What is PCI chips, PCIe Chips, PCI slots, types, and its functions

👤 Diwas Poudel    🕒 Oct 24 2020    📁 Fix    📜 0 comment

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The motherboard is one of the important parts of the computer. It consists of various types of components among them PCI slots and chip is one of them. It is one of the useful components of the Motherboard. It is used for various devices like modems, TV cards, memory, hard drive controller, I/O ports, sound cards, Graphics cards, USB, Coprocessors, network cards.

Evolution of PCI and PCIe

Expansion slots like PCI have around 5 decades-long histories. Altair 8800 was the first slot-type expansion card bus added to a microcomputer in 1974-1975 which is located on the back panel of the PC. Later IBM develops ISA on IBM PC XT of 4.77 MB/second. Later in 1984, 16 bit ISA was developed with the bandwidth of 8 MB/second. Then MCA slots were developed but due to licensing all pc manufacturers cannot use it. Then came EISA but its speed cannot extend more than 8 MB/s. Then came VLB but due to compatibility with 486-class processors only cannot extend further and cannot supports to Pentium processor. Then first industrial standard expansion slot named PCI appeared in 1992 by Intel. Many companies joined the alliance which is known today as PCI-SIG(PCI Special Interest Group). The standardization of the PCI, PCI-X, and PCI Express slots is the responsibility of the PCI-SIG.


PCI stands for Peripheral components interconnect. From this full form, it is clear that external hardware components are interconnected and make it working with other components by coordinating each other. When we talk about PCI then it includes both PCI slots on the motherboard and PCI chips itself.

It's smart idea to pick wider case having a sufficient number of PCI expansion slots when buying computer. So  If you want to connect some cards later, such as wireless card, hard disk controller, USB slots, or TV tuner,  this will surely be helpful.

PCI bus Architecture

PCI bus architecture is a processor-independent bus that allows peripherals to access main memory directly without CPU.So, this helps to free up the CPU for doing other works.PCI simply takes the help of a bridge chip to access the system. Here, the bridge acts as a translation of transaction from CPU bus to PCI bus

The function of PCI and PCI Express 

Suppose your ethernet card is not working then you can add an ethernet expansion card in PCI slots and enjoy it.


Types of PCI Slots and PCI Chips

PCI slots are divided into 3 categories ie. PCI, PCI-X, and PCIe. They are divided on the basis on two main factor.

a) Bus Width: 32 bit or 64 bit

b) Signal Voltage : 3.3 V or 5 V

Different types of PCI slots are listed below:

  • PCI Slot
  • PCI-X 66
  • PCI-X 133
  • PCI-X 266
  • PCI-X 533
  • PCIe 1.0 x 1  , PCIe 1.0 x 4 , PCIe 1.0 x 8 , PCIe 1.0 x 16  
  • PCIe 2.0 x 1 ,PCIe 2.0 x 4 , PCIe 3.0 x 8 , PCIe 2.0 x 16  
  • PCIe 3.0 x 1 ,PCIe 3.0 x 4 , PCIe 3.0 x 8 , PCIe 3.0 x 16 
  • PCIe 4.0 x 1 ,PCIe 3.0 x 4 , PCIe 4.0 x 8 , PCIe 4.0 x 16 
  • PCIe 5.0 x 1 ,PCIe 3.0 x 4 , PCIe 5.0 x 8 , PCIe 5.0 x 16 
  • PCIe 6.0 x 1 ,PCIe 3.0 x 4 , PCIe 6.0 x 8 , PCIe 6.0 x 16 

PCIe is an extended version of PCI called PCI-Express.

 1) Conventional PCI

1. a. PCI Slot with 5 V signaling

This is the first version of PCI which operates at 33 MHz bus clock using a 32-bit wide path and its bandwidth is 133 MB/s. Its signal voltage is 5 V.

Then 64-bit operating on 66 MHz with bandwidth = 133 MB/s was also developed operating on 5 V.

1 b. PCI Slot with 3.3 V signaling

Both 32-bit(33 MHz, 133MB/s) and 64-bit version(66 MHz,133 MB/s) of 3.3 V was developed.

💡 The PCI slot is also known as Conventional Slot.

At that time there is a problem and the problem is the PCI slot with 5V does not fit in the 3.3 V slot and vice versa. So, a universal PCI slot was developed.

1 c. Universal (3.3 V and 5 V) 32 bit PCI card 

This supports both 3.3 V and 5 V of 32 bit PCI Card. So, even if a 3.3 V 32 bit PCI Card is inserted into a Universal 32 bit slot then still it will work

1 d. Universal (3.3 V and 5V) 64 bit PCI card

This supports both 3.3 V and 5V of 64-bit PCI card. So, if 3.3 V 64 bit PCI card is inserted into a Universal 64 bit slot then still it will work.

💡  3.3V only PCI  cannot be plugged into a PC's 5V-only PCI.

Most of PCI available in the market are 32 bit PCI.

So, the maximum speed of PCI slot (3.3 v or 5 v) cannot exist 133 MB/s and this didn't meet the requirements of modern PCs.So, PCI-SIG developed a new standard called PCI-X.

 2) PCI-X

PCI-X stands for PCI-eXtended. The number after X denotes indicates the operational frequency of PCI.

a. PCI-X 66

This version of PCI operates at 66 MHz bus clocks using a 64-bit wide path and its bandwidth is 533 MB/s. Here data per clock cycle is 1.

b. PCI-X 133

This version of PCI operates at 133 MHz bus clocks using a 64-bit wide path and its bandwidth is 1,066 MB/s. Here data per clock cycle is 1.

c. PCI-X 266

This version of PCI operates at 133 MHz bus clocks using a 64-bit wide path and its bandwidth is 2,132 MB/s. Here data per clock cycle is 2.

d. PCI-X 533

This version of PCI operates at 133 MHz bus clocks using a 64-bit wide path and its bandwidth is 4.266 MB/s. Here data per clock cycle is 4.

3) PCI-Express (PCIe)

This version of PCI is constantly replacing PCI as the default expansion slot for add-in cards.

PCIe Types Clocks Wide Path Bandwidth
PCIe 1.0 x 1 2.5 GHz 1 bit 250 MB/s
PCIe 1.0 x 4 2.5 GHz 4 bit 1000 MB/s
PCIe 1.0 x 8 2.5 GHz 8 bit 2000 MB/s
PCIe 1.0 x 16 2.5 GHz 16 bit 4000 MB/s
PCIe 2.0 x 1 5 GHZ 1 bit 500 MB/s
PCIe 2.0 x 4 5 GHz 4 bit 2000 MB/s
PCIe 2.0 x 8 5 GHz 8 bit 4000 MB/s
PCIe 2.0 x 16 5 GHz 16 bit 8000 MB/s
PCIe 3.0 x 1 8 GHz 1 bit 1000 MB/s
PCIe 3.0 x 4 8 GHz 4 bit 4000 MB/s
PCIe 3.0 x 8 8 GHz 8 bit 8000 MB/s
PCIe 3.0 x 16 8 GHz 16 bit 16000 MB/s

Data Transfer in PCI 

1) Conventional PCI and PCI-X

In older PCI like Conventional PCI and PCI-X data transfer in a parallel mode where several bits of data are transferred at the same time.

2) PCI-Express 

In the latest version of PCI like PCIe, data transfer is in a serial mode where a single bit of data transferred at the same time. 

As we know that the parallel mode of data transfer is faster than the serial mode, then why the latest PCI adopted serial mode?🤔🤔🤔🤔🤔.If the same questions raise in your mind then here is an answer.

➤ The modern motherboard is operating its task at a high frequency so, to get maximum benefits of the motherboard, a high-frequency PCI slot like PCIe is used. And PCIe uses a serial mode of data transfer. If data transfer in PCIe is the parallel mode then at high frequency large electromagnetic interference occurs which induce an electric current in an adjacent wire and induce current oppose the data transfer and data loss may occur.

Suppose, there are 32-bit PCIe slots and data transfer 32 bit at a time(parallelly) in 32 wire so, if higher the clock more interference occurs and data transmission loss may occur.  

Propagation delay is also the problem. Every bit transmits on a different wire in parallel mode of communication, but it's nearly impossible to make the 32 wires on a motherboard exactly the same length. At higher frequency, data transmitted by shorter wire arrive earlier than from longer wire to the receiving devices. So, receiving devices have to wait for all bits of data to arrive in order and this increased delay in the system and will be even worse if data transfer at high frequency.

So, in most of the high-frequency components like PCIe, serial communication is used. The negligible delay occurs but will guarantee data transfer.

Also, serial communication is preferred because, in serial, full-duplex(one set of wires to transmit data and another set of wires to receive data) communication is possible so sending and receiving devices can communicate at the same time but in parallel only half-duplex(same wires/path for receiving and sending data) is possible so in parallel two devices cannot communicate at the same time. Therefore, serial communication is preferred.

At lower frequency, serial communication seems to be faster so, Conventional PCI uses serial Communication. At higher frequency, parallel communication is preferred.