a USB bus, you can connect peripheral devices such as a keyboard, mouse, joystick, printer without turning off the power. The TJSB bus supports Plug & Play technology.
When a peripheral device is connected, it is configured automatically. All peripheral devices must be equipped with USB connectors and connected to the PC through a separate remote unit called a USB hub, or hub, with which up to 127 peripheral devices can be connected to the PC. The architecture of the USB bus is shown in Fig. 2.7.
SCSI bus(Small Computer System Interface) provides data transfer speeds of up to 320 MB/s and provides for connecting up to eight devices to one adapter: hard drives, CD-ROM drives, scanners, photo and video cameras. A distinctive feature of the SCSI bus is that it is a cable loop. The SCSI bus is connected to the PC buses (ISA or PCI) through a Host Adapter. Each device connected to the bus has its own identification number (ID). Any device connected to the SCSI bus can initiate communication with another device.
In Fig. Figure 2.8 shows the connection of peripheral devices to a PC using the SCSI bus. There is a wide range of SCSI versions, from the original SCSI I, which provides a maximum throughput of 5 MB/s, to the Ultra 320 version, which provides a maximum throughput of 320 MB/s. The IEEE 1394 bus can compete with the SCSI bus.
IEEE 1394 bus is a high-speed local serial bus standard developed by Apple and Texas Instruments. The IEEE 1394 bus is designed for the exchange of digital information between PCs and other electronic devices, especially for connecting hard drives and audio and video processing devices, as well as multimedia applications. It is capable of transmitting data at speeds of up to 1600 Mbit/s and working simultaneously with several devices transmitting data at different speeds, just like SCSI. Like USB, the IEEE 1394 bus fully supports Plug & Play technology, including the ability to install components without turning off the power to the PC.
Almost any device capable of working with SCSI can be connected to a computer via the IEEE 1394 interface. These include all types of disk drives, including hard drives, optical drives, CD-ROMs, DVDs, digital video cameras, tape recorders, and many other peripherals. Thanks to such wide capabilities, this bus has become the most promising for combining a computer with consumer electronics. IEEE 1394 adapters for the PCI bus are currently being produced.
Questions for students to take notes:
1. Bus definition
2. Purpose of tires
3. Bus architecture
4. The concept of bus width.
5. The concept of bus bandwidth
6. PC bus interface
7. Principle of IBM compatibility
8. Types of tires and their characteristics (fill out the table)
| Types of tires | Tire characteristics | ||||
| Speed | Purpose | Peculiarities | Advantages | Flaws | |
11 System bus, system bus operating modes, programmable system devices
Buses are sets of conductors through which signals are exchanged between the internal devices of a computer;
System bus - designed to transfer information between the processor and other electronic components of the computer. The system bus is used to address devices and exchange special service signals. Simplified, the system bus can be represented as a set of signal lines, united by purpose (data, addresses, control). The system bus is a set of electrical signal conductors and a system of protocols for connecting devices using these conductors. The type and characteristics of information transfer protocols over the system bus determine the speed of information transfer between individual devices on the motherboard. System buses of personal computers are standardized both in terms of the number of contacts and bit depth (the number of conductors used for simultaneous data transfer), and in the protocols for communication between devices through conductors. The system bus connects all computer devices into a single whole and ensures their interaction, mutual control and operation with the central processor. Personal computers use system buses of the ISA, EISA, VLB and PSI standards. Nowadays, only the PCI bus is used; of course, you can still find ISA, but it is too slow compared to PCI, so I no longer produce it.
18 Computer video system. Work principles. Areas of use
Video card (video adapter) Together with the monitor, the video card forms the video subsystem of a personal computer. The video card has not always been a PC component. At the dawn of the development of personal computing technology, in the general area of RAM there was a small dedicated screen memory area into which the processor entered image data. A special screen controller read data on the brightness of individual points of the screen from the memory cells of this area and, in accordance with them, controlled the scan of the horizontal beam of the monitor's electron gun. With the transition from black-and-white monitors to color ones and with an increase in screen resolution (the number of pixels vertically and horizontally), the video memory area became insufficient to store graphic data, and the processor could no longer cope with constructing and updating the image. It was then that all operations related to screen control were separated into a separate block, called the video adapter. Physically, the video adapter is designed as a separate daughter card, which is inserted into one of the slots on the motherboard and is called a video card. The video adapter took over the functions of the video controller, video processor and video memory. During the existence of personal computers, several video adapter standards have changed: MDA (monochrome); CGA (4 colors); EGA (16 colors); VGA (256 colors). Currently, SVGA video adapters are used, providing optional reproduction of up to 16.7 million colors with the ability to arbitrarily select screen resolution from a standard range of values (640x480, 800x600, 1024x768, 1152x864; 1280x1024 pixels and beyond). Screen resolution is one of the most important parameters of the video subsystem. The higher it is, the more information can be displayed on the screen, but the smaller the size of each individual dot and, thus, the smaller the apparent size of the image elements. Using an inflated resolution on a small monitor results in image elements becoming illegible and working with documents and programs causes visual fatigue. Using a low resolution results in large image elements, but there are very few of them on the screen. If a program has a complex control system and a large number of screen elements, they do not completely fit on the screen. This leads to decreased productivity and ineffective work. Color resolution (color depth) determines the number of different shades that a single point on the screen can take on. The maximum possible color resolution depends on the properties of the video adapter and, first of all, on the amount of video memory installed on it. In addition, it depends on the set screen resolution. With a high screen resolution, each pixel in the image has to be allocated less space in video memory, so color information is forced to be more limited. The minimum requirement for color depth today is 256 colors, although most programs require at least 65 thousand colors (High Color mode). The most comfortable work is achieved with a color depth of 16.7 million colors (sharp True Color). Working in full color True Co1or mode with high screen resolution requires significant amounts of video memory. Modern video adapters are also capable of performing image processing functions, reducing the load on the central processor at the cost of additional video memory costs. Until recently, video adapters with a memory capacity of 2-4 MB were considered typical, but today a capacity of 16 MB is considered common. Video acceleration is one of the properties of a video adapter, which lies in the fact that some of the operations for constructing images can occur without performing mathematical calculations in the main computer processor, but purely in hardware - by converting data in video accelerator chips. Video accelerators can be included in the video adapter (in such cases the video card is said to have hardware acceleration functions), but can be supplied as a separate board installed on the motherboard and connected to the video adapter. There are two types of video accelerators - flat (2D) and three-dimensional (3D) graphics accelerators. The former are most effective for working with application programs (usually office applications) and are optimized for the Windows operating system, while the latter are focused on multimedia entertainment programs, primarily computer games and professional 3D graphics processing programs. Typically, in these cases, different mathematical principles are used to automate graphic operations, but there are accelerators that have both two-dimensional and three-dimensional acceleration functions.
An integral part (although the display was first implemented on some second-generation computers, for example, on MIR-2, a very interesting domestic development in many respects). Figure 3.1 - Computer bus architecture To obtain a stable image on the monitor screen, it must be stored somewhere. That's what video memory is for. First, the contents of the video memory are generated by the computer, and...
User. Using the keyboard, they control the computer system, and using the monitor, they receive feedback from it. Operating principle. The keyboard is one of the standard features of a personal computer. Its main functions do not require support from special system programs (drivers). The necessary software to start working with a computer is already available in the ROM chip in...
Buses, as you know, are used to transfer data from the central processor to other devices of a personal computer. In order to coordinate data transfer to individual components operating at their own frequency, a chipset is used - a set of controllers structurally combined into North and South bridges. The North Bridge is responsible for exchanging information with RAM and the video system, the South Bridge is responsible for the functioning of other devices connected through the appropriate connectors - hard drives, optical drives, as well as devices located on the motherboard (built-in audio system, network device, etc.), and for external devices - keyboard, mouse, etc.
The system board diagram is shown below.
To connect the processor with bridges, the FSB (Front Side Bus) bus is used (the most commonly used currently are Hyper-Transport and SCI), the north bridge (sometimes called the system controller) allows the most powerful devices to function - the video adapter using the PCI Express 16x bus and RAM memory via the memory bus. The South Bridge ensures the operation of lower-speed devices connected using expansion cards (audio cards, network cards, video cards, etc.) via PCI buses and the PCI Express bus, optical drives and hard drives via ATA buses (formerly called IDE, now called PATA (Parallel ATA) and more modern SATA buses Even slower devices are connected to the south bridge via the LPC bus - a BIOS chip, a multicontroller for communicating with external devices via serial and parallel ports - keyboard, mouse, printer, etc.
Note that in the most modern computers, the functions of the north bridge are performed by the central processor (Intel Nehalem, AMD Sledgehammer).
A computer has several buses through which data is transferred. The main bus is between the central processor and the Northbridge. You can read about the frequency of this bus in the section on processors. The next bus is between the processor and RAM (previously it was between the North Bridge and RAM). You can learn about its characteristics from the section on RAM. The buses that lead to expansion cards, which we will describe below, remain unexamined.
The data bus carries data directly, and the more lines it has, the more data can be transferred in one clock cycle, so the number of lines is constantly increasing. To transfer data inside the computer, a special bus is used, which consists of three parts, through which data, addresses, control signals, as well as grounding, voltage, etc. are transmitted. That is, practically data is transferred in three parts: address bus, data bus and bus management. The number of address bus lines determines the maximum address space where data can be sent, mainly to RAM. The 8086 processor had 20 address lines and could address 2 20 = 1 megabyte of memory, the 286 had 24 lines (2 24 = 16 megabytes), the 386 had 32 lines (2 32 = 4 gigabytes), modern computers have more than 32 lines. That is, the more lines in the address bus, the more RAM the motherboard supports.
The data bus transmits data directly and the more lines it has, the more data can be transferred in one clock cycle. Therefore, the number of lines is constantly increasing, starting from 8 in the first computers to 32 in Pentium systems.
Through the motherboard connectors, through the inserted cards, information is transmitted to/from the processor to external devices in relation to the motherboard. Naturally, these connectors cannot transmit more data than is supported by the internal system bus, and usually less, depending on the type of bus with which the expansion cards work. There are several types of buses and, accordingly, connectors: ISA, EISA, PCI and others. The latest computer models mainly use the more powerful PCI-E bus. But quite a few devices still run on less efficient buses. Therefore, modern motherboards have up to 5 different buses and their corresponding connectors.
Let's take a closer look at the available tires.
ISA bus(Industry Standard Architecture) appeared a long time ago and was a standard for a long time. Now it is hopelessly outdated. In total, the first XT models had 8 data lines, which allowed for byte transfer, 20 address lines for addressing up to 1 megabyte of memory, and another 34 lines for other purposes. When switching to the RS AT model, another 36 lines were added, including 8 for data and 4 for address. 8-bit was used in PC XT, had 62 contacts and allowed addressing 1 MB of memory. Next came the 16-bit (sometimes called AT BUS), operating at a frequency of 8 MHz with a speed of 16 Mb/sec, allowing you to address up to 16 Megabytes. It consists of two parts, the first of which corresponds to the 8-bit ISA bus slot. The additional 8 bits are used for additional I/O addresses and contain 36 slots (so you can install 8-bit cards in a 16-bit slot). However, this device had a clock frequency of 8.33 MHz and worked slowly, so other buses appeared.
Currently, the Plug-an d-Play (PnP) standard works, which allows configuration to be performed automatically when installing a new device. In this case, the system itself determines the type of device, I/O port address, interrupt number and direct memory access (DMA) channel. However, older tires have difficulty using this standard. Thus, the ISA bus was developed before the advent of PnP. Therefore, not all devices that connect to this bus can be automatically configured. To get out of the current situation, Windows 9x has a list of devices that can be connected to the computer and which install themselves.
The ISA bus has the following restrictions:
The presence of a 16-bit bus, that is, the ability to simultaneously send two bytes;
Maximum clock frequency 8.33 MHz;
No sharing of interrupts and DMA channels across multiple cards in different slots;
Inability to programmatically disable the card in the event of a device conflict;
Lack of software control of I/O port addresses, interrupt lines and direct access channels.
To install an ISA card on an EISA bus, you typically need to have a configuration file to run the EISA bus configuration utility, which will then allocate resources to the card.
When installing a new device, you need it to be physically and logically compatible. Physical alignment means that the type of connector and the number of pins on the plug and connector must match each other. Logical alignment means that the contacts through which voltage is supplied, where there is grounding, etc. must be clearly defined. In this case, the signal sent over one contact must be identified by the receiving device as a data transfer signal, and not as a control signal. All this is determined by the tire standard.
This standard is usually established by the manufacturer, which has begun mass production of new devices. These include the EIDE bus for connecting hard drives, serial and parallel ports, a bus for outputting graphic images, a bus for connecting expansion cards, a USB bus, IrDA, etc., which have their own standards. However, in practice, the term bus often refers to the bus to which the expansion card is connected. Therefore, in this book, from now on, the bus will simply be called the PCI bus, VESA bus, etc. In conclusion, we note that the first computer buses were called Multibus1. They were produced in two versions: PC/XT bus and PC/AT bus and had 7 lines for hardware interrupts. They were later replaced by the ISA bus.
MCA bus(Microchannel) appeared in 1987, developed by IBM and installed on the PS/2 ISA computer. There are two types: 16-bit and 32-bit. The 32-bit operates at a frequency of 10 MHz, with a data transfer rate of up to 20 Mb/s, and allows you to address up to 4 gigabytes. The expansion card could be independently recognized and automatically configured by the computer. The main disadvantage is the incompatibility with the ISA bus, for which the main devices were developed, so this architecture is not widely used.
TireEISA(Extended ISA - extended ISA) was released by a group of companies competing with IBM in 1988, since the MCA bus had a closed description and could only be used by IBM, and was also already outdated. The advantages include its compatibility with the ISA connector due to the arrangement of the connectors in two layers, on one ISA, on the second - EISA. This bus is 32-bit, operates at a frequency of 8.33 MHz and provides a maximum data transfer speed of up to 33 Mb/s. The configuration is set programmatically, not using switches.
To prevent the two layers from being shorted when installing a card that requires an ISA connector, the connector has a plug that prevents connection to the bottom contacts. The EISA card contains a cutout in the place of the plug that allows you to bypass this plug.
Due to its high cost, the EISA bus was not widely used in personal computers, but was used in workstations and servers.
Tire SCSI(Small Computer System Interface - small system computer interface) is designed to connect large arrays of devices to the bus, such as hard drives, optical drives, tape drives, printers, etc. Therefore, it is mainly used in server computers or computers with a RAID system. It is practically not used in home computers.
SCSI-1 appeared in 1986, had 8 data lines, each device with its own number, with the adapter assigned number 7. The remaining devices have a number from 0 to 6, and the number is set manually on the back of the connected device or using jumpers. Devices on the bus can exchange information with each other without the participation of an adapter, which in this case determines who can transfer data to whom. At the same time, when information passes through him, he takes part in it. Bus frequency is 5 MHz, maximum number of connected devices is 8.
Fast SCSI appeared in 1991 and had 8 data lines, as well as an improved cable connector. Bus frequency – 10 MHz, bandwidth – 10 MB/sec, maximum number of connected devices – 8.
Wide SCSI had 16 lines for data transmission, bus frequency – 10 MHz, bandwidth – 20 MB/sec, maximum number of connected devices – 16.
Ultra SCSI appeared in 1992, had 8 lines for data transmission, bus frequency - 20 MHz, bandwidth - 20 MB/sec, maximum number of connected devices - 4-8.
Ultra Wide SCSI had 16 lines for data transmission, bus frequency - 20 MHz, bandwidth - 40 MB/sec, maximum number of connected devices - 4 - 16.
Ultra 2 SCSI appeared in 1997, had 8 lines for data transmission, bus frequency – 10 MHz, bandwidth – 40 MB/sec, maximum number of connected devices – 8.
Ultra 2 Wide SCSI had 16 lines for data transmission, bus frequency – 40 MHz, bandwidth – 80 MB/sec, maximum number of connected devices – 16.
Ultra 3 SCSI had 16 lines for data transmission, bus frequency – 40 MHz, bandwidth – 160 MB/sec, maximum number of connected devices – 16.
Ultra -320 SCSI had 16 lines for data transmission, bus frequency – 80 MHz, bandwidth – 320 MB/sec, maximum number of connected devices – 16.
Ultra -640 SCSI appeared in 2003, had 16 lines for data transmission, bus frequency – 160 MHz, bandwidth – 640 MB/sec, maximum number of connected devices – 16.
Subsequently, technology began to develop SAS(Serial Attached SCSI) for working with hard drives and tape drives. You can connect SATA devices to a SAS connector, but not vice versa. Provides throughput of 1.5, 3.0, 6.0 Gbit/s, 12 Gbit/s expected. Allows you to connect not only 3.5-inch drives, but also 2.5-inch drives.
The adapter itself is located on the motherboard (like a Mac) or on an expansion card. The card is inserted into the PCI slot. The SCSI device cable on Mac computers has a female connector with a DB25 connector, the same as the parallel port. If you accidentally connect it to a printer or parallel port on a computer, or, conversely, connect a printer cable to a SCSI device, the chips of the device to which they are connected may burn out.
When transmitting data over a cable, a so-called “standing wave” may arise in it. To prevent it from happening, a special plug is used to extinguish it. Moreover, this plug should be one and located at the end of the cable. SCSI devices can have two connectors, one of which is connected to the SCSI bus, and the second, if it is at the end of the cable, must have a plug. If there are two stubs on two devices on a line, they may prevent each other from performing their role.
The SCSI bus works somewhat differently with hard drives than other standards, considering the disk not as records having heads, cylinders, sectors, but as a sequence of logical records. When the SCSI adapter receives information from the CPU about a record at a specific address for the hard drive, the SCSI adapter translates it into a logical record number. As a result, if the hard drive is installed in place of any SCSI device of this adapter, it will work, but if installed in other adapters, the system may not read the data about converting the disk to the new structure, all information on the disk will be destroyed.
Other devices (optical drives, Iomega) have special drivers that allow them to be freely moved from one system to another. You can use both devices connected to a SCSI adapter and EIDE at the same time on one computer.
SCSI devices require a termination at the end of the cable that connects them. As a rule, it is installed at the factory on each device. Therefore, when installing all devices except the last one, you need to remove them. If devices connected to the SCSI bus do not support the Plug & Play standard, then the device number must be set on them using jumpers. Keep in mind that some adapters require devices numbered 0 and 1 to be hard drives.
EIDE bus intended for connecting hard drives and optical drives. Also called as ATA or RATA(parallel ATA). Now it is being replaced by the SATA bus, but, nevertheless, it is also installed on modern boards, since several optical drives can be connected to it (two for each connector). This is discussed in more detail in the section on hard drives. The first disk drives were connected to the computer using cards that contained a disk controller. Over time, as chip sizes decreased, the controller began to be installed on the hard drive, and the floppy drive controller on the motherboard, so it became possible to connect hard drives directly through the connector on the motherboard.
This is how the IDE bus appeared, which is part of the ISA bus, which is connected to a special connector (in modern devices there are two connectors) on the motherboard. First, a bus standard called ATA was developed, then ATAPI, which made it possible to work with optical drives. Over time, an expanded version of EIDE appeared with the ATA standard and subsequently an extension of the standard - ATAPI. If there are more devices connected to the EIDE connector than the computer can support, then you need to install a special card to which you can connect several more devices.
The first standards used hard drives connected to the board using special cards on which the controller was located, to the ISA bus. Over time, the size of electronic components has shrunk and they began to be installed on the hard drive itself. Next, drives began to be connected to the board via an IDE connector, then two connectors appeared, and up to two devices could be connected to each connector, performance increased, addressing of logical blocks was introduced, it became possible to connect optical drives, and all this was supported by the EIDE standard, which works with a clock frequency of 8.33 MHz. The first devices worked with the ATA standard, and then ATAPI, which allowed connection to an optical device channel. Since it became possible to transmit 2 bytes simultaneously over the channel in one clock cycle, the transfer speed over the same lines reached 16.6 MB/sec. Over time, data was transferred in one clock cycle not only when moving from high to low voltage, but also when moving from low to high. This standard is called Ultra ATA or ATA33, as it allows data transfer at a speed of 33.3 MB/sec.
Later, the ATA66 standard appeared, in which the clock frequency in the channel increased to 16.7 MHz and data transfer occurs at a speed of 66.7 MB/sec. The cable for connecting the hard drive to the motherboard is different and contains 80 wires instead of 40, as was the case with previous standards. There are 40 wires used to connect devices to this cable. If you connect a device capable of operating in ATA33 to this channel, or a device operating with the ATA66 standard to the ATA33 bus, the device will operate at a speed of 33.3 MB/sec. In some boards, ATA and its extension ATAPI allows you to connect devices with different speeds to the same bus without reducing performance, but it is better to separate them into different channels.
The cable for working with the IDE ATA (AT-Bus) standard is 16-bit, has 40 cores. The XT IDE cable (8 bit) also has 40 cores, but is not ATA compatible, meaning it cannot be used for the IDE standard.
There are two DMA channel operating modes: Singleword and Multiword. Singleword DMA has mode 0, which operates at a speed of 2.08 MB/sec, mode 1 – 4.16, mode 2 – 8.33, and Multiword DMA has mode 0, which operates at a speed of 4.12, mode 1 – 13.3, mode 2 – 16.6 MB/sec . Ultra DMA mode has mode 0, operating at speed – 16.6, mode 1 – 25, 2 – 33.
In addition, there are other PIO modes, from 0 and higher, and the higher the number, the faster the bus runs.
ATA-2 mode operates in PIO Mode 3 multiword DMA Mode 1, supports LBA and CHS. Fast ATA-2 supports Multiword DMA mode 2 and PIO mode 4. ATA3 is an extension of ATA2 with Smart, that is, it improves power consumption. ATA/ATAPI-4 - extension of ATA3, has Ultra DMA, ATAPI interface. E-IDE supports PIO mode3, with multiword DMA mode 1 and works with LBA and CHS. Ultra DMA requires an 80-conductor cable with 40-pin shielded connectors. The IDE Mastering standard allows an external device to control the system bus for data transfer without controlling the processor bus, but using such a bus eliminates DMA channel allocation problems and capacity limitations. In particular, it works with 8- or 16-bit data. Next came the operating modes ATA-3 (another name for EIDE), ATA-4 (frequency 16.7, 25, 33.3, another name for Ultra ATA /33), ATA-5 (frequency 66 MHz, another name Ultra ATA /66), ATA-6 (frequency 100 MHz, another name Ultra DMA 100 or UDMA 5 (100)), ATA-7 (frequency 133 MHz, another name Ultra DMA 133 or UDMA 6 (133)), ATA-8 (in development).
Tire VESA(Video Electronics Standard's Association - Association of Video Electronic Standards or VL-BUS or VLB or VESA local bus) was outdated, first appeared after the ISA bus and had four times the speed of ISA, but it had some limitations, in particular, it was possible have only 2-3 connectors, which undoubtedly reduced the computer's capabilities. It is a bus for connecting a display, but can be used for other devices; it is not an extension of the ISA bus (like previous buses). This card is directly connected to the CPU bus, bypassing the system bus. Works with system bus frequencies up to 66 MHz, used mainly with 486, sometimes with 386 computers for video cards and hard drives. A new version 2.0 was released for the Pentium, but it was not widely used and is currently practically not used.
PCI bus(Peripheral Component Interconnect - connection of peripheral components) is also not based on the ISA bus and is a completely independent, synchronous bus, developed by Intel, the first versions operated at a frequency of 33 MHz, had a 32-bit (or 64-bit) channel and is independent of central processor, that is, it allows you to transfer data while the processor is busy with other calculations. The theoretical bus throughput was 133 MB/sec, but in reality it was 80 MB/sec. This tire is still widely used today.
The PCI bus began development at the same time as the ISA bus, but was completed later. The PCI bus has more data lanes than ISA and is faster than ISA, with a total of 124 pins per connector. The bus can detect errors during data transfer and operates without a cable plug. In addition, during installation it allows you to configure the connected device, that is, the computer reads information from the device’s memory, where its main parameters are stored. The bus can work not only with a specific set of chips on the motherboard, but also with different devices, as well as in other types of computers. In addition, the PCI bus is capable of sharing interrupts and DMA channels between different devices, which was the impetus for its active implementation, while the ISA bus could not provide this.
You can connect cards to the PCI bus connector: those with power supply: 5 V (key 50, 51 pins), 3.3 V (key 12, 13) and universal (key 12, 13, 50, 51 pins). A 32-bit slot has 62 contacts on each side, a 64-bit slot has 94. This bus allows you to connect up to four devices simultaneously, that is, it can have up to four connectors. To use a larger number of connected devices, a special chip is used - a bus bridge - to connect two buses. For industrial devices there is a Compact PCI standard with 8 slots.
While the PCI bus was being developed, other industries were also developing. The clock frequency of the internal bus has increased to 100, 150 and higher MHz, the number of data lines has increased to 64 and continues to increase, however, the type of PCI bus remains 32-bit, but in the future the PCI bus will also develop.
Each slot has 256 eight-bit registers that contain configuration parameters. After turning on the computer's power, a request is made to configure the bus during the execution of the Post program; after setting the parameters, the bus can perform I/O operations. The main advantage of the bus is that data transfer occurs without the involvement of the central processor, that is, while data is being transferred from one device to another, the central processor can carry out its tasks.
The PCI 1.0 bus is 32-bit with a bandwidth of 132 MB/s, addressing up to 4 gigabytes, and PCI 2.0 is 64-bit with a bandwidth of 528 MB/s. This bus is adapted for Plug&Play technology, that is, the boards are configured by software. For industrial applications, the Compact PCI standard is used, in which up to eight devices can be installed simultaneously.
Interrupt conflict resolution on the PCI bus is achieved by allowing the bus to handle processing for each device in turn. The PCI bus provides 32 data lines at a clock frequency of 33 MHz, then became 64-bit, with a clock frequency of 66 MHz, and the new version of the bus can accommodate old PCI cards, as well as a new card in the old slot. Newer versions of PCI can increase the clock speed and allow you to use old expansion cards to run them, as well as install new cards in old slots.
AGP bus(Accelerated Graphics Port) was developed by Intel in 1997 specifically for working with a video card, at a frequency of 66 MHz it has a 32-bit data bus. Currently supplanted by the PCI-E bus. The bus allows you to use pipelining of requests, that is, sending data in the form of continuous packets. In the PCI bus, the previous data and the address for the next data are sent, after which time delays occur, and in the AGP bus, several addresses and several data are sent one after the other, which reduces the delay. It is possible to queue up to 256 requests and maintain two queues for high and low priority read/write operations. Dual transmission, that is, the transmission of two data in one clock cycle instead of one, allows you to have a throughput at a frequency of 66 MHz up to 528 MB/sec. Allows operation at frequencies up to 100 MHz and higher with higher throughput. Quad transfer allows you to transfer up to 1,056 MB/sec.
There are several standards for the AGP bus: AGP 1X, 2X, 4X, Pro and 8X. Most cards work with the 4X and 8X standard. RAM stores not only parts of the image, but also graphic textures. To ensure that the video system can only access those areas of memory that concern it, a special GART table (Graphics Address Remapping Table) is used to define these memory areas.
The bus has the ability for the video processor to directly access areas of RAM, as well as video memory, and process textures there in DiMe (Direct Memory Execution) mode, while the addressing is the same. The bus is used for Pentium Pro, Pentium II, Pentium III and Pentium IV processors, but can also work with Pentium processors.
SATA(Serial ATA) is a development of the IDE interface. Its feature is not parallel data transmission, but serial one, which, although slower, allows the use of higher frequencies without the need for signal synchronization. The first SATA 1.x standard could operate at a frequency of 1.5 GHz with a throughput of 1.2 Gbit/s (losses due to the transfer of a large amount of service information). The 2.x standard operates at a frequency of 3 GHz with a throughput of up to 2.4 Gbit/s and the 3.0 standard at a frequency of 6.0 Gbit/s, with a throughput of 4.8 Gbit/s.
To connect devices inside the system unit, they are connected to the 7-pin SATA information connector on the motherboard and a 15-pin power cable to the power supply. There are devices that allow you to connect both a 15-pin cable and a 4-pin Molex electrical power cable. Please be aware that connecting two cables at the same time may burn out the device.
There are adapters from SATA to IDE and vice versa.
eSATA(External SATA - external SATA) is designed for connecting devices in hot-swappable mode, that is, when the computer is turned on. In order to be able to do this in Windows XP, you need to install the AHCI driver. Was created in 2004. Has a connector similar to SATA, but has added connector shielding. Therefore, it is not compatible with the SATA connector, since they are electrically compatible, but not physically. The cable length has been increased to 2 meters (1 meter for SATA).
There is a combined eSATA + USB connector = Power eSATA, which has not only information lines, but also power lines.
PCI - E(or PCI Express or PCI-E) appeared in 2002, uses a star-type connection between devices, allowing hot-swapping of devices. There are several options x1, x2, x4, x8, x12, x16, x32, which have different connectors. The lower the number, the fewer pins and shorter the connector length. Devices that are designed for x8 connectors can be connected to connectors with a larger number, in this case, x12, x16, x32. This rule applies to other species.
There are three standards. Standard 1.0 allows you to transfer in one direction for x1 - 2 Gbit/s, in two directions - 4 Gbit for x1. The throughput of other types can be calculated by multiplying the above figure by the number in the name. For example, for x16 the throughput in one direction is 2 x 16 = 32 Gbit/s. Standard 2.0 was released in 2007, has a throughput in one direction (double in two directions) for x1 - 4 Gbit/s. You can also calculate throughput for other species. Standard 3.0 released in 2010, it allows you to transfer data at a speed of 8 Gbit/s. Standard 4.0 is scheduled to be released by 2015 and will be twice as fast as 3.0.
Currently, the most common on motherboards are x16 for connecting video cards and x2 for connecting other devices.
USB bus(Universal Serial Bus - universal serial bus) is designed for connecting peripheral devices (for example, keyboard, mouse, joystick, printer and others). Its mission is to connect various devices to a running computer, for example, toasters, keyboards, microwave ovens, LED lights, fans, etc., without the need to install switches, jumpers, use software (drivers), etc. for this.
First standard 1.0 appeared in 1994 and has a mode with low throughput of 1.5 Mbit/s (Low speed), with high throughput (Full-speed) up to 12 Mbit/s. The USB bus can operate in two modes: low-speed, in which the keyboard, mouse, etc. operates, with a low transmission speed (cable length - 5 meters) and high-speed mode (cable length - 3 meters), which allows you to work with maximum printer speed.
In version 1.1, existing errors were corrected.
Standard 2.0 a new mode has appeared (Hi-speed) with a throughput of 25480 Mbit/s.
You can connect devices on this bus, and the computer itself will determine the device that is connected. In this case, it is possible not only to connect a new device directly to the computer, but also to a device that is already connected to the computer. For example, you can connect a hard drive, microphone and other devices to the keyboard.
It can use a hub to which you can connect up to 127 devices and supports Plug&Play technology. In this case, the bus automatically assigns a number to the devices with which it operates. In addition to sending data, these wires also transmit electricity, but in a small amount, which is enough for the keyboard, but may not be enough for the speakers. Therefore, speakers with high output power require a separate power supply.
The bus allows you to connect devices when the computer is turned on. When connected, they request a host device, which assigns them addresses, after which they can begin to work. In addition to data, electricity is also transmitted, which is used to power devices. If there is not enough electricity, the devices can be connected to an additional power source.
In addition to increasing computer performance, the need for upgrading may arise when adding new devices, which requires the appropriate power supply power, a certain number and type of connectors for expansion cards on the motherboard and the number of free compartments inside the system unit. Over time, with the spread of the USB standard, many devices that can now be connected are not located inside, but rather brought outside the system unit. Thus, more and more external devices will be produced and the number of connectors inside the case and compartments will not be a problem when installing a large number of additional devices.
Latest standard USB 3.0 appeared in 2008, connectors are compatible with earlier standards. However, four more communication lines were added in the form of two twisted pairs and the cable itself became thicker. The connectors on the motherboard for connecting such cables are blue, and the plugs themselves have blue inserts. Thus, the maximum data transfer rate was increased to 4.8 Gbit per second, and the transfer speed increased to 600 MB per second (a figure higher than the standard USB 2.0 ten times). At the same time, the transmitted current has increased from 500 mA to 900 mA, which allows you to connect more energy-intensive devices.
Tire PCMCIA used in laptops and has the ability to transfer data over 16 bits with addressing up to 64 Megabytes, with a bus frequency of 33 megahertz. This bus allows you to connect different devices - hard drives, modems, memory expanders, etc. Many adapters are produced using PnP technology and have the ability to connect devices without turning off the computer. All devices connected to this connector have reduced power consumption. The bus has great prospects in the future and will be installed in desktop computers.
PCMCIA cards, also called PC cards, are designed for RAM, modems, hard drives, and other devices and come in three types. They have a length and width of 85x54 mm, and the thickness depends on the type. Type I has a thickness of 3.3 mm, type II - 5 mm, type III - 10.5 mm. The card is inserted into a slot on the ISA bus designed for these cards, also called PCMCIA.
Type I is used for RAM, sometimes for modems or a network card, has a 16-bit interface, thickness 3.3 mm, type II is for the same devices, but they are thicker (5 mm), type III can also install a hard drive (thickness 10. 5 mm). The laptop has a compartment where you can install either one type I or II card, or in modern models - two cards of type I and II or one type III.
For the modem, at the end of the card there is a special connector (X-jack) to which the wire is connected; at the other end there is a telephone connector (RG11) for connecting to a telephone line. When installing, you just need to insert the card into the hole until it clicks, and in order to remove it, you need to press the adjacent key, and the card will pop out. PC Card AT is a PCMCIA connector for connecting to notebook and desktop computers.
Card Bus is a further development of PC Cards, which transmit data via a 32-bit interface (PCMCIA cards became known as PC Cards). The bus connects the card to the video system, allowing it to bypass the ISA bus. This bus is called Zoomed Video Port - enlarged video port.
IEEE 1394– developed by the Institute of Electrical and Electronics Engineers (IEEE) based on the Apple bus – FireWire in 1995, where the number 1394 indicates the serial number of the tire that was developed by this organization. The bus allows you to connect up to 16 devices to one node, and each device is assigned a number, which is 16 bits in size, that is, more than 64,000 devices can be addressed in total. Up to 63 devices are connected to each bus, and each node is assigned a number consisting of 6 bits. 1023 buses can be connected to each other using bridges, each of which has a capacity of 10 bits; the bus can be “hot-swappable”. Each new device can be connected to any free port; on one device there are from one to three of them, but up to 27 are possible. The only exception is the prohibition of organizing device loops, since the bus supports a tree structure.
There are three classes of devices with 98.3 data transmission; 196.6 and 339.2 Mbps, or they are usually rounded up to 100, 200 and 400 Mbps according to the IEEE 1394a standard and 800 and 1600 according to the IEEE 1394b standard. According to the IEEE 1394.1 standard, developed in 2004, you can connect up to 64,449 devices; according to the IEEE 1394c standard, developed in 2006, you can use an Ethernet cable. In this case, the maximum cable length is up to 100 meters, and the speed is up to 800 Mbit/s.
There are three types of connectors: 4 pin – without power, installed on laptops and video cameras (IEEE 1394a without power), 6 pin – with additional two contacts for power(IEEE 1394a) and 9 pin with additional contacts for receiving and transmitting(IEEE 1394 b). There may also be an RJ-45 connector(IEEE 1394c) .
If the cable consists of 6 copper wires, two for power, the remaining two pairs for data, each pair is shielded and all wires together are also shielded. Since a power supply of 8 to 40 volts is provided at a current of up to 1.5 amperes, many devices do not require additional connection to the network. Cables up to 4.5 meters can be installed between two devices, and the bus connectors are simple and easy to connect.
The bus operates in synchronous and asynchronous modes. Asynchronous transmission sends data organized in packets and repeats the transmission if errors occur, which is important for accurate data transfer. Synchronous transmission is used in multimedia to transmit audio and video data, but if the data is lost, this is not critical, since the next portion of data is transmitted.
The IEEE 1394 bus transmits data digitally, so the video image quality is better than analog. The computer can programmatically turn on and off devices connected to it. The bus is independent of the computer, that is, it can operate in the absence of a computer, for example, to transfer data from a video camera to a VCR. This bus is supported by Windows 98 (update required), Windows ME, Windows 2000, Windows XP and others.
To speed up the work, it was introduced host bus(sometimes called the processor bus). Designed to transfer 64-bit data between the processor, RAM and L2 cache and operates at 50, 60, 66, 75, 100, 133 MHz, while the PCI bus operates at half the frequency (25 ; 30; 33; 37.5 MHz).
Exploitation. If one of the old cards stops working, you can try to remove it and clean the contacts with an ordinary eraser, which will remove deposits and oxide. After installation, check the operation of the board. It is advisable to cover unused slots with special covers.