Maximum pci speed. PCI-Express interface, its main characteristics and backward compatibility

Almost all modern motherboards are this moment equipped with a PCI-E x16 expansion slot. This is not surprising: a discrete graphics accelerator is installed in it, without which creating a productive personal computer is generally impossible. It is about its background of appearance, technical specifications And possible modes work will be discussed further.

Background to the appearance of the expansion slot

In the early 2000s, with the AGP expansion slot, which at that time was used for installation, a situation arose when the maximum level of performance was reached and its capabilities were no longer sufficient. As a result of this, the PCI-SIG consortium was created, which began developing the software and hardware components of the future slot for installing graphics accelerators. The fruit of his creativity was the first specification in 2002 PCI Express 16x 1.0.

Some companies, to ensure compatibility between the two ports for installing discrete graphics adapters that existed at that time, developed special devices, which allowed the installation of outdated graphic solutions into the new expansion slot. In the language of professionals, this development had its own name - PCI-E x16/AGP adapter. Its main purpose is to minimize the cost of upgrading a PC by using components from the previous configuration system unit. But this practice has not become widespread due to the fact that video cards entry level on the new interface had a cost almost equal to the price of the adapter.

In parallel with this, simpler modifications of this expansion slot were created for external controllers, which replaced the PCI ports familiar at that time. Despite their external similarity, these devices were significantly different. If AGP and PCI could boast of parallel information transfer, then PCI Express was serial interface. Its higher performance was ensured by a significantly increased data transfer rate in duplex mode(information in this case could be transmitted in two directions at once).

Transfer rate and encryption method

In the designation of the PCI-E x16 interface, the number indicates the number of lanes used for data transfer. IN in this case there are 16 of them. Each of them, in turn, consists of 2 pairs of wires for transmitting information. As noted, more high speed is ensured by the fact that these pairs operate in duplex mode. That is, the transfer of information can go in two directions at once.

To protect against possible loss or distortion of transmitted data, it is used in this interface special system information protection, which is called 8V/10V. This designation is deciphered as follows: for the correct and correct transmission of 8 bits of data, they must be supplemented with 2 service bits to perform a correctness check. In this case, the system is forced to transmit 20 percent of service information, which does not carry a useful load for the computer user. But this is the price to pay for reliable and stable work graphics subsystem of a personal computer, and you certainly can’t do without it.

PCI-E versions

The PCI-E x16 connector is externally the same on all motherboards. Only the speed of information transfer in each case may differ significantly. As a result, the performance of the device is also different. And this one has modifications GUI such:

• 1st PCI modification - Express x16 v. 1.0 had theoretical throughput at 8 Gb/s.
• 2nd generation PCI - Express x16 v. 2.0 already boasted twice the throughput of 16 Gb/s.
• A similar trend has continued for the third version of this interface. In this case, this figure was set at 64 Gb/s.

It is impossible to distinguish visually by the location of the contacts. At the same time, they are compatible with each other. For example, if you install a graphics card in a version 3.0 slot that matches physical level 2.0 specifications, then the entire processing system will automatically switch to the lowest speed mode (that is, 2.0) and will continue to function with a throughput of 64 Gb/s.

First generation PCI Express

As noted earlier, PCI Express was first introduced in 2002. Its release marked the emergence personal computers with several graphics adapters, which, moreover, could boast increased performance even with one accelerator installed. The AGP 8X standard allowed for a throughput of 2.1 Gb/s, and the first revision of PCI Express - 8 Gb/s.

Of course, there is no need to talk about an eightfold increase. 20 percent of the increase was used to transfer service information, which made it possible to find errors.

Second modification of PCI-E

The first generation of this one was replaced in 2007 by PCI-E 2.0 x16. 2nd generation video cards, as noted earlier, were physically and software compatible with the first modification of this interface. Only in this case did the performance decrease significantly graphics system up to the PCI Express 1.0 16x interface version level.

Theoretically, the information transfer limit in this case was equal to 16 Gb/s. But 20 percent of the resulting increase was spent on proprietary information. As a result, in the first case, the actual transfer was equal to: 8 Gb/s - (8 Gb/s x 20%: 100%) = 6.4 Gb/s. And for the second execution of the graphical interface, this value was already this: 16 Gb/s - (16 Gb/s x 20%: 100%) = 12.8 Gb/s. Dividing 12.8 Gb/s by 6.4 Gb/s, we get a real practical performance increase of 2 times between the 1st and 2nd versions of PCI Express.

Third generation

Latest and most current update this interface was released in 2010. The peak speed of PCI-E x16 in this case increased to 64 Gb/s, and the maximum power of the graphics adapter without additional food in this case it can be equal to 75 W.

Configuration options with multiple graphics accelerators in one PC. Their pros and cons

One of the most important innovations of this interface is the ability to have multiple x16 graphics adapters at once. In this case, video cards are combined with each other and form, essentially, a single device. Their overall performance is summed up, and this allows you to significantly increase the performance of your PC in terms of processing the output image. For solutions from NVidia this mode is called SLI, and for GPUs from AMD - CrossFire.

The future of this standard

The PCI-E x16 slot will certainly not change in the foreseeable future. This will allow more powerful video cards to be used as part of outdated PCs and thereby carry out a gradual upgrade of the computer system. Now the specifications for the 4th version of this data transfer method are being worked out. For graphics adapters in this case, a maximum of 128 GB/s will be provided. This will allow you to display the image on the monitor screen in “4K” quality or more.

Results

Be that as it may, PCI-E x16 is currently the only graphics slot and interface. It will be relevant for quite a long time. Its parameters allow you to create both entry-level computer systems and high-performance PCs with several accelerators. It is precisely due to this flexibility that no significant changes are expected in this niche.

Hello everyone who is interested in what a PCI slot is. I think there are many of them, because this standard is still used today, despite the release of modern analogues. If your computer is no longer young, most likely you are also dealing with PCI.

This article will help you understand its features and differences from the “Express” modification, which you may have heard about, since it is now widespread.

Introduction to the term

The abbreviation mentioned above stands for Peripheral component interconnect, which literally means the interconnection of peripheral components. Although this phrase does not reflect the physical embodiment of PCI, it was chosen for good reason.

As you understand, the “brain” of a computer includes different devices(audio Video-, network card etc.), so-called peripheral components. Most of them will connect to the motherboard.

For the connection between the devices and the motherboard, special electronic highways are used, in other words, buses. This is exactly what PCI is. In fact, this is a long expansion slot located on the motherboard into which a video card can be inserted, etc.

About the controller

There is also such a thing as a PCI controller Simple communications or Management Engine Interface, which ensures interaction between drivers of programs installed on the computer and motherboard drivers. Sometimes after reinstalling the system, a yellow triangle lights up next to this item in Device Manager.

In this case, you should download the drivers from the official Intel website or other reliable resource and install them. After all, this interface controls the temperature, rotation of coolers, sleep modes, etc.

Story

The PCI Special Interest Group, founded in 1992 under the leadership of Intel Corporation, is responsible for the creation and support of the interface. At the same time, its first version was published, released specifically to implement the functionality Pentium processors, Pentium Pro and 486.

The next year, the next model 2.0 appeared, and after another 3 years - 2.1, which was at the peak of popularity. True, after 2 years computer graphics went to new level, and PCI no longer meets its requirements. Then video cards began to be connected through a connector that was new at that time.

However, the interface we are considering did not lose its position until 2005. During this time, many generations of it have come out, but I don’t think you want to bother your head with them. Moreover, for the average user the differences between them are insignificant or incomprehensible.

PCI Specifications

Basic port parameters you should know about:

• Frequency - 33.33 or 66.66 megahertz, information is sent synchronously;
• Bit size - as usual, 32 or 64 bits;
• The address space of memory and I/O ports is the same - 4 bytes (32 bits);
• Another address space (configuration) per 1 function is 256 bytes;
• The maximum speed of the 32-bit and 33 MHz model is 133 megabytes per second;
• Voltage - 3.3 or 5 Volts;
• There is a Multiply bus master function, that is, several hard drive controllers can operate on the same bus at once.

Difference with PCI-Express

This is a modern modification of its predecessor. It is based on the PCI software model, but with significantly improved performance. Most devices are currently produced with this interface.

The first difference between them is that the outdated version is parallel, and the new one is sequential. This means that in the second case there is a bidirectional connection, which can include several lines (from x1 to x32). The more there are, the higher the speed of work.

Be that as it may, the throughput of a modern bus will be higher than that of its outdated counterpart. For comparison: PCI with a frequency of 66 MHz is 266 MB/s, and PCI-E 3rd generation with 16 lanes is 32 GB/s.

Now you know the basics about PCI.

I advise you not to dwell on this information and gain new knowledge from other articles on our blog.

The PCI Express standard is one of the foundations modern computers. PCI Express slots have long occupied a strong place on any desktop computer motherboard, displacing other standards, such as PCI. But even the PCI Express standard has its own variations and connection patterns that differ from each other. On new ones motherboards, starting around 2010, you can see on one motherboard a whole scattering of ports designated as PCIE or PCI-E, which may differ in the number of lines: one x1 or several x2, x4, x8, x12, x16 and x32.

So, let's find out why there is such confusion among the seemingly simple PCI Express peripheral port. And what is the purpose of each PCI Express x2, x4, x8, x12, x16 and x32 standard?

What is the PCI Express bus?

Back in the 2000s, when the transition took place from the aging PCI standard (extension - interconnection of peripheral components) to PCI Express, the latter had one huge advantage: instead of a serial bus, which was PCI, a point-to-point access bus was used. This meant that each individual PCI port and the cards installed in it could take full advantage of the maximum bandwidth without interfering with each other, as happened with a PCI connection. In those days, the number of peripheral devices inserted into expansion cards was abundant. Network cards, audio cards, TV tuners, and so on - all required a sufficient amount of PC resources. But unlike the PCI standard, which used a common bus for data transfer with multiple devices connected in parallel, PCI Express, when considered in general, is a packet network with a star topology.

PCI Express x16, PCI Express x1 and PCI on one board

In layman's terms, imagine your desktop PC as a small store with one or two salespeople. The old PCI standard was like a grocery store: everyone waited in the same line to be served, experiencing speed issues with the limitation of one salesperson behind the counter. PCI-E is more like a hypermarket: each customer follows his own individual route for groceries, and at the checkout, several cashiers take the order at once.

Obviously, a hypermarket is several times faster than a regular store in terms of speed of service, due to the fact that the store cannot afford the capacity of more than one salesperson with one cash register.

Also with dedicated data lanes for each expansion card or built-in motherboard components.

The influence of the number of lines on throughput

Now, to extend our store and hypermarket metaphor, imagine that each department of the hypermarket has its own cashiers reserved just for them. This is where the idea of ​​multiple data lanes comes into play.

PCI-E has gone through many changes since its inception. These days, new motherboards typically use version 3 of the standard, with the faster version 4 becoming more common, with version 5 expected in 2019. But different versions use the same physical connections, and these connections can be made in four main sizes: x1, x4, x8 and x16. (x32 ports exist, but are extremely rare on regular computer motherboards).

The different physical sizes of PCI-Express ports make it possible to clearly separate them by the number of simultaneous connections with motherboard: The larger the port physically, the more maximum connections it is capable of transmitting to or from the card. These connections are also called lines. One line can be thought of as a track consisting of two signal pairs: one for sending data and the other for receiving.

Different versions of the PCI-E standard allow you to use different speeds on every lane. But generally speaking, the more lanes there are on a single PCI-E port, the faster data can flow between the peripheral and the rest of the computer.

Returning to our metaphor: if we are talking about one seller in a store, then the x1 strip will be this only seller serving one client. A store with 4 cashiers already has 4 lines x4. And so on, you can assign cashiers by the number of lines, multiplying by 2.

Various PCI Express cards

Types of devices using PCI Express x2, x4, x8, x12, x16 and x32

For the PCI Express 3.0 version, the overall maximum data transfer speed is 8 GT/s. In reality, the speed for the PCI-E 3 version is slightly less than one gigabyte per second per lane.

Thus, a device using a PCI-E x1 port, for example, is low-power sound card or Wi-Fi antenna will be able to transmit data from maximum speed at 1 Gbit/s.

A card that physically fits into a larger slot - x4 or x8, for example, a USB 3.0 expansion card will be able to transfer data four or eight times faster, respectively.

The transfer speed of PCI-E x16 ports is theoretically limited to a maximum bandwidth of about 15 Gbps. This is more than enough in 2017 for all modern graphics cards developed by NVIDIA and AMD.

Most discrete graphics cards use a PCI-E x16 slot

The PCI Express 4.0 protocol allows the use of 16 GT/s, and PCI Express 5.0 will use 32 GT/s.

But currently there are no components that could use this number of lanes with maximum throughput. Modern high-end graphics cards usually use x16 PCI Express 3.0. It makes no sense to use the same lanes for a network card that will only use one lane on the x16 port, since the Ethernet port is only capable of transferring data up to one gigabit per second (which is about one-eighth the throughput of one PCI-E lane - remember: eight bits in one byte).

There are PCI-E SSDs on the market that support the x4 port, but they look set to be replaced by the rapidly evolving new M.2 standard. For solid state drives, which can also be used PCI-E bus. High quality network cards and enthusiast hardware such as RAID controllers use a combination of x4 and x8 formats.

PCI-E port and lane sizes may vary

This is one of the most confusing problems with PCI-E: a port can be made in the x16 form factor, but not have enough lanes to carry data through, for example, just x4. This is because even though PCI-E can carry an unlimited number of individual connections, there is still a practical limit to the chipset's bandwidth capacity. Cheaper motherboards with lower-end chipsets may only have one x8 slot, even if that slot can physically accommodate an x16 form factor card.

Additionally, motherboards aimed at gamers include up to four full PCI-E slots with x16 and the same number of lanes for maximum bandwidth.

Obviously this can cause problems. If the motherboard has two x16 slots, but one of them only has x4 lanes, then connecting a new graphics card will reduce the productivity of the first by as much as 75%. This is, of course, only a theoretical result. The architecture of motherboards is such that you will not see a sharp drop in performance.

The correct configuration of two graphics video cards should use exactly two x16 slots if you want maximum comfort from a tandem of two video cards. The manual at the office will help you find out how many lines a particular slot has on your motherboard. manufacturer's website.

Sometimes manufacturers even mark the number of lines on the motherboard PCB next to the slot

You need to know that a shorter x1 or x4 card can physically fit into a longer x8 or x16 slot. Contact configuration electrical contacts makes this possible. Naturally, if the card is physically larger than the slot, then you won’t be able to insert it.

Therefore, remember, when purchasing expansion cards or upgrading current ones, you must always remember both the size of the PCI Express slot and the number of lanes required.

When it comes to any interfaces in the context of computer systems, you need to be very careful not to “run into” incompatible interfaces for the same components within the system.

Fortunately, when it comes to the PCI-Express interface for connecting a video card, there will be practically no problems with incompatibility. In this article we will look at this in more detail, and also talk about what PCI-Express is.

Why is PCI-Express needed and what is it?

Let's start, as usual, with the very basics. PCI-Express (PCI-E) interface- this is a means of interaction, in this context, consisting of a bus controller and the corresponding slot (Fig. 2) on motherboard(to generalize).

This high-performance protocol is used, as noted above, to connect a video card to the system. Accordingly, the motherboard has a corresponding PCI-Express slot, where the video adapter is installed. Previously, video cards were connected via the AGP interface, but when this interface, simply put, “was no longer enough,” PCI-E came to the rescue, oh detailed specifications which we will talk about now.

Fig.2 (PCI-Express 3.0 slots on the motherboard)

Key Characteristics of PCI-Express (1.0, 2.0 and 3.0)

Despite the fact that the names PCI and PCI-Express are very similar, their connection (interaction) principles are radically different. In the case of PCI-Express, a line is used - bidirectional serial connection, point-to-point type, there can be several of these lines. In the case of video cards and motherboards (we do not take into account Cross Fire and SLI) that support PCI-Express x16 (that is, the majority), you can easily guess that there are 16 such lines (Fig. 3), quite often on motherboards with PCI- E 1.0, it was possible to see a second x8 slot for operation in SLI or Cross Fire mode.

Well, in PCI, the device is connected to a common 32-bit parallel bus.

Rice. 3. Example of slots with different numbers of lines

(as mentioned earlier, x16 is most often used)

The interface bandwidth is 2.5 Gbit/s. We need this data to track changes in this parameter in different versions of PCI-E.

Further, version 1.0 evolved into PCI-E 2.0. As a result of this transformation, we received twice the throughput, that is, 5 Gbit/s, but I would like to note that in performance graphics adapters, didn’t really benefit, since it’s just a version of the interface. Most of the performance depends on the video card itself; the interface version can only slightly improve or slow down data transfer (in this case there is no “braking”, and there is a good margin).

In the same way, in 2010, with a reserve, the interface was developed PCI-E 3.0, on this moment it is used in all new systems, but if you still have 1.0 or 2.0, then do not worry - below we will talk about relatively backward compatibility different versions.

With PCI-E 3.0, the bandwidth has been doubled compared to version 2.0. There were also a lot of technical changes made there.

Expected to be born by 2015 PCI-E 4.0, which is absolutely not surprising for the dynamic IT industry.

Well, okay, let's finish with these versions and bandwidth figures, and we'll touch on very important question backward compatibility of different versions of PCI-Express.

Backwards compatible with PCI-Express 1.0, 2.0 and 3.0 versions

This question worries many, especially when choosing a video card for the current system. Since being content with a system with a motherboard that supports PCI-Express 1.0, doubts arise whether a video card with PCI-Express 2.0 or 3.0 will work correctly? Yes, it will be at least This is what the developers who ensured this compatibility promise. The only thing is that the video card will not be able to fully reveal itself in all its glory, but the performance losses, in most cases, will be insignificant.

On the contrary, you can safely install video cards with a PCI-E 1.0 interface in motherboards that support PCI-E 3.0 or 2.0, there are no restrictions at all, so rest assured about compatibility. If, of course, everything is in order with other factors, insufficient powerful block food, etc.

Overall, we've talked quite a bit about PCI-Express, which should help you clear up a lot of confusion and doubt about compatibility and understanding the differences between PCI-E versions.

It uses two new operating frequencies: 100 MHz and 133 MHz. In addition, this bus implements a separate transaction mechanism in order to improve performance when multiple devices are connected at the same time.

Essentially PCI-X, which can be deciphered as PCI-eXtended, is a shortened version of PCI-E. Subsequently, the expansion was supplanted by its more compact counterpart, as space on the motherboard became an increasingly pressing issue, “motherboards” became smaller, which required the same from the slots. So PCI-E almost completely replaced PCI-X.

For the PCI-X bus, there are restrictions on the number of devices connected to it: 66 MHz - 4, 100 MHz - 2, 133 MHz - 1, 2, 266 and 533 MHz - only 1.

This bus is compatible with all 3.3V and universal PCI expansion cards. Generally, PCI-X is not widely used on modern motherboards. In the professional segment it is used for RAID controllers, in SSDs, under PCI-E.

PCI-X was developed in collaboration between IBM, HP and Compaq. The tire appeared on the market in 1998. The main purpose of creating a new tire was an attempt to introduce a codified various extensions on the local platform PCI new a bus that would eliminate the disadvantages of PCI, would be faster and more productive, and at the same time would increase the popularity of devices such as: Gigabit Ethernet, Fiber Channel and Ultra3 SCSI cards. PCI-X is disconnected from other PCI buses and allows different agents to use it. Split responses increase bus efficiency by eliminating repeated loops during which data cannot be transferred on the bus. In addition, PCI-X added MSI devices, interrupting the system by writing to host memory.

Theoretically, the maximum amount of data transferred between the processor and peripheral devices using PCI-X is 1.06 GB/s, compared to 133 MB/s for standard PCI. PCI-X also has an improved level of fault tolerance, allowing the user to, for example, reinitialization faulty card or take it offline.

PCI-X is not compatible with the old 5V I/O that was so widely used in standard version PCI.

What is the difference between PCI-X and PCI 64?

A 64-bit PCI slot is distinguishable from a 32-bit one by its length, first of all, and it differs from PCI-X by the presence of three segments, with one in the middle, which is much shorter than the others. PCI-X slots can be distinguished from PCI 64 by a small segment at the beginning, the same small one in PCI 64 is located in the middle of the slot. This is about visual differences.

A 32-bit card will function properly on a PCI-X slot, but PCI-X cards will not work on a 32-bit slot. Some PCI 64 cards can function normally on 32-bit slots, but with the inevitable double power loss, since the bus bandwidth is lower.

Versions:

Cards

• 66 MHz
• 100 MHz
• 133 MHz
• 266 MHz
• 533 MHz

Slots

• 66 MHz
• 133 MHz
• 266 MHz
• 533 MHz