PCI vs PCIe | Direct Comparison Between Conventional Slots

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PCI and PCIe are among the two most popular methods of connectivity for a long time. Both of them operate under the same protocols, but there are many dissimilarities between them. In this article, we’re going to discuss the overview and direct comparison between the PCI vs PCIe slot. So, PCI or PCIe? Which one is better? By the end of this article, you will know all about it.

PCI vs PCIe Fi


PCI vs PCI-E By Definition

PCI means “Peripheral Component Interface” (or, Interconnect). So, what is PCIe? PCIe is also known as PCI-Express (Peripheral Component Interface Express). PCIe vs PCI vary in many sectors. 2 main variants of PCI technology are the PCI-X and AGP ports. AGP ports were used for video cards, and PCI along with PCI-X was used for all the other applications. They follow industry-standard architecture (ISA).

By Definition

PCIe is a major upgrade from them because it supports almost all the hardware components, including modern graphics cards too. So, we don’t need dedicated slots for graphics cards as long as we have supporting PCIe ports.

By Definition 2

PCI vs PCIe in Working Topology

PCI works in parallel transmission mode, but PCI Express works in serial transmission mode. In parallel transmission mode, there is a huge possibility of data corruption and so the increment of frequency is not possible at all. As a result, the bandwidth can be increased effectively. That’s why PCI Express has arrived.

Devices are connected directly through the main bus of PCI, but in the case of PCI Express, this one has a switch to control the connection of different devices. PCI Express provides a high-speed serial connection. It can handle multiple data sources like a network card.


PCI slots are the direct descendants of PC-XT and PC-AT slot technologies which were much popular in the 90s but lost their value in modern data transfer needs. PCIe slot or PCI Express interface, on the other hand, is an upgraded version of the PCI interface itself. Although the key difference in origin, PCI and PCIe are applied in roughly the same fields, to add more expansion slots like PCI x slots in a motherboard. You can check available slots on the motherboard by checking its model.

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PCI vs PCIe Compatibility

A big reason to use PCI technology is its compatibility over a vast portion of hardware devices. But one major problem was, PCI was neither forward nor backward compatible, meaning you can’t use one PCI version port to another PCI slot. Some universal PCI were excluded from this problem. PCI slots use notches to physically prevent other versions to be attached.


On the contrary, PCIe has a major advantage in this matter. All PCIe slots and ports are forward and backward compatible. Any PCIe port can be used with any other PCIe counterparts. For this reason, the structure of all PCIe slots is the same, which allows any type of device to be connected. There are many open-ended PCIe slots too, where one side of the slot is open to fit bigger ports inside.

Compatibility 2

Although a more upgraded device can be used in previous PCIe versions, the bandwidth will drop to the level of the previous versions. The same goes for the reverse methods. Attaching a previous generation device to a new generation PCIe slot will not increase its bandwidth, but the device will support the PCIe slot nonetheless. Note that, although PCIe is compatible with its previous and next PCIe generation/versions, it isn’t compatible with PCI and PCI-X slots or any type of PCIe interface.

Method of Data Transfer in PCI vs PCIe Connector Expansion Slot

Another big difference between PCI and PCIe is their methods of connectivity. PCI slots use a parallel interface method, whereas PCIe device technology uses a series method. The connectivity experience varies between these two forms.

For PCI slots, parallel transfer works by dividing a large amount of data into small packs or groups, and then sending them through the connectors at once parallelly. PCI-X also works on this basis. Data is transferred simultaneously through the slot lanes, which causes bottlenecking when multiple devices operate at their peak performances. As a result, data transfer hampers.

PCIe slots use the series connection, where each and every device can get its own lane or bus in a system. PCIe slot transfers data in a fixed size in series, unlike PCI where multiple lanes of data are transferred at once. As a result, PCIe slots can encounter relatively lower interference, hence the bottlenecking problem is solved. Every transfer achieves the same clock and rate and isn’t hampered by each other. You may have seen this difference already if you are familiar with using PCIe SSD and SATA SSD or Serial Ata SSD. The SATA interface speed is comparatively low than the PCIe bandwidth.

Here is the Samsung M.2 NVMe SSD having a huge storage capacity of 1TB which we think is more than enough as an SSD expansion card.

Method of Data Transfer
Method of Data Transfer 2

PCI vs PCIe Speed

There are two versions available in PCI. They are 32-bit PCI Bus and 64-bit PCI Bus. The 32-bit older PCI version runs at 33MHZ and the 64-bit PCI Bus version runs at 66MHZ. In 32 bit, the supplied bandwidth by PCI is 133 MB/s and this version is used for computers only. The other 64bit supplies 266 MB/s and this one is used on servers. If you look at the bandwidth of PCI Express or PCIe bus, you will have no doubt why PCI Express is in demand in terms of PCI vs PCI express. There are several numbers of PCI Express version or PCIe interface. So have a look at the following table below.

So the speed is way fast than the PCI. In case of using a graphics card or any high bandwidth required devices, PCI Express is a must to use.

Different Versions

PCI and PCIe also differ a great deal among their respective versions. PCI technology has different versions based on clock speed, voltage, and transfer rate. Coming from the 90s PC-XT and PC-AT slots, version-wise PCI slots are different and not forward or backward compatible. The notch between the buses kept them from mixing up in other version slots. PCI 1.0, PCI 2.0, PCI 2.2 are some of the most popular models used by consumers. Another specialized version is used as AGP and AGP Pro slots dedicated to video cards. A lot of space wastage occurred due to the compatibility issues caused by hardware components with different PCI versions.

PCIe on the other hand uses lane numbers to differentiate between versions. As a serial connector, PCIe utilizes data traffic lanes instead of quantity. Throughout the versions, the unit data transfer per lane is increased a bit, and also the number of series of data can be transferred at a time.

Different Versions
Different Versions 2

PCIe x1 slot is the simplest and smallest slot that transfers 1 series of data. PCIe x4 is the second version with 4 series of data transfers at a time. PCIe x8 is the third variant, and PCIe x16 slot is usually used by modern GPUs.

Different Versions 3

PCIe can boast a larger transfer rate due to the series connection. PCIe 1.0 has 250MB/s data transfer rate per lane, PCIe 2.0 has 500MB/s, and PCIe 3.0 has 985MB/s. This transfer rate rises significantly along with the rise of lanes (x1 slot, x4, x8, x16 slot). The PCI Express x16 has an enormous transfer rate. Another advantage is, all the PCIe ports are structurally the same, only longer or shorter, and any version can be used in any slot. All ports will be compatible but will run at the lowest allowed speed.

Release and Timeline

PCI has become an old method of the interface, and can’t be seen nowadays except in very old computers. But PCIe slots are used everywhere now. PCI 1.0 launched first in 1992, whereas PCI Express launched in 2003. For the high level of compatibility and transfer rate, PCIe is still widely used in almost all computer motherboards because it supports almost all hardware components released at present. Many users upgrade their motherboards for this updated PCIe gen. PCI slots, on the other hand, are soon going to be extinct.

GPU Connection Arrangement

Here we will discuss PCI vs PCIe x16. In the old PCI slots, a graphics card couldn’t be attached. Specialized version of PCI, the AGP and AGP Pro slots were used for this purpose. However, modern PCIe x16 is used for newer graphics cards. The advantage here is, we can still use PCIe x16 for other applications except only in graphics cards. These are the longest form of PCIe with the highest data transfer rate, which is essential for graphics cards.

GPU Connection Arrangement
GPU Connection Arrangement 2

Do you have a plan to buy the latest GPU from Nvidia? If you are a gamer or a graphics designer, this will be the best choice for you.

PCI vs PCIe in Hot Plugging

A total number of 32 end-point devices can be connected to the PCI Express. PCI Express handles hot plugging. But this hot-plugging feature is not available in PCI. They can handle rarely a maximum of 5 devices.

Overall Better Deal

The overall better choice among PCI and PCIe is obviously the last one. Not only PCIe can transfer data much faster because of its serial connection as opposed to the parallel one in the PCI slot, but also PCIe slot is much more compatible than PCI slots. PCIe are both forward and backward compatible, where PCI isn’t. Modern hardware components mostly come with PCIe supported ports, so buying a motherboard with a PCI slot or PCI ports can render it useless now.


1.Which one is fast between PCI and PCI Express?

The speed of PCI Express is faster than the bandwidth of PCI speed. If you take an example of PCI Express x1 bandwidth, this is 118% faster than the conventional PCI’s bandwidth. If you look into the video cards of these, you will find out PCI Express’s video card’s bandwidth is almost 29% faster than the bandwidth video card of PCI.

2.What is meant by a PCI Express slot and PCIe card?

The physical size of PCI Express is known as the PCI-e slot. It has four types of slots. They are x16, x8, x4, x1. The greater number indicates the larger size of the PCI Express and it makes it the winner between PCI slot vs PCIe. And the PCIe cards are compatible with PCIe card Slots.

3. Does the PCI card work perfectly in PCI Express slots or can you put a PCI card in PCI Express slot?

No, this is not the right use of PCI cards in PCI Express slots. On the motherboard, there are different places for these. So PCI Express slots are only compatible with PCI Express not for PCI cards and this PCI and PCIe difference makes a huge impact on the technology.


In this article, we briefly discussed the main differences between PCI vs PCIe technology. While both of them work on the same principle and for the same purposes, PCIe is the modern PCI standard that outperforms the old PCI technology in almost every way. A motherboard with a higher number of PCIe ports can be a great choice for further upgrading and utilization. We hope that now you know all about the difference between PCI and PCIe.

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