What is ISA?
ISA stands for Industry Standard Architecture. ISA was introduced in 1981 as a type of bus used in PCs for adding expansion cards. ISA is one of the oldest forms of an expansion slot on a computers motherboard. ISA original 8-bit version.
In 1993, Intel and Microsoft introduced a new version of the ISA specification called Plug and Play ISA. Plug and Play ISA enables the operating system to configure expansion boards automatically so that users do not need to fiddle with DIP switches and jumpers.
Some issues with the ISA bus are:
- ISA is narrow and slow. ISA bus uses a lot of time for every data transfer, and it only moves 16 bits in one operation. The ISA bus cannot transfer enough bits at a time. It has a very limited bandwidth.
- ISA has no intelligence. This means that the CPU has to control the data transfer across the bus. The CPU cannot start a new assignment, until the transfer is completed. You can observe that, when your PC communicates with the floppy drive, while the rest of the PC is waiting. Quite often the whole PC seems to be sleeping. That is the result of a slow and unintelligent ISA bus.