Expansion [] slots

.. slots ..

The expansion slots, all mounted on what is called the "bus" move data from the CPU to the cards, and quite a few other signals as well. Details of the busses are given below. Slots in PC's are of the following variety: (see also the pins-out [text] file for details):

New mother boards today often feature a combination of ISA, VLB, and PCI slots. Depending on what expansion cards you already have, and what cards you will buy new, you generally have some range of options.

.. busses ..

Here is a quick overview of the various bus architectures available for the PC and some of the strengths and weaknesses of each. Some terms are described in more detail at the bottom. Some of this repeats information given above.

XT bus: used on the first PC/XT computers

Comments: Obsolete, very similar to ISA bus, many XT cards will work in ISA slots.

ISA bus: Industry Standard Architecture bus (aka. AT bus). Any XT card can be operated on an ISA bus.

Comments: ideal for low to mid bandwidth cards, though lack of enough IRQs can quickly become annoying.

MCA bus: Micro Channel Architecture bus (IBM, for the PS/2) requires cards specifically made for MCA.

Comments: Since MCA was proprietary, EISA was formed to compete with it. EISA gained much more acceptance; MCA is dead.

EISA bus: Enhanced Industry Standard Architecture bus - an industry attempt to equal the MCA, but never caught on. Most XT and ISA cards can be operated on an EISA bus.

Comments: EISA is great for high bandwidth bus mastering cards such as SCSI host adaptors, but its high cost limits its usefulness for other types of cards.

VLB: VESA Local Bus -- An extension of the ISA bus slot. Any XT or ISA card can be operated on a VESA bus.

Comments: VLB is great for video cards, but its lack of a good bus arbiter limits its usefulness for bus mastering cards and its moderate cost limits its usefulness for low to mid bandwidth cards. Since it can coexist with EISA/ISA, a combination of all three types of cards usually works best.

PCI: Peripheral Component Interconnect local bus - requires "made for" cards.

note: which means MAC started to use them. Comments: The newest of the buses, combining the speed of VLB with the advanced arbitration of EISA. Great for both video cards and bus mastering SCSI/network cards.

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