Editing VESA Local Bus (section)

==Historical overview==
[[File:KL ATI Mach 64 VLB.jpg|thumb|left|upright=1.5|An ATI MACH64 [[Super VGA|SVGA]] VLB graphics card]]

In the early 1990s, the [[I/O]] bandwidth of the prevailing ISA bus, 8.33 MB/s for standard 16 bit 8.33&nbsp;MHz slots, had become a critical bottleneck to PC video and graphics performance. The need for faster graphics was driven by increased adoption of [[graphical user interface]]s in PC operating systems. While IBM did produce a viable successor to ISA with the [[Micro Channel Architecture]] offering a bandwidth of 66 MB/s, it failed in the market because hardware manufacturers did not want to pay steep licensing fees to use it. While an extension of the royalty-free ISA bus in the form of [[Extended Industry Standard Architecture|EISA]] open standard was developed to counter MCA, its bandwidth of 33.32 MB/s was unable to offer enough improvement over ISA to meet the significant increase in bandwidth desired for graphics. It would be superseded by [[Peripheral Component Interconnect]] (PCI), starting at speeds of 133 MB/s (32-bit at 33 MHz in the standard configuration)

Thus for a short time, a market opening occurred where video card manufacturers and motherboard chipset makers created their own proprietary implementations of [[local bus]]es to provide graphics cards direct access to the processor and system memory. This avoided the limitations of the ISA bus while being less costly than a "licensed IBM MCA machine". At the time, the cost to migrate to an MCA architecture machine from an ISA machine was substantial. MCA machines generally did not offer ISA slots, thus a migration to MCA architecture meant that any prior investment in ISA cards was made unusable. Additionally, makers of MCA-compatible cards were subject to IBM's licensing fees, which combined with MCA's greater technical requirements and expense to implement. It did have the effect of making an MCA version of a peripheral card significantly more expensive than its ISA counterpart.

So while these ad-hoc manufacturer-specific solutions were effective, they were not standardized, and there were no provisions for providing interoperability. This drew the attention of the [[VESA]] consortium and resulted in a proposal for a voluntary and royalty-free local bus standard in 1992.<ref>Richter, Jake. [https://books.google.com/books?id=XlEEAAAAMBAJ&pg=PA66 "Local-bus architecture: A little-understood, much-cited graphics technology"], ''InfoWorld'', May 18, 1992, accessed March 9, 2011.</ref> An additional benefit from this standardization (beyond the primary goal of greater graphics card performance) was that other devices could also be designed to utilize the performance offered from VLB; notably, mass-storage controllers were offered for VLB, providing increased hard-disk performance. VLB bandwidth depended on the CPU's bus speed: It started at 100 MB/s for CPUs with a 25&nbsp;MHz bus, increased to 133 MB/s at 33&nbsp;MHz and 160 MB/s at 40&nbsp;MHz, and reached 200 MB/s at 50&nbsp;MHz.