The VESA Local Bus, also called VL-Bus or more commonly VLB, was the first local bus used on PCs. Introduced in 1992, VLB video became very popular during the heyday of the 486, in particular 1993 to 1994. VLB cards can be easily identified by their longer connectors, compared to standard ISA card slots. See here for details on the VESA local bus.

VLB video cards provide, in general, much better performance than ISA cards. This is primarily due to the fact that the 32-bit local bus used by VLB cards allows for several times more data throughput between the card and the processor than ISA allows. VLB has however had its own share of problems. In particular, VLB video cards may cause reliability problems in motherboards running at 40 or 50 MHz.

Many VLB cards are very good performers, but are hampered by their general age, along with that of the motherboards they run in; most are at least four years old and new development of better and faster chipsets is entirely in the PCI world now. Still, despite the fact that VLB is older than PCI, it can provide quite acceptable performance (although probably fewer features and less video memory). VLB is much closer to PCI than it is to ISA. Any system that will support VLB should be using it for the video card; the performance improvement over ISA is substantial in most cases.

Note: VESA Local Bus video is generally limited to 486 PCs (or other motherboards that use a fourth-generation processor). The vast majority of Pentiums and later PCs use PCI (or AGP) and do not support VLB at all, although there are some very old Pentium systems that are VLB-based.

This is an archive of Charles M. Kozierok’s PCGuide (pcguide.com) which disappeared from the internet in 2018. We wanted to preserve Charles M. Kozierok’s knowledge about computers and are permanently hosting a selection of important pages from PCGuide.

VESA Local Bus (VLB)

The first local bus to gain popularity, the VESA local bus (also called VL-Bus or VLB for short) was introduced in 1992. VESA stands for the Video Electronics Standards Association, a standards group that was formed in the late eighties to address video-related issues in personal computers. Indeed, the major reason for the development of VLB was to improve video performance in PCs.

The VLB is a 32-bit bus which is in a way a direct extension of the 486 processor/memory bus. A VLB slot is a 16-bit ISA slot with third and fourth slot connectors added on the end. The VLB normally runs at 33 MHz, although higher speeds are possible on some systems. Since it is an extension of the ISA bus, an ISA card can be used in a VLB slot, although it makes sense to use the regular ISA slots first and leave the (small number of) VLB slots open for VLB cards, which won’t work in an ISA slot of course. Use of a VLB video card and I/O controller greatly increases system performance over an ISA-only system.

While VLB was extremely popular during the reign of the 486, with the introduction of the Pentium and its PCI local bus in 1994, wholesale abandonment of the VLB began in earnest. While Intel pushing PCI was one reason why this happened, there were also several key problems with the VLB implementation. First, the design was strongly based on the 486 processor, and adapting it to the Pentium caused a host of compatibility and other problems. Second, the bus itself was tricky electrically; for example, the number of cards that could be used on the bus was low (often only two or even one), and occasionally there could be timing problems on the bus when more than one card was used. Finally, the bus did not support bus mastering properly since there was no good arbitration scheme, and did not support Plug and Play.

Today VLB is obsolete for new systems; even the latest 486 motherboards use PCI, and all Pentiums and higher use PCI. However, these systems do still offer reasonable performance, and are now plentiful and very inexpensive–if you can still find them.

This is an archive of Charles M. Kozierok’s PCGuide (pcguide.com) which disappeared from the internet in 2018. We wanted to preserve Charles M. Kozierok’s knowledge about computers and are permanently hosting a selection of important pages from PCGuide.