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The difference between PCI and PCI Express
2017-01-17
PCIe PCI Express

The Peripheral Component Interconnect or more commonly known as PCI is a standard for connecting a lot of devices inside your computer to extend its capabilities. Devices like sound cards, modems, NIC, TV Tuners, and some video cards have at some point or another have used the PCI port. The latest version of PCI known as PCI express is a much improved version in terms of speed. So what is the difference between PCI and PCI Express? For answering this question, you need to know the definition of them firstly.

What is PCI?

PCI stand for Peripheral Component Interconnect, it is a parallel bus, synchronous to a single bus clock. Attached devices can take either the form of an integrated circuit fitted onto the motherboard itself (called a planar device in the PCI specification) or an expansion card that fits into a slot.

PCI

What is PCI Express?

PCI Express, namely the network card of PCI Express slots, is the network components that works in the data link layer, and is an interface that connects the computer and the transmission media in the LAN.
PCI Express

How do they differ?

Type of interface
PCIe uses a serial interface while PCI uses a parallel interface. It also utilizes individual buses for each of the devices connected to it instead of a shared one like what PCI uses. The difference in speed is quite huge when comparing the standard PCI slot which runs at 133MB/s to a 16 slot PCIe that can send or receive up to 16GB/s.
Use of PCIe
The most common use for PCIe nowadays is with graphics cards which benefits hugely from the huge bandwidth provided by the interface. PCIe has totally replaced another standard called AGP which was specifically intended for graphics cards.
PCIe speed is classified into lanes, each capable of delivering up to 1GB/s data transfer
PCIe wasn’t intended to run at full speed for all devices since most devices don’t really need that much to operate properly. Speeds are categorized by lanes, each with its own transmit and receive lines. Each lane can provide up to a maximum of 1GB/s, thus giving the 16 lane slot the maximum 16GB/s, slower devices are categorized by the number of lanes they use from 1 to 16. 
PCI slots are standardized while PCIe slots vary depending on the number of lanes.
Unlike PCI slots which are the same size for all devices, PCIe slots can differ depending on which form factor it accepts. The longest would be the 16 lane slot and understandably, the shortest is for the x1 devices. Although there are slots that accept multiple form factors but only operate at a lower speed. This is done in order to allow the use of bigger cards in what would otherwise be a smaller slot. Even if the speed doesn’t necessarily match up to what is required, it allows the user a little bit more flexibility in terms of what he can plug into his machine.
PCI vs PCIe

Are PCI and PCIE cards interchangeable?

They both possess different connection methods and even though they both possess “Peripheral Component Interconnect” in their individual names, they are still two major different technologies. They both possess backward- compatible and forward-compatible revisions for their individual port types and these can’t be interchanged.

Difference between PCI and PCI express :

 
S.NO PCI PCI express
1. PCI is a computer bus that connects hardware devices. An advanced version of PCI bus that connects graphic ports, Wifi and other devices.
2. It was introduced in the year 1992 by Intel. It was introduced in the year 2003 by Intel, Dell and other organizations.
3. It is a parallel bus interface It is a serial bus interface.
4. Conventional PCI is the other name for PCI. PCI-e is the abbreviated name for PCI Express.
5. It works slower. It works faster.
6. PCI provides a slower data rate PCI Express provides faster data rate.
7. The PCI slots are standardized The PCI-e slots depends upon number of lanes.
8. The speed of a PCI slot is upto 133MB/s. The speed of a PCI-e slot is upto 16 GB/s.
9. It has less features. It has more features.
10. It may or may not have hot swapping feature. It has the hot swapping feature.

PCI Special Interest Group (PCI-SIG):

PCI-SIG defines and maintains the technical specifications and standards for PCI and PCIe. PCI-SIG is a special interest group of 900 companies. It defined PCIe in 1995 as PCIe 1.1. Since then, it has developed four versions of PCIe standards for improved architectures. PCIe supports high data throughput, low power and is of smaller size. PCIe makes today’s laptops, computers smaller, making them powerful, portable, and handy. Lanes in PCI-e are many interfaces on which data transfers can happen in parallel. Laptop expansions, computer storage interfaces like SATA express use PCI-e with many lanes. Table 1 shows the PCIe architectures and their bandwidth details:

Table 1 PCIe architectures and their bandwidth details

PCI vs PCIe Compatibility

In terms of compatibility, there are several points you should remember:

  1. PCI:The 32-bit PCI interface is not compatible with 64-bit PCI products, while the 64-bit PCI interface is compatible with 32-bit PCI products.

  2. PCIe:PCI-E interfaces have different lengths. The more lanes it has, the longer the interface. Generally, long slots are compatible with short interface products. For example, PCIe X16 slot can be compatible with X4 or X8 products. But short slots cannot be compatible with long interface products because they cannot be inserted.

  3. PCIe:PCIe has different versions. Different versions are compatible with each other. For example, PCIe 3.0 is compatible with PCIe 2.0. But the performance is determined by the low version.

  4. PCI vs PCIe:The PCI-E interface and the PCI interface are not compatible with each other.

Summary:

Although PCIe is generally superior compared to PCI, and PCIe is much faster compared to PCI, there is still a lot of devices that are being made for the PCI slot, due in part to the simplicity of PCI and to the fact that most devices do not really need the significant speed advantage.
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