The Bottleneck

In 1992, the PC was undergoing a graphical revolution. Windows 3.1 was demanding high-resolution desktops. Doom was on the horizon. The Intel 486DX2-66 was a powerhouse CPU. But there was a problem: The ISA Bus.

The Industry Standard Architecture (ISA) bus was a relic from the 1984 IBM AT. It ran at a sleepy 8 MHz and was only 16 bits wide. It offered a maximum theoretical bandwidth of about 8 MB/s (in reality, much less). For a fast 486 CPU trying to push 256-color graphics at 640x480 or higher, the ISA bus was like drinking a milkshake through a coffee stirrer. The CPU would stall, waiting for the video card to accept the data.

The Local Bus Solution

The Video Electronics Standards Association (VESA) proposed a radical but simple solution: Take the CPU’s pins and extend them directly to a slot.

The VESA Local Bus (VLB) was born. It was easily identifiable. It looked like a standard black 16-bit ISA slot, but with a brown, high-density “tail” extension added to the end. This extension tapped directly into the 486’s memory bus.

Speed: It ran at the same speed as the CPU’s external bus (usually 33 MHz).
Width: It was a full 32-bits wide.
Bandwidth: Up to 133 MB/s.

Suddenly, video cards based on chips like the Tseng Labs ET4000/W32p or the Cirrus Logic GD5428 could fly. Windows windows snapped open instantly. Games ran smoother.

The Electrical Nightmare

However, VLB was a “hack”. It wasn’t a smart, buffered bus protocol. It was just wires connected to the CPU. This caused significant electrical engineering challenges:

Signal Degradation: The 486 CPU was not designed to drive signal lines across a motherboard and into expansion cards. Adding a VLB card increased the capacitance on the bus.
The “2-Slot” Rule: Most motherboards had 3 VLB slots, but the manual would warn you: “Only use 2 at a time.” If you populated all three (Video, IDE Controller, and… something else?), the signal noise would often crash the system.
Speed Limits: VLB worked great at 33 MHz (486DX-33, DX2-66). But when the 40 MHz and 50 MHz bus speeds appeared (AMD Am5x86, 486DX-50), VLB cards often failed. They couldn’t keep up with the timing. You had to add “Wait States” in the BIOS, which defeated the purpose of a fast bus.

Physical Monsters

VLB cards were long. Because the connector was an extension of the ISA slot, the cards had to be full-length to fit. They often bumped into CPU heatsinks or memory SIMMs. The connector itself was also notoriously stiff. The “VLB Lean” was a common phenomenon where the card would slowly work its way out of the slot due to the tension, requiring the user to open the case and shove it back in.

Extinction by Pentium

The death of VLB came with the Intel Pentium. The 486 was a 32-bit bus processor. The Pentium was a 64-bit bus processor with different timing logic. VLB was physically and electrically tied to the 486 architecture. You couldn’t easily stick a VLB slot on a Pentium board (though a few rare “bridge” boards existed).

Intel introduced PCI (Peripheral Component Interconnect). PCI was a buffered, intelligent, processor-independent bus. It ran at a fixed 33 MHz regardless of the CPU speed. It supported Plug-and-Play. By 1995, VLB was dead, remembered only as the “long brown slot” that gave the 486 its final glory days.