PCI vs. PCI Express: Difference Between Conventional Slots


By Jack

Update on

PCI vs. PCI Express

We have covered the basics of the difference between PCI vs. PCI Express, functions, compatibility, appearance, and speed.

We have distinguished between these two conventional slots based on these four aspects. Read further to learn more about this topic.

Brief Introduction of PCI and PCIe

In computers, data is exchanged via certain channels known as a bus. The bus is considered a common linking trunk line to exchange information between different devices on a PC.

It is made up of wires and is used for transmitting data from one functional part of the computer to another. Both PCIe and PCI are buses.

The principle work of both slots is the same. However, on other aspects, you know the difference between PCI vs. PCI Express.

PS: let’s learn more about the different types of motherboard form factors you should know here.

What is the Role of PCI in a Computer?

PCI is the acronym for Peripheral Component Interconnect, a local bus in your operating system. So how does this local bus work? Let’s heads on further to know the detail about this slot. 

From 2000 to 2010, the structure of the motherboard was like a North-South Bridge chip that relies on PCI. Northbridge chip and CPU are both connected through FBS (Front Side Bus).

The main responsibility of the Northbridge chip is to control the exchange of data between the CPU and other high-speed functional devices (memory card, AGP graphic card).


On the other hand, the Southbridge chip is linked with the Northbridge chip through an inner bus (for example, Hub-Link).

On the contrary, the Southbridge chip is used for controlling the exchange of data between CPU and low-speed functional devices like keyboards, add-in cards, and hard disks.

Now, if you have a question, where is PCI located on the computer? Then let us tell you it is located under the Southbridge chip.

There are different buses under the Southbridge chip, like PCI, USB, SATA, LPC, Low Pin Count, etc. LCP bus is used to link the other low-speed devices such as a mouse, keyboard, floppy, BIOS, etc.

What is the Role of PCI Express in PC?

First, let’s see what PCI Express is. It is also denoted as PCI-E/PCIe, which is the new version of AGP and PCI. Plus, it is slowly occurring on USB and SATA buses. In the PCIe motherboard, the Northbridge chip is directly linked to the CPU.  

PCI Express

Similar to this, memory cards and graphics cards are also connected to the CPU. However, there are two important points that you must consider.

Firstly, the connection between the graphics card and CPU is through a PCI-E bus. Secondly, the direct link between PCI-E SSD and CPU is supported by the motherboard. PCI vs. PCI Express is different in terms of structure and model.

In case you have an Intel Z390 motherboard, then its chipset (Southbridge) is directly connected to the CPU through DMI or Direct Media Interface 3.0 bus. This version of the bus relies on the PCI-E bus.

The Southbridge is responsible for the distribution of 24 PCI-E lanes, which are used for linking USB devices, audio cards, hard drives, network cards, etc. This indicates that PCI-E is not a local bus. It’s a sophisticated system bus. 

If you are thinking about M.2 PCI-E SSD, then you must consider the two below conditions.

  • The graphic card of the computer system uses PCI-E 3.0*8 lanes, and the remaining two PCI-E ports need to insert 2NMe SSDs. In such a situation, there is a direct connection between SSDS and CPU. It allows each SSD to exclusively get 4 GB/s throughput.  
  • The graphic card of your computer system uses PCI-E 3.0*16 lanes, and on the other hand, the M.2 PCI-E SSD shares 24 PCH/ICHPCI-E lanes with different devices. Plus, it limits SSD speed by DMI 3.0 (when DMI speed 3.0*4 equals that of PCI-E 3.0*4). This is the main reason why M.2, U.2, and Thunderbolt interfaces are not efficient enough to replace the PCI-E*4 bandwidth.

Your system will use the second design most of the time. The speed of PCI-E SSD is quicker as compared to other SSDs, such as SATA, even though it shares throughput with different devices.

Also, devices on the Southbridge chip do not operate together, so the DMI 3.0 throughput is enough.

Here, we have covered a direct comparison of PCI vs. PCI Express from three aspects. Read further to learn about the difference between PCI vs. PCI Express. 

PCI vs. PCI Express: Form Factors and Slots

The structure of PCI and PCIe is different from each other. In the case of a PCI slot, there are two types: One is a 32-bit slot having 124 pins, and the other is a 64-bit slot having 188 pins. The 32-bit slot is used in common computer systems, whereas the 64-bit slot is used in servers.

PCI vs. PCI Express Slot

Let’s move on to another slot which is the PCIe slot. There are seven different versions in the PCIe slot, that are, x1, x2, x3, x4, x8, x12, x16, and x32 and /1, /2, /3, /4, /8, /12, /16, and /32 respectively.

Among these, the smallest version of PCIe is x1 in size, and the largest one is x32. This is the main reason why x32 is not used often; plus, the lack of corresponding large production products makes it harder to use x32 for general work.

PCI-E x12 is employed in servers and does not display on customer platforms. PCI-E x2 is commonly employed for internal interfaces instead of expansion slots. Although few motherboards incorporate this interface, PCI-E x2 is displayed as M.2 interface rather than a PCI-E slot. 

There are Four Types of Conventional PCI-E Motherboard Slots.

They are PCI-E x1 / x2 / x8 / x16. Learn each of them thoroughly. 

  • PCI-E x16 slot: PCI-E x16 is 89 mm long and incorporates 164 pins. It’s majorly used for graphic cards as well as backward compatibility along with x1 / x4 / x8 accessories. 
  • PCI-E x8 slot: PCI-E x8 slot is 56 mm long and incorporates 98 pins. Although it is displayed as a slot of PCI-E x16, just half of the data pins of this slot are valid. This indicates that the bandwidth of this slot is half of the slot of PCI-E x16. It is mostly used to install graphic cards on the PCI-E x8 interface with the help of the PCI-E x16 interface.
  • PCI-E x4 slot: PCI-E x4 slot is 39 mm long and incorporates 64 pins. It allows you to install M.2 SSDs or PCI-E SSDs (with the help of PCI-E adapters). When this slot leaves the factory, it comes more like an interface of M.2.
  • PCI-E x1 slot: It’s the shortest slot among all. It is 25 mm long and incorporates 36 pins. The target products are expensive, including USB 3.0/3.1 expansion cards, independent sound cards, independent network cards, etc.
Four Types of Conventional PCI-E Motherboard Slots

PCI vs. PCI Express: Speed Comparison

Here, we will explain to you PCI vs. PCI Express speed. We have already covered the difference in speed between these slots. In this part, you will learn the reason why the PCIe interface replaced the PCI interface. 

The speed of PCI of 32-bit is around 133 MB/s, and the speed of PCI of 64-bit is around 266 MB/s. The PCI speed depends on versions and lanes, which is why each version’s correspondence to its lane varies from one another.  

PCI vs. PCI Express Speed

Most computers use PCI-E 3.0 edition at present. This version enhances the speed of the slot, and even x1 becomes quicker as opposed to 64-bit PCI. In PCI vs. PCI Express speed, PCI Express is the best choice. 

PCI vs. PCI Express: Compatibility Differences

There is quite a difference between PCI vs. PCI Express incompatibility. The compatibility of PCI technology over various hardware devices is exponential. However, the only problem with this slot was it was neither backward nor forward-compatible.

This means that you cannot use one port of the PCI version for another PCI. With the help of notches, the PCI slot prevents the connection between other PCI versions.

PCI vs. PCI Express Compatibility

On the other hand, PCIe eliminates this problem. All the versions of PCIe and its ports are backward and forward-compatible. You can easily connect any PCI port with any of the PCI counterparts.

This happens because the structure of all PCI ports is the same, and it enables any devices to be easily connected. There are a lot of open-ended PCI-E parts where you can fit any size of slot, big or small.

PCI vs. PCI Express Compatibility

You can use the advanced device with the old version of PCI-E, but the bandwidth will decrease to the level of the PCIe versions you are using. It is similar to the reverse method.

If you connect old devices with the latest version of the PCIe slot, the bandwidth will not increase. However, you can attach any device to any PCIe slot. This is why the company prefers PCIe.

Even though PCIe is compatible with all PCIe versions or generations, it is not applicable for PCI or PCI-X or any other type of PCI-E interface. 

How to Transfer PCI vs. PCI Express Connector Expansion Slot?

The methods used to connect the slots to the devices are different in both PCI and PCI-E. The method that PCI use is known as the parallel interface method.

On the other hand, PCI-E uses a series method. Both methods give different connectivity experiences.  

The parallel method in PCI transfers a huge amount of data into small groups or packs and sends them via connectors simultaneously at once. PCI-X follows the same method.

The data is transferred via slot lanes simultaneously, which also causes bottlenecking when different devices work at their peak at once. It used to hamper the data transfer process a lot.

The PCI-E slots did not have a data transfer problem because it uses the series method. The series method allows each device its bus or lane in a system. Unlike PCI, the size of data is fixed in series.

This enables the PCI-E slot to encounter a lower interface in comparison to the PCI interface. This method automatically solves the bottleneck problem which you may find while using the PCI slot.

The speed of every data transfer is the same, and it does not hamper the process. In PCI vs. PCI Express compatibility, the PCI Express slot once again exceeds to PCI slot. 

FAQs (Frequently Asked Questions)

1. Can I use a PCI card in a PCIe slot? No, PCI and PCIe are not compatible with each other. PCI cards can only be used in PCI slots, while PCIe cards require PCIe slots for proper operation.

2. Are all PCIe slots the same? No, PCIe slots come in different sizes and configurations, including x1, x4, x8, and x16. The number indicates the number of lanes available for data transfer.

3. Can I install a PCIe x16 card in a PCIe x1 slot? In most cases, it is not possible to install a PCIe x16 card in a PCIe x1 slot due to physical limitations. However, some motherboards may have PCIe slot adapters that allow for such installations, albeit with reduced performance.

4. Which is faster, PCIe 3.0 or PCIe 4.0? PCIe 4.0 is faster than PCIe 3.0, offering double the bandwidth per lane. This results in higher overall data transfer speeds and improved performance for devices that support PCIe 4.0.

5. Can I mix PCI and PCIe cards in the same system? Yes, it is possible to have a combination of PCI and PCIe cards in the same system as long as the motherboard provides the necessary slots for both standards.


In this article, we have covered all the important points of both slots to understand the difference between PCI vs. PCI Express.

Although the work that both slots deliver is the same, however, the method used by them is different. PCIe is advanced and has outperformed PCI technology.    


Ten years of experience in information and computer technology. Passionate about electronic devices, smartphones, computers, and modern technology.