dependent on the cards and CPU. This simplicity of VLB unfortunately created several factors that served to limit its useful life substantially: 80486 dependence The VESA Local Bus relies heavily on the Intel 80486 CPU's memory bus design. When the Pentium processor arrived, there were major differences in its bus design, not easily adaptable to a VESA Local Bus implementation. Few Pentium motherboards with VLB slots were ever made and use VLB-to-PCI bridges such as the OPTi 82C822. This also meant that moving the bus to a computer with a non-x86 architecture was nearly impossible, within practical economic constraints. Limited number of slots available Most PCs that use VESA Local Bus have only one or two VLB-capable ISA slots out of the total five or six available; thus, four ISA slots generally are just that, ISA-only. This is a result of VESA Local Bus being a direct branch of the 80486 memory bus. The processor does not have sufficient electrical capacity to correctly drive (signal and power) more than two or three devices at a time directly from this bus. Reliability problems The strict electrical limitations on the bus also reduce any safety margin available, negatively influencing reliability. Glitches between cards are common, as the interaction between individual cards, combinations of cards, motherboard implementation, and even the processor itself are difficult to predict. This is especially prevalent on lower-end motherboards, as the addition of more VLB cards could overwhelm an already marginal implementation. Results can be rather spectacular when often important devices such as hard disk controllers are involved with a bus conflict with a memory-intensive device such as the ubiquitous video card.As VLB devices have direct high-speed access to system memory at the same level as the main processor, there is no way for the system to intervene if devices were mis-configured or became unstable. If two devices overwrite the same memory location in a conflict, and the hard-disk controller relies on this location (the HDD controller often being the second conflicting device), there is the all-too-common possibility of massive data corruption. Limited scalability As bus speeds of 486 systems increased, VLB stability became increasingly difficult to manage. The tightly coupled local bus design that gives VLB its speed became increasingly intolerant of timing variations, notably past 40 MHz. Intel's original 50 MHz 486 processor faced difficulty in the market, as many existing motherboards (even non-VLB designs) did not