ARCHIVED: What is VL-Bus or VESA local bus?

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VL-Bus is short for VESA local bus (VLB). VESA is an acronym that stands for the Video Electronics Standards Association. The VLB is an older local bus architecture popular on 486 computer systems in 1993 and 1994. PCI and AGP bus architectures have completely replaced the VLB.

The VLB is not a replacement for the expansion bus, but is instead an addition to it. The VLB was widely used on 486 motherboards, providing a wider bandwidth for peripheral data transfer than the traditional ISA bus. VLB products focused primarily on video cards and disk controllers, two areas that benefit from the faster local bus access. Using a VLB video card and I/O controller greatly increases system performance over an ISA-only system.

The VLB provides a high-speed data path between the CPU and peripherals (video, disk, network, etc.) running at the speed of the processor. The VLB is a 32-bit bus that supports bus mastering and runs at speeds up to 40MHz. The VLB generally provides up to three slots on the motherboard, each slot using one 32-bit connector placed adjacent to the standard ISA, EISA, PCI, or Micro Channel connector. For a short time, some 486 motherboards were produced that had both VLB and PCI slots.

Due to their length and the 32-bit connector, which adds an extra 116 pins to the 16-bit ISA card slot, VLB cards can require more pressure to seat properly than is common or recommended for any other type of expansion card. Insert with caution and be prepared to push hard to seat the card.

Advantages of the VLB

  • Faster processing (because competition with slower expansion cards is eliminated)
  • Faster access (because the VLB runs at the speed of the processor, rather than that of the main expansion bus)
  • Direct access to the processor bus, which is local to the CPU
  • Direct access to system memory at the speed of the processor itself
  • 32-bit data transfer capability
  • 128Mbps to 132Mbps maximum throughput
  • Different physical slot that prevents plugging a slower card into a fast slot

Limitations of the VLB

  • Available only for 486 processors
  • Not developed for the speed of the Pentium
  • Maximum speed of the VESA specification is 66MHz, but in reality the speed is limited to 33MHz.
  • Limited to a maximum of three cards depending on system resources
  • Poor implementation of bus mastering
  • Does not support plug-and-play

For additional information on the VLB, please see the following page:

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Last modified on 2018-01-18 12:49:55.