(ISA) This is a (very loose) set of rules by which your PC expansion slots and expansion cards operate. Newer Pentium type computers (and newer Macs) now contain PCI slots in preference to the older 8-bit or 16-bit ISA slots. PCI slots can handle a much higher data transfer rate and are preferred, however for most musical applications ISA slots do the job adequately for MIDI interfaces and MIDI and audio soundcards.