FRONTSIDE BUS

5/13/2000

Frontside Bus: Part of a system called Dual Independent Bus (DIB) that was devised with the advent of fast, tightly coupled, off-chip caches in the Pentium Pro CPU. The Frontside Bus is the part of the DIB that talks to main memory, to the chipset, and to peripherals. The faster backside bus communicates with the L2 cache.

The dual buses provide fully independent paths to the CPU and to the internal L1 cache. This architecture allows the L2 cache to be read and written without blocking the main memory bus and vice versa. This is important because without the dual bus structure, access to the L2 cache would be blocked frequently while the CPU waits for relatively slow operations on the Frontside Bus.

The backside bus will typically operate at a submultiple (1x, 1/2x, 1/3x, etc) of the CPU frequency. The frontside bus typically operates at a multiple (1x, 2x, 3x) of the PCI bus frequency.

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