PCI bus versions. PCI Express - what is it and main features What are pci e lanes

Currently, in the field of complex electronics, there is an active and rapid introduction of new technologies, as a result of which some components of the system may become obsolete and cannot be updated, etc.

In this regard, it is necessary to connect various add-ons to them and, for which certain adapters are often required.

In this article, we will consider the adapter pci-e pci how it works and what features it has.

Definition

What is this device and what is it for? Strictly speaking, this is an input and output bus that connects to a personal computer.

To this bus itself, that is, to the adapter, you can connect a certain (different depending on the configuration) number of external peripherals.

By using serial connection these peripherals are connected to the computer.

The main characteristic of such a device is its throughput.

It is she who characterizes (in the general case) the quality of work, its speed and the speed of the computer and the elements connected in this way.

The throughput characteristic is expressed in the number of connection lines (from 1 to 32).

Depending on this basic characteristic, the price can also vary significantly. this device. That is, the better this characteristic is (the indicator is higher), the higher the cost of such a device. In addition, much depends on the status of the manufacturer, the reliability of the equipment and its durability. On average, the price starts from 250-500 rubles (for Asian products with low bandwidth), up to 2000 rubles (for European and Japanese devices with high bandwidth).

Specifications

From a technical point of view, such a device has three components:

Above it was written about the exceptional importance of the bandwidth of the device for its normal functioning.

What is throughput? To answer this question, you need to understand the principle of operation of such an adapter.

It is capable of simultaneous bi-directional (card-to-peripheral and peripheral-to-card) equipment connection.

In this case, data transmission can occur both over one or several lines.

The more such lines, the more stable the device works, the higher its bandwidth and the faster the peripheral equipment will be.

Important! Depending on the number of lines, the device can have different configurations: x1, x2, x4, x8, x12, x16, x32. The figure indicates directly the number of lanes for two-way simultaneous transmission of information. Each of these strips consists of two pairs of wires (for transmission in two directions).

As can be seen from the description, this configuration significantly affects the cost of the device.

But what practical significance does it have, does it really make sense to spend extra when buying a device?

It directly depends on how much you plan to connect to motherboard- the more there are, the more bandwidth the device needs to maintain stable computer operation.

Encryption

With such a system of information transmission, a specific system is used to protect it from distortion and loss.

This protection method is designated 8V/10V.

The point is that in order to transmit the 8 bits of necessary information, an additional 2 service bits must be used to implement security and protection against distortion.

When such an adapter is used, 20% is constantly transferred to the computer. service information, which does not carry any load and is not needed by the user. But it is she who, although it loads (however, very slightly), ensures the stability of the bus and peripheral devices.

Story

In the early 2000s, the AGP expansion slot was actively used, it was with its help that .

But, at some point, its maximum technically possible performance was achieved and it became necessary to create a new type of adapter.

And soon PCI-E appeared - it was 2002.

Immediately there was a need for an adapter that would allow you to install new graphics solutions in an outdated expansion slot or vice versa.

Therefore, in 2002, many developers and manufacturers began to seriously create such an adapter.

At that time, the device had one important quality - the ability to upgrade a PC by spending minimal amounts on it, because instead of replacing the motherboard, a relatively inexpensive adapter was enough.

But the development was not successful, because at that time they cost almost the same as the first adapters, and therefore it became necessary to develop a simpler adapter configuration.

Interestingly, manufacturers have also consistently increased the throughput of such devices. If for the first configurations it was no more than 8 Gb / s, then for the second it was already 16 Gb / s, and for the third - 64 Gb / s. This met the requirements of increasing loads arising from the modernization of peripheral devices.

At the same time, slots with different speed transfers are compatible with any devices of a lower "high-speed" level.

That is, if you connect a second or first generation graphics platform to the third generation slot, the slot will automatically switch to a different speed mode corresponding to the connected device.

Differences between PCI and PCI-E

What are the specific differences between these two configurations?

In terms of its technical and operational characteristics, PCI is similar to AGP, while PCI-E is a fundamentally new development.

Whereas PCI provides parallel transfer of information, PCI-E provides serial, due to which much more high speed information transfer and performance even with the use of an adapter.

Why is it needed?

Why is such an adapter needed and what can it be used for, is it possible to do without it?

It must be understood that most users do without this equipment because it is not necessary even on old computers subject to significant wear and tear.

This is additional equipment, which in some cases will improve the functionality of your PC, but without which an ordinary user can do without.

In fact, the use of such an adapter gives only one main advantage - the ability to connect a certain number of peripheral devices to the memory card, while it is impossible to connect so many of them directly. For example, in this way you can connect a discrete video or in addition to the main one.

Also, a fairly convenient feature can be the simultaneous quick shutdown of all peripheral devices if necessary.

For example, in the case when the computer performance decreases or for other reasons. In this case, the user does not need to programmatically disable components for a long time.

Disadvantages and possible problems

There are a number of significant disadvantages of these devices, and problems that they can cause during operation.

Most often, there are the following difficulties:

• The device is quite large, because it does not always fit in miniature ones;
• The second point automatically follows from the first point - the adapter is not designed to work with laptops;
• Stable operation of many devices is only possible in combination with low-profile cards;
• There is always a possibility of failure, software or technical (minor) incompatibility of the device with motherboard your PC (everything is complicated by the fact that most of these devices are declared universal, although they actually work with many less stable than with others);
• Some volumes are constantly occupied random access memory PC due to .

If there is a need to connect additional devices to the motherboard, then it makes sense to try this method. But you need to remember that normal stable operation is possible only with a high-quality and productive motherboard and peripheral device.

Interface support PCI Express 3.0 in motherboards - a real advantage or a marketing ploy?

During the last months in model range different manufacturers began to appear motherboards, which declared support for the PCI Express 3.0 interface. ASRock, MSI and GIGABYTE were the first to announce such solutions. However, at the moment, there are absolutely no chipsets, graphics and central processors on the market that would support the PCI Express 3.0 interface.

Recall that the PCI Express 3.0 standard was approved last year. It has numerous advantages over its predecessors, so it is not surprising that graphics card and motherboard manufacturers want to implement it in their solutions as soon as possible. However, the currently existing chipsets from Intel and AMD are limited to supporting the PCI Express 2.0 standard. The only hope to take advantage of the PCI Express 3.0 interface in the near future lies with new Intel processors Ivy Bridge, the announcement of which is scheduled only for March-April next year. These processors have an integrated controller PCI bus Express 3.0, but only graphics chips will be able to use it, since other components use the chipset controller.

Note that the matter is not limited to just replacing the processor. Additional update needed BIOS settings and chipset firmware. In addition, on motherboards with several PCI Express x16 slots, there is a problem with "switches" - small microcircuits that are located near each slot and are responsible for the operational reconfiguration of the number of dedicated lines. These "switches" must also be compatible with the PCI Express 3.0 interface. It should be noted that nForce 200 or Lucid bridge chips support only the PCI Express 2.0 standard and they cannot work with the PCI Express 3.0 specification.

The last argument is that at the moment motherboard manufacturers do not have engineering samples of new Intel Ivy Bridge processors or new graphics chips that support the PCI Express 3.0 specification at the hardware level. Therefore, the announced compatibility with this high-speed interface is theoretical and cannot, at the moment, be practically confirmed.

Thus, support for the PCI Express 3.0 specification by modern motherboards is purely a marketing ploy, the benefits from which the user will be able to get only in a few months by replacing the processor and updating the software components.

Spring 1991 Intel completes the development of the first breadboard version of the PCI bus. The engineers were tasked with developing a low-cost and high-performance solution that would allow them to realize the capabilities of the 486, Pentium and Pentium Pro processors. In addition, it was necessary to take into account the mistakes made by VESA when designing the VLB bus (the electrical load did not allow connecting more than 3 expansion boards), as well as to implement automatic tuning devices.

In 1992, the first version of the PCI bus appears, Intel announces that the bus standard will be open, and creates the PCI Special Interest Group. Thanks to this, any interested developer gets the opportunity to create devices for the PCI bus without the need to purchase a license. The first version of the bus had a clock speed of 33 MHz, could be 32- or 64-bit, and devices could work with signals of 5 V or 3.3 V. Theoretically, the bus bandwidth was 133 MB / s, but in reality the bandwidth was about 80 MB/s

Main characteristics:

• bus frequency - 33.33 or 66.66 MHz, synchronous transmission;
• bus width - 32 or 64 bits, multiplexed bus (address and data are transmitted over the same lines);
• peak throughput for the 32-bit version running at 33.33 MHz is 133 MB/s;
• memory address space - 32 bits (4 bytes);
• address space of input-output ports - 32 bits (4 bytes);
• configuration address space (for one function) - 256 bytes;
• voltage - 3.3 or 5 V.

Photo connectors:

MiniPCI - 124 pin
MiniPCI Express MiniSata/mSATA - 52 pin
Apple MBA SSD, 2012
Apple SSD, 2012
Apple PCIe SSD
MXM, Graphics Card, 230 / 232 pin
MXM2 NGIFF 75 pins KEY A PCIe x2 KEY B PCIe x4 Sata SMBus
MXM3, Graphics Card, 314 pin
PCI 5V
PCI Universal
PCI-X 5v
AGP Universal
AGP 3.3v
AGP 3.3 v + ADS Power
PCIe x1
PCIe x16
Custom PCIe
ISA 8bit
ISA 16bit
eISA
VESA
NuBus
PDS
PDS
Apple II / GS Expansion slot
PC/XT/AT expansion bus 8bit
ISA (industry standard architecture) - 16 bit
eISA
MBA - Micro Bus architecture 16 bit
MBA - Micro Bus architecture with video 16 bit
MBA - Micro Bus architecture 32 bit
MBA - Micro Bus architecture with video 32 bit
ISA 16 + VLB (VESA)
Processor Direct Slot PDS
601 Processor Direct Slot PDS
LC Processor Direct Slot PERCH
NuBus
PCI (Peripheral Computer Interconnect) - 5v
PCI 3.3v
CNR (Communications/network Riser)
AMR (Audio / Modem Riser)
ACR (Advanced Communication Riser)
PCI-X (Peripheral PCI) 3.3v
PCI-X 5v
PCI 5v + RAID option - ARO
AGP 3.3v
AGP 1.5v
AGP Universal
AGP Pro 1.5v
AGP Pro 1.5v+ADC power
PCIe (peripheral component interconnect express) x1
PCIe x4
PCIe x8
PCIe x16

PCI 2.0

The first version of the basic standard, which was widely adopted, used both cards and slots with a signal voltage of only 5 volts. Peak bandwidth - 133 MB / s.

PCI 2.1 - 3.0

They differed from version 2.0 in the possibility of simultaneous operation of several bus masters (eng. bus-master, the so-called competitive mode), as well as the appearance of universal expansion cards capable of operating both in slots using a voltage of 5 volts and in slots using 3 .3 volts (with a frequency of 33 and 66 MHz, respectively). Peak throughput for 33 MHz is 133 MB/s and for 66 MHz is 266 MB/s.

• Version 2.1 - work with cards designed for voltage of 3.3 volts and the presence of appropriate power lines were optional.
• Version 2.2 - expansion cards made in accordance with these standards have universal key power connectors and are able to work in many later varieties of PCI bus slots, and also, in some cases, in version 2.1 slots.
• Version 2.3 - Not compatible with PCI cards designed to use 5 volts, despite continued use of 32-bit 5-volt keyed slots. Expansion cards have universal connector, but are not capable of working in 5-volt slots of earlier versions (up to and including 2.1).
• Version 3.0 - completes the transition to 3.3 volt PCI cards, 5 volt PCI cards are no longer supported.

PCI 64

An extension to the core PCI standard introduced in version 2.1 that doubles the number of data lanes, and thus the bandwidth. The PCI 64 slot is an extended version of the regular PCI slot. Formally, the compatibility of 32-bit cards with 64-bit slots (provided there is a common supported signal voltage) is complete, while the compatibility of a 64-bit card with 32-bit slots is limited (in any case, there will be a performance loss). Operates at a clock frequency of 33 MHz. Peak bandwidth - 266 MB / s.

• Version 1 - uses a 64-bit PCI slot and a voltage of 5 volts.
• Version 2 - uses a 64-bit PCI slot and a voltage of 3.3 volts.

PCI 66

PCI 66 is a 66 MHz evolution of PCI 64; uses a voltage of 3.3 volts in the slot; cards have a universal or 3.3 V form factor. Peak throughput is 533 MB/s.

PCI 64/66

The combination of PCI 64 and PCI 66 allows four times the data transfer rate compared to the base PCI standard; uses 64-bit 3.3-volt slots compatible only with universal ones, and 3.3-volt 32-bit expansion cards. PCI64/66 cards have either universal (but limited compatibility with 32-bit slots) or 3.3-volt form factor (the latter option is fundamentally incompatible with 32-bit 33 MHz slots of popular standards). Peak bandwidth - 533 MB / s.

PCI-X

PCI-X 1.0 is an expansion of the PCI64 bus with the addition of two new operating frequencies, 100 and 133 MHz, as well as a separate transaction mechanism to improve performance when multiple devices are working simultaneously. Generally backwards compatible with all 3.3V and universal PCI cards. PCI-X cards are usually made in 64-bit 3.3 format and have limited backward compatibility with PCI64/66 slots, and some PCI-X cards are in universal format and are able to work (although this has almost no practical value) in the usual PCI 2.2/2.3. In complex cases, in order to be completely confident in the performance of the combination of the motherboard and expansion card, you need to look at the compatibility lists (compatibility lists) of the manufacturers of both devices.

PCI-X 2.0

PCI-X 2.0 - further expansion of PCI-X 1.0 capabilities; frequencies 266 and 533 MHz have been added, as well as parity error correction during data transmission (ECC). Allows splitting into 4 independent 16-bit buses, which is used exclusively in embedded and industrial systems ; the signal voltage is reduced to 1.5 V, but the connectors are backward compatible with all cards using a 3.3 V signal voltage. Currently, for the non-professional segment of the market for high-performance computers (powerful entry level) that use the PCI-X bus, there are very few motherboards that support the bus. An example of a motherboard for this segment is the ASUS P5K WS. In the professional segment, it is used in RAID controllers, in SSD drives for PCI-E.

Mini PCI

Form factor PCI 2.2, intended for use mainly in laptops.

PCI Express

PCI Express, or PCIe, or PCI-E (also known as 3GIO for 3rd Generation I/O; not to be confused with PCI-X and PXI) - computer bus(although it is not a bus at the physical layer, being a point-to-point connection) using programming model PCI bus and high performance physical protocol based on serial communication. The development of the PCI Express standard was started by Intel after the abandonment of the InfiniBand bus. Officially, the first basic PCI Express specification appeared in July 2002. The PCI Special Interest Group is involved in the development of the PCI Express standard.

Unlike the PCI standard, which used a common bus for data transfer with several devices connected in parallel, PCI Express, in general, is a packet network with star topology. PCI Express devices communicate with each other through a medium formed by switches, with each device directly connected by a point-to-point connection to the switch. In addition, the PCI Express bus supports:

• hot swapping of cards;
• guaranteed bandwidth (QoS);
• energy management;
• integrity control of transmitted data.

The PCI Express bus is intended to be used as a local bus only. Since the PCI Express programming model is largely inherited from PCI, existing systems and controllers can be modified to use the PCI Express bus by replacing only physical layer, without modification software. The high peak performance of the PCI Express bus allows it to be used instead of AGP buses, and even more so PCI and PCI-X. The de facto PCI Express has replaced these buses in personal computers.

• MiniCard (Mini PCIe) is a replacement for the Mini PCI form factor. Buses are displayed on the Mini Card connector: x1 PCIe, 2.0 and SMBus.
  • M.2 is the second version of Mini PCIe, up to x4 PCIe and SATA.
• ExpressCard - Similar to the PCMCIA form factor. The x1 PCIe and USB 2.0 buses are output to the ExpressCard connector, ExpressCard cards support hot plugging.
• AdvancedTCA, MicroTCA - form factor for modular telecommunications equipment.
  
• Mobile PCI Express Module (MXM) is an industrial form factor created for laptops by NVIDIA. It is used to connect graphics accelerators.
• Cable specifications PCI Express allow you to bring the length of one connection to tens of meters, which makes it possible to create a computer, the peripherals of which are located at a considerable distance.
  
• StackPC - specification for building stackable computer systems. This specification describes the StackPC , FPE expansion connectors and their relative position.

Despite the fact that the standard allows x32 lines per port, such solutions are physically cumbersome and are not available.

PCI Express 2.0

The PCI-SIG released the PCI Express 2.0 specification on January 15, 2007. Main innovations in PCI Express 2.0:

• Increased throughput: 500 MB/s single line bandwidth, or 5 GT/s ( Gigatransactions/s).
• Improvements have been made to the transfer protocol between devices and the software model.
• Dynamic control speed (to control the speed of communication).
• Bandwidth Alert (to notify software of changes in bus speed and width).
• Access Control Services - Optional point-to-point transaction management capabilities.
• Execution timeout control.
• Reset at the function level - an optional mechanism for resetting functions (eng. PCI functions) inside the device (eng. PCI device).
• Power limit override (to override the slot power limit when connecting devices that consume more power).

PCI Express 2.0 is fully compatible with PCI Express 1.1 (old ones will work in motherboards with new connectors, but only at 2.5GT/s, since older chipsets cannot support double data transfer rates; newer video adapters will work without problems in old PCI Express 1.x standard slots).

PCI Express 2.1

In terms of physical characteristics (speed, connector) it corresponds to 2.0, the software part has added functions that are planned to be fully implemented in version 3.0. Since most motherboards are sold with version 2.0, having only a video card with 2.1 does not allow 2.1 mode to be enabled.

PCI Express 3.0

In November 2010, the PCI Express 3.0 version specifications were approved. The interface has a data transfer rate of 8 GT/s ( Gigatransactions/s). But despite this, its real throughput was still doubled compared to the PCI Express 2.0 standard. This was achieved thanks to the more aggressive 128b/130b encoding scheme, where 128 bits of data sent over the bus are encoded in 130 bits. At the same time, full compatibility with previous versions PCI Express. PCI Express 1.x and 2.x cards will work in slot 3.0 and vice versa, PCI Express 3.0 card will work in slots 1.x and 2.x.

PCI Express 4.0

The PCI Special Interest Group (PCI SIG) has stated that PCI Express 4.0 may be standardized before the end of 2016, but as of mid-2016, when a number of chips were already in production, media reported that standardization is expected in early 2017. It is expected that he will have a bandwidth of 16 GT / s, that is, it will be twice as fast as PCIe 3.0.

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Attention! This article is about the PCI bus and its PCI64 and PCI-X derivatives! Do not confuse it with the newer tire ("PCI Express"), which is completely incompatible with the tires described in this FAQ.

PCI 2.1- differed from 2.0 by the possibility of simultaneous operation of several bus-master devices (the so-called competitive mode), as well as the appearance of universal expansion cards capable of operating in both 5V and 3.3V slots. The ability to work with 3.3V cards and the presence of appropriate power lines in version 2.1 was optional. PCI66 and PCI64 extensions appeared.

PCI 2.2- a version of the basic bus standard that allows connection of expansion cards with a signal voltage of both 5V and 3.3V. The 32-bit versions of these standards were the most common slot type at the time the FAQ was written. 32-bit, 5V type slots are used.
Expansion cards made in accordance with these standards have a universal connector and are able to work in almost all later varieties of PCI bus slots, and also, in some cases, in 2.1 slots.

PCI 2.3- the next version of the common standard for the PCI bus, expansion slots that comply with this standard are not compatible with PCI 5V cards, despite the continued use of 32-bit slots with a 5V key. Expansion cards have a universal connector, but are not able to work in 5V slots of earlier versions (up to 2.1 inclusive).
We remind you that the supply voltage (not signal!) 5V is stored absolutely on all versions of the PCI bus connectors.

PCI 64- an extension of the basic PCI standard, introduced in version 2.1, doubling the number of data lines, and, consequently, the throughput. The PCI64 slot is an extended version of the regular PCI slot. Formally, the compatibility of 32-bit cards with 64-bit slots (subject to the presence of a common supported signal voltage) is complete, and the compatibility of a 64-bit card with 32-bit slots is limited (in any case, there will be a loss of performance), exact data in each specific case can be found in the specifications of the device.
The first versions of PCI64 (derived from PCI 2.1) used a 64-bit 5V PCI slot and ran at 33MHz.

PCI 66- an extension of the PCI standard that appeared in version 2.1 with support for a clock frequency of 66 MHz, as well as PCI64, allows you to double the bandwidth. Starting with version 2.2, it uses 3.3V slots (the 32-bit version is almost never found on a PC), cards have a universal or 3.3V form factor. (There were also solutions based on version 2.1, casuistically rare on the PC 5V 66MHz market, such slots and boards were only compatible with each other)

PCI 64/66- A combination of the above two technologies, it can quadruple the data transfer rate compared to the basic PCI standard, and uses 64-bit 3.3V slots, compatible only with universal and 3.3V 32-bit expansion cards. PCI64/66 cards have a universal (with limited compatibility with 32-bit slots) or 3.3V form factor (the latter option is fundamentally not compatible with 32-bit 33MHz slots of popular standards)
Currently, the term PCI64 means exactly PCI64/66, since 33MHz 5V 64-bit slots have not been used for a long time.

PCI-X 1.0- Expansion of PCI64 with the addition of two new operating frequencies, 100 and 133 MHz, as well as a separate transaction mechanism to improve performance when running multiple devices at the same time. Generally backwards compatible with all 3.3V and universal PCI cards.
PCI-X cards are usually made in 64-bit 3.3 format and have limited backward compatibility with PCI64/66 slots, and some PCI-X cards are in a universal format and can work (although this has almost no practical value) in regular PCI 2.2 /2.3.
In difficult cases, in order to be completely confident in the performance of the combination of motherboard and expansion card you have chosen, in the case you need to look at the compatibility lists of the manufacturers of both devices.

PCI-X 2.0- further expansion of the capabilities of PCI-X 1.0, added speeds of 266 and 533 MHz, as well as parity error correction during data transfer. (ECC). It allows splitting into 4 independent 16-bit buses, which is used exclusively in embedded and industrial systems, the signal voltage is reduced to 1.5V, but the connectors are backward compatible with all cards using a 3.3V signal voltage.

PCI-X 1066/PCI-X 2133- projected future versions of the PCI-X bus, with resulting operating frequencies of 1066 and 2133 MHz, respectively, originally intended for connecting 10 and 40 Gbit Ethernet adapters.

For all variants of the PCI-X bus, there are the following restrictions on the number of devices connected to each bus:
66MHz - 4
100MHz - 2
133MHz - 1 (2, if one or both devices are not on expansion boards, but are already integrated on one board along with the controller)
266.533MHz and above -1.

That is why, in some situations, to ensure the stability of several installed devices it is necessary to limit the maximum frequency of the used PCI-X bus (usually this is done by jumpers)

CompactPCI- a standard for connectors and expansion cards used in industrial and embedded computers. Mechanically not compatible with any of the "common" standards.

MiniPCI- a standard for boards and connectors for integration into laptops (usually used for adapters wireless network) and directly to the surface. It is also mechanically incompatible with anything other than itself.

Types of PCI expansion cards:

Summary table of constructs of cards and slots depending on the version of the standard:

Summary table of compatibility of cards and slots depending on the version and design:

In this article, we will explain the reasons for the success of the PCI bus and describe the high-performance technology that is coming to replace it - the PCI Express bus. We will also look at the history of development, the hardware and software levels of the PCI Express bus, the features of its implementation and list its advantages.

When in the early 1990s she appeared, then on her own technical specifications significantly outperformed all buses that existed up to that point, such as ISA, EISA, MCA and VL-bus. At that time, the PCI bus (Peripheral Component Interconnect - interaction of peripheral components), operating at a frequency of 33 MHz, was well suited for most peripheral devices. But today the situation has changed in many ways. First of all, the clock speeds of the processor and memory have increased significantly. For example, the clock frequency of processors has increased from 33 MHz to several GHz, while the operating frequency of PCI has increased to only 66 MHz. The advent of technologies such as gigabit ethernet and IEEE 1394B threatened that the entire bandwidth of the PCI bus could go to serve a single device based on these technologies.

At the same time, the PCI architecture has a number of advantages over its predecessors, so it was not rational to completely revise it. First of all, it does not depend on the type of processor, it supports buffer isolation, bus mastering technology (bus capture) and PnP technology in full. Buffer isolation means that the PCI bus operates independently of the internal processor bus, which allows the processor bus to function independently of the speed and load of the system bus. Thanks to the bus capture technology, peripheral devices have the ability to directly control the process of data transfer on the bus, instead of waiting for help from CPU which would affect system performance. Finally, Plug and Play support allows automatic configuration and configuration of devices using it and avoids fuss with jumpers and switches, which pretty much ruined the lives of owners of ISA devices.

Despite the undoubted success of PCI, at the present time it faces serious problems. Among them are limited bandwidth, lack of real-time data transmission functions and lack of support for next-generation network technologies.

Comparative characteristics of various PCI standards

It should be noted that the actual throughput may be less than the theoretical one due to the principle of the protocol and the features of the bus topology. In addition, the total bandwidth is distributed among all devices connected to it, therefore, the more devices sit on the bus, the less bandwidth goes to each of them.

Such standard improvements as PCI-X and AGP were designed to eliminate its main drawback - low clock speed. However, increasing the clock frequency in these implementations has resulted in a reduction in the effective length of the bus and the number of connectors.

The new generation of the bus, PCI Express (or PCI-E for short), was first introduced in 2004 and was designed to solve all the problems that its predecessor faced. Today, most new computers are equipped with a PCI Express bus. Although they also have standard PCI slots, the time is not far off when the bus will become history.

PCI Express Architecture

The bus architecture has a layered structure as shown in the figure.

The bus supports the PCI addressing model, which allows all currently existing drivers and applications to work with it. In addition, the PCI Express bus uses standard mechanism PnP provided by the previous standard.

Consider the purpose of the various levels of organization PCI-E. On the program level bus read / write requests are formed, which are transmitted at the transport level using a special packet protocol. The data layer is responsible for error-correcting coding and ensures data integrity. The basic hardware layer consists of a double simplex channel consisting of a transmit and receive pair, collectively referred to as a line. The total bus speed of 2.5 Gb/s means that the throughput for each PCI Express lane is 250 Mb/s each way. If we take into account the overhead costs of the protocol, then about 200 Mb / s is available for each device. This throughput is 2-4 times higher than what was available for PCI devices. And, unlike PCI, if the bandwidth is distributed among all devices, then it goes to each device in full.

To date, there are several versions of the PCI Express standard, which differ in their bandwidth.

PCI Express x16 bus bandwidth for different versions PCI-E, Gb/s:

• 32/64
• 64/128
• 128/256

PCI-E bus formats

At the moment, various options for PCI Express formats are available, depending on the purpose of the platform - a desktop computer, laptop or server. Servers that require more bandwidth have more PCI-E slots, and those slots have more trunks. In contrast, laptops may only have one line for medium-speed devices.

Video card with PCI Express x16 interface.

PCI Express expansion cards are very similar to PCI cards, but the PCI-E connectors are more grippy to ensure the card won't slip out of the slot due to vibration or during shipping. There are several form factors of PCI Express slots, the size of which depends on the number of lanes used. For example, a bus with 16 lanes is referred to as PCI Express x16. Although the total number of lanes can be as high as 32, in practice, most motherboards nowadays are equipped with a PCI Express x16 bus.

Smaller form factor cards can be plugged into larger form factor slots without compromising performance. For example, a PCI Express x1 card can be plugged into a PCI Express x16 slot. As in the case of the PCI bus, you can use a PCI Express extender to connect devices if necessary.

The appearance of the connectors various types on the motherboard. From top to bottom: PCI-X slot, PCI Express x8 slot, PCI slot, PCI Express x16 slot.

Express Card

The Express Card standard offers a very simple way to add hardware to a system. The target market for Express Card modules are laptops and small PCs. Unlike traditional expansion boards desktop computers, the Express card can connect to the system at any time while the computer is running.

One of the popular varieties of Express Card is the PCI Express Mini Card, designed as a replacement for Mini PCI form factor cards. A card created in this format supports both PCI Express and USB 2.0. PCI Express Mini Card dimensions are 30×56 mm. PCI Express Mini Card can connect to PCI Express x1.

Benefits of PCI-E

PCI Express technology has gained advantages over PCI in the following five areas:

1. Better performance. With just one lane, the throughput of PCI Express is twice that of PCI. In this case, the throughput increases in proportion to the number of lines in the bus, the maximum number of which can reach 32. An additional advantage is that information can be transmitted along the bus in both directions simultaneously.
2. Simplification of input-output. PCI Express takes advantage of buses such as AGP and PCI-X while offering a less complex architecture and relatively simple implementation.
3. Layered architecture. PCI Express offers an architecture that can adapt to new technologies without the need for significant software upgrades.
4. New generation I/O technologies. PCI Express gives you new opportunities to receive data with the help of simultaneous data transfer technology, which ensures that information is received in a timely manner.
5. Ease of use. PCI-E greatly simplifies system upgrades and expansions by the user. Additional formats Express cards such as the ExpressCard greatly increase the ability to add high-speed peripherals to servers and laptops.

Conclusion

PCI Express is a bus technology for connecting peripherals, replacing technologies such as ISA, AGP, and PCI. Its use significantly increases the performance of the computer, as well as the user's ability to expand and update the system.