Industry Standard Architecture
ISA was the first motherboard slot type used on PCs, created in 1981 by IBM and updated in 1984 to 16 bits (before it was a 8-bit slot) when PC AT was released.
There is no problem installing 8-bit peripheral boards on 16-bit ISA slots. Some motherboards (as the one shown on Figure 1) have both 8-bit and 16-bit ISA slots. Very old (and huge) 8-bit ISA cards that, because of their layout, didn’t fit 16-bit ISA slots used these 8-bit ISA slots.
Usually when we refer to ISA slot we are talking about the 16-bit version. This model operated at 8 MHz and had a maximum theoretical transfer rate of 8 MB/s, which is a very low transfer rate for performance-demanding applications such as video, disk and networking.
ISA slots were used for many years specially because peripherals like sound cards, printers and scanners are very slot and didn’t need a bus faster than ISA. Applications like video, disk and networking were migrated to faster slot types, like PCI and AGP (and EISA and VLB during a short period of time), until ISA was completely gone.
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Figure 1: ISA slots.