VLB MASTERING

5/11/97

Vesa Local Bus (VLB) Mastering: The VESA Local Bus is a technology widely used on 486 computers. VLB cards are easily recognized by an additional set of 120 (60 per side) connections behind the normal 16 bit ISA connections. VLB cards will allow speeds to 33MHz. It has been reported that VLB cards may not be able run at their highest speed when more than one card is used in a machine. As a practical matter VLB was generally used almost entirely for Video and Multi-I/O cards. VLB has been replaced by PCI although a few early Pentiums had VLB slots.

Many VLB form factor slots will support 33MHz VLB cards but do not support bus mastering. These are commonly referred to as "Slave" slots although they are not "slaves" in the common sense of having some signals controlled by a separate master. They are more accurately described as non-VLB compliant slots since they do not comply with the VESA specification. Most (maybe all) VLB video cards do not perform bus mastering, and will run perfectly in a "slave slot".

When setting up a VLB computer, care should be taken to put bus mastering cards into "master" slots. Non-bus mastering cards ("slaves") may be used in any slot as may ordinary ISA cards.

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