VESA Local Bus

The VESA Local Bus (usually abbreviated to VL-Bus or VLB) is a short-lived expansion bus that was mostly used in personal computers. VESA (Video Electronics Standards Association) Local Bus worked alongside the ISA bus, acting as a high-speed conduit for memory-mapped I/O and DMA, while the ISA bus handled interrupts and port-mapped I/O.

Historical overview

In the early 1990s the I/O bandwidth of the ISA bus was becoming a critical bottleneck to PC graphics performance. The need for faster graphics was being driven by increasing adoption of graphical user interfaces in PC operating systems. While IBM's attempt at producing a successor to ISA with the Micro Channel Architecture was a technically viable option, it failed in the market due to its proprietary nature and imposition of licensing fees. The competing EISA open standard was still unable to offer enough performance improvement over ISA to provide a solution. Thus for a short time, hardware producers created proprietary implementations of local buses on their motherboards to give graphics cards direct access to the processor and system memory – and avoid the limitations of the ISA bus. However, as these manufacturer-specific solutions were not standardized, there were no provisions for providing interoperability between them. This led to the VESA consortium proposing and defining a Local Bus standard in 1992. Additionally while greater graphics card performance was a primary goal of VLB, other devices could also benefit from the VLB standard; notably many mass storage controllers were offered for VLB with increased hard disk performance.