Front Side Bus

The Front Side Bus (FSB) is the connecting path between the CPU and other key components such as system memory.

The Front Side Bus is also called the Data Bus and the Processor Side Bus (PSB).

Front Side Bus Widths of Various CPUs

CPU	Front Side Bus Width
8088	8
8086	16
80286	16
80386SX	16
80386DX	32
80486	32
AMD 5×86	32
Pentium	64
AMD K6	64
Pentium Pro	64
Celeron	64
Pentium II	64
Pentium III	64
AMD Duron	64
AMD Athlon	64
AMD Athlon XP	64
Pentium 4	64
Itanium	64
AMD Athlon 64	64

Competing Front Side Bus Technologies

The EV6 Front Side Bus

AMD uses the EV6 Front Side Bus in its Athlon and Athlon XP CPUs.

Athlon and Athlon XP CPUs with the EV6 bus are able to transfer data over the Front Side Bus twice per processor cycle.

The AGTL+ Front Side Bus

Intel uses the AGTL+ Front Side Bus in its Pentium 4 processors.

Pentium 4s with AGTL+ are able to transfer data over the Front Side Bus four times per processor cycle.

However, the AGTL+ bus is shared among all of the systems CPUs. The EV6 bus is a point-to-point bus, meaning that the full bandwidth of the bus is available to every CPU.

HyperTransport

AMD Athlon64, AthlonFX, and Opteron CPUs utilize the HyperTransport Bus.

These CPUs move the memory controller into the CPU, effectively eliminating the Front Side Bus.