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Bus
A bus is a group of parallel communication lines used to connect multiple functions or components of a computer.
Among other things, a bus is used to transmit data and control signals for various functions, supply power, etc.
Once more experience had been gained, designers began systematising computers further and dividing them into different functional blocks. Gradually, the connections between these elements were no longer made using unmanageable cabling and wires.
Instead, the different system components were connected to one another using bus systems.
Today, for example, one refers to an internal CPU bus or a bus between the individual motherboard components of a PC (over which the data transfer between the CPU, memory and other components takes place), etc.
Ports for connecting peripheral devices are also called buses if they are able to connect a number of devices. The expansion bus also plays a very important role.
A bus is usually subdivided into a data, address and control bus.
With the first IBM PC, a PC bus system was introduced that had a total of 62 lines, including 8 data and 20 address lines. An expansion card with 62 contacts could be inserted into the PC bus connectors – usually referred to simply as "the bus".
With the IBM PC/AT, the bus was expanded by an additional 36 lines, including, among others, 8 data lines. The connectors on this ISA bus were designed so that the old 8-bit cards could be used as well as the new 16-bit cards introduced at the time. The ISA or AT bus is still used in today's AT class computers.
IBM's introduction of a new bus system, known as the MicroChannel, with 32 data lines in the IBM-PS/2 as well as the renewed expansion of the ISA bus by an additional 16 data lines to form the EISA bus achieved importance in high end applications only.
Once the 32-bit VESA local bus had made a brief debut in PC graphics in particular, the 32-bit-wide PCI bus is also taking on an important role in PCs.
The most important buses are: AGP, IDE and SCSI.
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