The VESA Local Bus (usually abbreviated to VL-Bus or VLB) was mostly used in personal computers. VESA Local Bus worked alongside the ISA bus; it acted as a high-speed conduit for memory-mapped I/O and DMA, while the ISA bus handled interrupts and port-mapped I/O.
A VLB slot itself was an extension of an existing ISA slot. Indeed, both VLB and ISA cards could be plugged into a VLB slot (although not at the same time.) The extended portion was usually coloured a distinctive brown. This made VLB cards quite long, reminiscent of the expansion cards from the old XT days. The addition resembled a PCI slot, and indeed VLB and PCI use the same physical connector. The length of a VLB slot led to an alternate expansion of the acronym: Very Long Bus.
Despite these problems, the VESA Local Bus was very commonplace on 486 motherboards. Probably a majority of 486-based systems had a VESA Local Bus video card, although early 486 systems never had VLB slots, as VLB debuted years after the introduction of the 486 processor.
By 1996, the Pentium (driven by Intel's Triton chipset and PCI architecture) had eliminated the 80486 market, and the VESA Local Bus with it. Many of the last 80486 motherboards made have PCI slots in addition to (or completely replacing) the VLB slots.
|Bus width||32 bits|
|Compatible with||8 bit ISA, 16 bit ISA, VLB|
|Clock||486SX-25: 25 MHz 486DX2-50: 25 MHz 486DX-33: 33 MHz486DX2-66: 33 MHz486DX4-100: 33 MHz486DX-40: 40 MHz486DX2-80: 40 MHz486DX4-120: 40 MHz486DX-50: 50 MHz (out of specification)|
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