A bus is a set of signal pathways that allow information to travel between components inside or outside of a computer.

Types of Bus

External bus or Expansion bus allows the CPU to talk to the other devices in the computer and vice versa. It is called that because it's external to the CPU.

Address bus allows the CPU to talk to a device. It will select the particular memory address that the device is using and use the address bus to write to that particular address.

Data bus allows the device to send information back to the CPU


Types of Expansion Buses

Introduced by IBM, ISA or Industry Standard Architecture was originally an 8-bit bus and later expanded to a 16-bit bus in 1984. When this bus was originally released it was a proprietary bus, which allowed only IBM to create peripherals and the actual interface. Later however in the early 1980's the bus was being created by other clone manufacturers.

This is still in use because it's cheap and for backwards compatibility

isa card16bit ISA Card

isa slot16bit ISA Slot

Introduced by Intel in 1992, PCI is short for Peripheral Component Interconnect and is a 32-bit or 64-bit expansion bus.
The PCI bus is the most popular expansion bus use in today's computers

pci cardPCI Card

pciPCI 64 and 32bit Slot

Introduced by Intel in 1997, AGP or Advanced Graphic Port is a 32-bit bus or 64-bit bus designed for the high demands of 3-D graphics. AGP has a direct line to the computers memory which allows 3-D elements to be stored in the system memory instead of the video memory.
AGP is one of the fastest expansion bus in use but its only for video or graphics environment.

agp cardAGP Card

agp slot AGP Slot

Expansion Bus Chart:

Type of Bus Bits Wide Clock Speed Transfer Speed
ISA 8 bit 4.77 MHz 2.38MB/s
ISA 16 bit 8.33 MHz 8MB/s
PCI (Client) 32 bit 33MHz 133MB/s
PCI (Server) 64 bit 66MHz 266MB/s
AGP 1x 32 bit 66MHz 266MB/s
AGP 2x 32 bit 66MHz 533MB/s
AGP 4x 32 bit 66MHz 1,066MB/s
AGP 8x 32 bit 66MHz 2,133MB/s
AGP 8x (high-end) 64 bit 66MHz 4,266MB/s

Bus Mastering-Ability of bus device to bypass the CPU can be set at the CMOS setup

Other Buses


USB or Universal Serial Bus is an external bus that most popular form of bus use today

USB is hot swappable

USB can daisy chain up to 127 devices

USB Speeds

USB 1.0 supports 1.5Mbps
USB 1.1 supports 12Mbps
USB 2.0 supports up to 480Mbps
USB 3.0 supports up to 4.8Gbps
USB 3.1 supports upt to 10Gbps

usb_a USB_A Connector

usb_b USB_B Connector

USB_C Connector

Firewire (IEEE 1394)

Firewire is use to connect high speed devices

Firewire is hot swappable

Firewire can daisy chain up to 63 devices

Firewire Speeds

Firewire A supports 400Mbps
Firewire B supports 800Mbps
Firewire 1600 supports up to 1600Mbps
USB 3200 supports up to 3200Mbps

4pin firewire port 4pin

9pin 9pin

6 ping 6pin


Thunderbolt Port

Thunderbolt Speeds

Thunderbolt 1 10 Gbps
Thunderbolt 2 20 Gbps
Thunderbolt 3 40 Gbps
Thunderbolt 4 40 Gbps

Released September 8, 1998, AMR is short for Audio/Modem Riser. AMR allows an OEM to create one card that has the functionality of either Modem or Audio or both Audio and Modem on one card. This new specification allows for the motherboard to be manufactured at a lower cost and free up industry standard expansion slots in the system for other additional plug-in peripherals.

amr slot AMR Slot


Introduced by Intel February 7, 2000, CNR is short for Communication and Network Riser and is a specification that supports audio,modem USB and Local Area Networking interfaces of core logic chipsets.

cnr slot CNR Slot

PCI-X is a high performance bus that is designed to meet the increased I/O demands of technologies such as Fibre Channel, Gigabit Ethernet and Ultra3 SCSI.

pci-x cardPCI-X card

 PCI-X Slots

Type of Bus Bits Wide Clock Speed Transfer Speed
PCI-X (v1) 64bit 66MHz * 8 = 528MB/s
PCI-X (v1) 64bit 100MHz * 8 = 800MB/s
PCI-X (v1) 64bit 133MHz * 8 = 1066MB/s

PCI Express A high speed serial I/O interconnect standard being used for high speed connection it will eventually replace the PCI standards

PCI-e Card


Lane Widths Peak unidirectional bandwidth Peak full duplex bandwidth
x1 250MB/s 500MB/s
x2 500MB/s 1GB/s
x4 1GB/s 2GB/s
x8 2GB/s 4GB/s
x16 4GB/s 8GB/s

pciePCIe slots

Laptop Buses

Personal Computer memory card international association is a type of bus use for laptops. There are different types of cards and you primarily slide in the card in a PC card slot of a laptop.

pcmcia cardType II PCMCIA Card

PC Card Types Measurement Usage
Type I 3.3mm Flash Memory
Type II 5.0mm USB/NIC/Wireless
Type III 10.5mm Hard Drive

PCMCIA cards supports 16 or 32 bit bus width

Express Card is the newest form of card you insert in newer laptops

Special Thanks to How Stuff works, Belkin, nVidia, Linksys, ATI and Intel