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Types of Computer Buses

Patrick, a computer technician, is a dedicated writer who wishes to make the world better by informing individuals who seek more knowledge.

Inside computers, there are many internal components. In order for these components to communicate with each other, they make use of wires that are known as a ‘bus’.

A bus is a common pathway through which information flows from one computer component to another. This pathway is used for communication purposes and it is established between two or more computer components. We are going to check different computer bus architectures that are found in computers.

Different Types of Computer Buses

The Computer Buses

The Computer Buses

Functions of Buses in Computers

Summary of functions of buses in computers

  1. Data sharing - All types of buses found in a computer transfer data between the computer peripherals connected to it. The buses transfer or send data either in the serial or parallel method of data transfer. This allows for the exchange of 1, 2, 4 or even 8 bytes of data at a time. (A byte is a group of 8 bits). Buses are classified depending on how many bits they can move at the same time, which means that we have 8-bit, 16-bit, 32-bit or even 64-bit buses.
  2. Addressing - A bus has address lines, which match those of the processor. This allows data to be sent to or from specific memory locations.
  3. Power - A bus supplies power to various peripherals connected to it.
  4. Timing - The bus provides a system clock signal to synchronize the peripherals attached to it with the rest of the system.

The expansion bus facilitates the easy connection of additional components and devices on a computer such as a TV card or sound card.

Bus Terminologies

Computers have two major types of buses:

  1. System bus:- This is the bus that connects the CPU to the main memory on the motherboard. The system bus is also called the front-side bus, memory bus, local bus, or host bus.
  2. A number of I/O Buses, (I/O is an acronym for input/output), connecting various peripheral devices to the CPU. These devices connect to the system bus via a ‘bridge’ implemented in the processors' chipset. Other names for the I/O bus include “expansion bus", "external bus” or “host bus”.

Expansion Bus Types

These are some of the common expansion bus types that have been used in computers:

  • ISA - Industry Standard Architecture
  • EISA - Extended Industry Standard Architecture
  • MCA - Micro Channel Architecture
  • VESA - Video Electronics Standards Association
  • PCI - Peripheral Component Interconnect
  • PCI Express (PCI-X)
  • PCMCIA - Personal Computer Memory Card Industry Association (Also called PC bus)
  • AGP - Accelerated Graphics Port
  • SCSI - Small Computer Systems Interface

The 8 Bit and 16 Bit ISA Buses

8 Bit and 16 Bit ISA Buses

8 Bit and 16 Bit ISA Buses


This is the most common type of early expansion bus, which was designed for use in the original IBM PC. The IBM PC-XT used an 8-bit bus design. This means that the data transfers take place in 8-bit chunks (i.e., one byte at a time) across the bus. The ISA bus ran at a clock speed of 4.77 MHz.

For the 80286-based IBM PC-AT, an improved bus design, which could transfer 16-bits of data at a time, was announced. The 16-bit version of the ISA bus is sometimes known as the AT bus (AT-Advanced Technology).

The improved AT bus also provided a total of 24 address lines, which allowed 16MB of memory to be addressed. The AT bus was backward compatible with its 8-bit predecessor and allowed 8-bit cards to be used in 16-bit expansion slots.

When it first appeared, the 8-bit ISA bus ran at a speed of 4.77MHZ – the same speed as the processor. Improvements done over the years eventually made the AT bus ran at a clock speed of 8MHz.

Comparison Between 8 and 16 Bit ISA Bus

Comparison of 8-bit, & 16-bit ISA Bus as Used in Early Computers.

8-Bit ISA card (XT-Bus)16-Bit ISA (AT –Bus card)

8-bit data interface

16-bit data interface

4.77 MHZ bus

8-MHZ bus

62-pin connector

62-pin connector


36-pin AT extension connection

MCA (Micro Channel Architecture)

IBM developed this bus as a replacement for ISA when they designed the PS/2 PC in 1987.

The bus offered a number of technical improvements over the ISA bus. For instance, the MCA ran at a faster speed of 10MHz and supported either 16-bit or 32-bit data. It also supported bus mastering - a technology that placed a mini-processor on each expansion card. These mini-processors controlled much of the data transfer allowing the CPU to do other tasks.

One advantage of MCA was that the plug-in cards were software configurable; this means that they required minimal intervention by the user when configuring.

The MCA expansion bus did not support ISA cards and IBM decided to charge other manufacturers royalties for use of the technology. This made it unpopular and it is now obsolete technology.

The EISA Bus

The EISA Bus Slots (on the left) Where EISA Cards Were Connected

The EISA Bus Slots (on the left) Where EISA Cards Were Connected

EISA (Extended Industry Standard Architecture)

This is a bus technology developed by a group of manufactures as an alternative to MCA. The bus architecture was designed to use a 32-bit data path and provided 32 address lines, giving access to 4GB of memory.

Like the MCA, EISA offered a disk-based setup for the cards, but it still ran at 8MHz in order for it to be compatible with ISA.

The EISA expansion slots are twice as deep as an ISA slot. If an ISA card is placed in an EISA slot, it will use only the top row of connectors. However, a full EISA card uses both rows. It offered bus mastering.

EISA cards were relatively expensive and were normally found on high-end workstations and network servers.


It was also known as the Local bus or the VESA-Local bus. VESA (Video Electronics Standards Association) was invented to help standardize PCs video specifications, thus solving the problem of proprietary technology where different manufacturers were attempting to develop their own buses.

The VL Bus provided 32-bit data path and ran at 25 or 33 MHZ. It ran at the same clock frequency as the host CPU. But this became a problem as processor speeds increased because, the faster the peripherals are required to run, the more expensive they are to manufacture.

It was difficult to implement the VL-Bus on newer chips such as the 486s and the new Pentiums. Eventually, the VL-Bus was superseded by PCI.

VESA slots had an extra set of connectors; this made the cards larger. The VESA design was backward compatible with the older ISA cards.

Features of the VESA local bus card:-

  • 32-bit interface
  • 62/36-pin connector
  • 90+20 pin VESA local bus extension

Peripheral Component Interconnect

Peripheral Component Interconnect (PCI) is one of the latest developments in bus architecture and is the current standard for PC expansion cards. Intel developed and launched it as the expansion bus for the Pentium processor in 1993. It is a local bus like VESA, that is, it connects the CPU, memory, and peripherals to a wider, faster data pathway.

PCI supports both 32-bit and 64-bit data width; it is compatible with 486s and Pentiums. The bus data width is equal to the processor, such as a 32-bit processor would have a 32 bit PCI bus, and operates at 33MHz.

PCI was used in developing Plug and Play (PnP) and all PCI cards support PnP. This means a user can plug a new card into the computer, power it on and it will “self-identify” and “self-specify” and start working without manual configuration using jumpers.

Unlike VESA, PCI supports bus mastering. That means the bus has some processing capability and thus the CPU spends less time processing data. Most PCI cards are designed for 5v, but there are also 3v and dual-voltage cards. Keying slots used help to differentiate 3v and 5v cards and also to make sure that a 3v card is not slotted into a 5v socket and vice versa.

The PCI Slots

The PCI Bus Architecture

The PCI Bus Architecture

Accelerated Graphics Port

The need for high quality and very fast performance of video on computers led to the development of the Accelerated Graphics Port (AGP). The AGP port connects to the CPU and operates at the speed of the processor bus. This means that video information is sent more quickly to the card for processing.

The AGP uses the main PC memory to hold 3D images. In effect, this gives the AGP video card an unlimited amount of video memory. To speed up the data transfer, Intel designed the port as a direct path to the PC’s main memory.

Data transfer rate ranges from 264 Mbps to 528mbps, 800 Mbps up to 1.5 Gbps. AGP connector is identified by its brown colour.

Personal Computer Memory Card Industry Association (PC Card)

The Personal Computer Memory Card Industry Association was founded to give a standard bus for laptop computers. So it is basically used in the small computers.

Small Computer System Interface

Short for Small Computer System Interface, a parallel interface standard used by Apple Macintosh computers, PCs and Unix systems for attaching peripheral devices to a computer.

The SCSI Port

Mac LC SCSI Port

Mac LC SCSI Port

Universal Serial Bus (USB)

This is an external bus standard that supports data transfer rates of 12 Mbps. A single USB port connects up to 127 peripheral devices, such as mice, modems, and keyboards. The USB also supports hot plugging or insertion (ability to connect a device without turning the PC off) and plug and play (You connect a device and start using it without configuration).

We have two versions of USB.

USB 1x

First released in 1996, the original USB 1.0 standard offered data rates of 1.5 Mbps. The USB 1.1 standard followed with two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much less bandwidth.

USB 2x

In 2002, a newer specification USB 2.0, also called Hi-Speed USB 2.0, was introduced. It increased the data transfer rate for PC to a USB device to 480 Mbps, which is 40 times faster than the USB 1.1 specification. With the increased bandwidth, high throughput peripherals such as digital cameras, CD burners, and video equipment could now be connected with USB.

IEEE 1394

The IEEE 1394 is a very fast external serial bus interface standard that supports data transfer rates of up to 400Mbps (in 1394a) and 800Mbps (in 1394b). This makes it ideal for devices that need to transfer high levels of data in real-time, such as video devices. It was developed by Apple with the name firewire.

A single 1394 port can connect up 63 external devices.

  • It supports plug and play.
  • Supports hot plugging.
  • Provides power to peripheral devices.

The IEEE 1394 Expansion Card

Firewire Ports

Firewire Ports

Bus Architectures

Your opinion here

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: What are the characteristics of a bus?

Answer: In computers, a bus is defined as a set of physical connections that is wires or cables that are used to transmit data. They can be shared by multiple hardware components in order to communicate with one another. A computer bus is thus characterized by the amount of data or information that it can transmit at once. This amount is expressed in bits and it corresponds to the number of physical lines over which data is sent simultaneously. For instance, a 32-bit bus can transmit 32 bits in parallel.

Question: What is the address bus?

Answer: The address bus is the series of wires used to transfer data between devices that are identified by the hardware address of the physical memory (the physical address), which is stored in the form of binary numbers to enable the data bus to access memory storage.

Question: How can a single USB Port Support 127 device?

Answer: A single USB port connects up to 127 peripheral devices. This can be achieved by making use of a USB hub. The hub connects to a single USB port on your computer, but it provides multiple USB connections for your other devices. If you link a number of these USB ports, you will be able to connect the number of USB devices you want. That is how you end up with as many as 127 devices.

© 2011 Patrick Kamau


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Peter Washa Bugalama on June 10, 2020:

Good work

Wodehous.Lillian on May 06, 2020:

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Himashree barman on April 25, 2020:

Name four I/o buses in modern pc

hatoko on March 13, 2020:

what is classification of bus lines?

jackson on July 24, 2019:

thanks it was helpful but then what about the address, data and control bus. are those also types of buses. am kinda confused

Mudassir Sani on April 18, 2019:

Very Nice Thank you so much for this contribution.

Juraj from London on March 13, 2019:

Nicely and well-organized post, I need to learn from you.

Franklyn on January 15, 2019:

Thank you Mr Patrick for this page.

It was very useful and awesome....

Keep it Up Mr.Patrick

Peter Gunga on December 19, 2018:

Good notes!

Riyasudeen on August 06, 2018:


PRANEETH on July 08, 2018:

it been 6 years, that u r still commenting on this post..

Gomathi on July 05, 2018:

Thanks for very useful

josh on June 13, 2018:

nice notes

Patrick Kamau (author) from Nairobi, Kenya on May 01, 2018:

Thanks Belbo Baigans and you are much. I am happy that you were able to understand the computer bus architecture.

Belbo Baigans on May 01, 2018:

ohhh boy! its so easy to understand. stay blessed.

Marsh on April 25, 2018:

Thank you very much, if you don't mind.may u please just the books you used or I get this information

Er ashutosh21 on April 14, 2018:

Very nice....Nd very helpful.thnx.

mishy on April 03, 2018:

helped a million

Elin on March 21, 2018:

Very helpfull. Thanks man.

lilpaul on March 21, 2018:

good work. but i wish you could describe the three types of computer buses.

dalvo on February 25, 2018:

Helps alot, thanks alot

sara on January 10, 2018:


I need "fetch phase for two-bus CPU".

Can anybody help me?

I have a short time for finding that

please help me :(

Hellen Walker on December 09, 2017:

Very nicely simplified, easy to understand. Keep it up

neha on December 06, 2017:

thankx very useful

shubhanshu on November 15, 2017:


Patrick Kamau (author) from Nairobi, Kenya on November 05, 2017:

You are welcome FAIZAN ANSARI, I am happy that you can understand things clearly.

FAIZAN ANSARI on November 05, 2017:

Good article , good writing, good enough to be understood by any users at any level

Patrick Kamau (author) from Nairobi, Kenya on October 23, 2017:

You are welcome Marikoh, I am happy that you learnt something from this article.

Marikoh Ronald Owuor on October 19, 2017:

Man,this so great..it really helped me with my research.Am so much greatfull for this.

Adit mehta on October 12, 2017:

Thank-you so much

Bommanna on September 18, 2017:


Viera on July 23, 2017:

great presentation, it was very helpful to me as an A+ student...thank you so much Mr Kamau

drew jerk on July 12, 2017:

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Enaan Farhan on June 02, 2017:

Thank you very much. This article are too much informative...

sangwa gad on May 17, 2017:

thanks very more for that!!!!!

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M S Rao on May 10, 2017:

thank you very useful

Ali on March 26, 2017:

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zalwangobrie@gmail.com on March 04, 2017:

thanks for the work plus the video because its really good and educative for reseachers

Desmond Chi on February 15, 2017:

wow this was of great help to me. a big thanks to you all who through your hard work, time and patience you did a great job. more grace to you'll. it helped me to add more value in my project writing.

janny on January 16, 2017:

a lot of thank you

Vero on December 16, 2016:

Thanks Patrick Kamau for this timely piece of information. You are golden.

lk on November 23, 2016:


sylvia on November 20, 2016:

i got my assignment done..thank you

Patrick Kamau (author) from Nairobi, Kenya on August 18, 2016:

Thanks Lhoyhal for your prayers. I am glad you got what you wanted from this article.

Lhoyhal on July 09, 2016:

like wow! this piece really made sense not just to me alone, but to every other persons around that we worked together in getting our assignment done! God bless the author. Amen

TyroneK on April 28, 2016:

thanks, helped me so much in my assignment

Patrick Kamau (author) from Nairobi, Kenya on January 20, 2016:

Thanks @fidel for appreciating the work done. If you get sometime, remember to check the others.

fidel on January 20, 2016:

it was useful

Patrick Kamau (author) from Nairobi, Kenya on August 13, 2015:

You are much welcome @ gloria

gloria on August 13, 2015:

thanks,it has really helped me

Desire Murire Dtm on October 22, 2014:

its so good and reliable thanx

Patrick Kamau (author) from Nairobi, Kenya on March 12, 2014:

@dan thanks a lot.

dan on March 05, 2014:

xo helpful ...keep t up

Patrick Kamau (author) from Nairobi, Kenya on February 05, 2014:

INTEGRITY HORPEYEMI - it is simply by reading a lot and sometimes practicing what you have read.

INTEGRITY HORPEYEMI on February 05, 2014:


Patrick Kamau (author) from Nairobi, Kenya on November 07, 2013:

Thanks lucy njeri, I am glad you liked it.

lucy njeri on October 31, 2013:

good work sir.....it was of great help to me

Patrick Kamau (author) from Nairobi, Kenya on October 02, 2013:

Thanks a lot cablemanagements, for reading and commenting. I am glad you liked the article.

Patrick Kamau (author) from Nairobi, Kenya on July 16, 2013:

kudzai Muza, it is great that you have learnt something out of the tutorials that I have provided. Thanks for the comment and keep visiting. Remember to inform your friends too.

kudzai Muza on July 16, 2013:

woow now i get it !!!! thanks man!

Patrick Kamau (author) from Nairobi, Kenya on May 23, 2013:

Thanks sophie, am glad you found the article useful.

sophie on May 23, 2013:

this is so much helpful espcially for it students

Patrick Kamau (author) from Nairobi, Kenya on January 24, 2013:

Thanks madhu jayathilaka for reading and commenting. Hope you will check the other tutorials too.

madhu jayathilaka on January 24, 2013:

this is sooooooooooooooooooo gooooooooooooood

Patrick Kamau (author) from Nairobi, Kenya on January 02, 2013:

Thank you cablemanagements, for reading and commenting. I am glad you liked it.

Patrick Kamau (author) from Nairobi, Kenya on December 04, 2012:

Thanks irfan for approving this work, I am glad you liked it.

irfan on December 04, 2012:

hi this is good program

Patrick Kamau (author) from Nairobi, Kenya on November 22, 2012:

Thanks mugrewa julius for reading and commenting. If you look at the other contents I have, you can be able to get lot of other useful computer related materials. And I will keep on adding more.

mugrewa julius on November 21, 2012:

i wish you hard other subjects on computer

Patrick Kamau (author) from Nairobi, Kenya on November 21, 2012:

guitarfam, thank you for reading and commenting. I am glad you found much help from this hub. Now concerning your question, the processor relies on the timing signal which syncronizes the activities taking place in the computer.

guitarfam on November 21, 2012:

i am very impressed with this hub.this is like a textbook for me.but i have a question how does the CPU prevent two or more components from using the bus at the same time

Patrick Kamau (author) from Nairobi, Kenya on October 17, 2012:

rakesh kumar nanda, thank you too for visiting and commenting. I am glad you liked it. Wishing you all the best.

rakesh kumar nanda on October 17, 2012:

I am very pleased to learn about computer buses.It is been a great help.

I thank you again and again.

Patrick Kamau (author) from Nairobi, Kenya on September 29, 2012:

Thank you too muwonge Raphael for visiting and commenting. I am glad you like it.

muwonge Raphael on September 29, 2012:

Thanx 4 the good work done ,I appreciate it.

Patrick Kamau (author) from Nairobi, Kenya on August 17, 2012:

Azirap, I am glad you learnt something from this tutorial. Keep checking the others for more useful information. Thanks for reading and commenting.

Azirap on August 17, 2012:

It helped me in understanding the bus architecture.Not only this but it also helped me in preparing notes :)

Patrick Kamau (author) from Nairobi, Kenya on August 16, 2012:

You are welcome ndungake, I am glad you liked the tutorial. Thanks for reading and commenting.

ndungake on August 16, 2012:

thanks for this wonderful course

Patrick Kamau (author) from Nairobi, Kenya on June 20, 2012:

compufram, thanks for reading and commenting. I will surely incorporate the latest technology.

compufram on May 21, 2012:

Very interesting. I appreciate you taking the time to write such an extensive article, but I'd the new version of PCI Express, like 3.0, or USB 3.0 (SuperSpeed)made possible with the latest advances in computer processing.

Patrick Kamau (author) from Nairobi, Kenya on May 17, 2012:

reagu, thanks a lot for reading and commenting. I am glad that you found this hub useful.

reagu from Los Angeles on May 17, 2012:

This is a great resource. I built a computer last year, but prior to that, it was over 5 years ago. This hub would have helped me.

Patrick Kamau (author) from Nairobi, Kenya on May 09, 2012:

cablemanagements, thanks a lot for reading and commenting. Glad you found it useful.

S K Sinha from India on May 09, 2012:

Good article , good writing, good enough to be understood by any users at any level.

Patrick Kamau (author) from Nairobi, Kenya on April 26, 2012:

@ jeromy, thanks for reading and commenting. I will work on your request, keep checking my hubs.

jeromy on April 26, 2012:

thanks for the great work,so helpful.but i need something on logic bus.

Patrick Kamau (author) from Nairobi, Kenya on March 12, 2012:

Thanks a lot Juzzman, for reading and commenting on my work. Your compliments are accepted. All the best.

Juzzman on March 11, 2012:

ua article sooo much helpful to me.hats off for such a splendid coverage!keep it up

Favour on February 22, 2012:

I mean the typical types of board in cpu and their functions.

Patrick Kamau (author) from Nairobi, Kenya on February 11, 2012:

Thanks Ankit for reading and approving my work. If I find other relevant materials/references, I provide them inform of a link.

Patrick Kamau (author) from Nairobi, Kenya on February 11, 2012:

You are welcome ferny to read more of my work.

Patrick Kamau (author) from Nairobi, Kenya on February 11, 2012:

Thanks sachin for reading and commenting.

Ankit on February 10, 2012:

very helpful article Patkay ! thanks for posting.

do you suggest references to any other reading material which has similar info ?

ferny on February 10, 2012:

good article

sachin on February 10, 2012:


Patrick Kamau (author) from Nairobi, Kenya on February 07, 2012:

Thanks danny for reading and commenting. I am glad that my work is of great help to you.

danny on February 07, 2012:

Very Useful. I needed this lot one one page.