---
tags:
  - Electronics
  - Hardware
---

# Bus
A bus is a communication system that transfers data between components inside a computer, or between computers.  

## Main buses 

### System bus
The primary pathway between the CPU and [memory](Memory/Basics.md).

### Internal bus
Connects local devices for example the harddisk to the CPU.

### External bus
Connects peripheral devices such as disks and printers to the [motherboard](Motherboard.md)

### Expansion bus
Allows expansion boards to access the CPU and memory. 

### Frontside bus
Main computer bus that determines data transfer rate speed and is the primary data transfer path between the CPU, RAM and other [motherboard](Motherboard.md) devices.

### Backside bus
Transfers secondary cache (L2 cache) data at faster speeds, allowing more efficient CPU operations

## Bus standards

### Parallel and serial transmission types
There is a distinction between buses that use serial and buses that use parallel transmission. They are distinguished by the way in which data in the form of bits is transferred from one point to another, along the bus.

Serial Transmission is the type of transmission in which a single communication link is used to transfer the data from an end to another. On other hand Parallel Transmission is the transmission in which multiple parallel links are used that transmit each bit of data simultaneously.

<img src="../img/serial-transmission.jpg" width="800px"/>
<img src="../img/parallel-transmission.jpg" width="800px"/>

* Serial buses are cheaper to implement than parallel buses
* Serial buses are slower than parallel buses

## Standards
The mode of transmission is used to distinguish the different bus standards.

SCSI (Small Computer System Interface) and ATA (Advanced Technology Attachment) are used for hard drive devices (i.e. internal buses). USB (Univeral Serial Bus) and SATA (Serial Advanced Technology Attachment) are used for peripheral devices, keyboards and modem devices (i.e external buses).