Cache On A STick

architecture (COAST) Intel Corporation attempt to's

standardise the modular L2 cache subsystem in

Pentium-based computers.

A COAST module should be about 4.35" wide by 1.14" high.

According to earlier specifications from Motorola, a module

between 4.33" and 4.36" wide, and between 1.12" and 1.16" high

is within the COAST standard. Some module vendors, including

some major motherboard suppliers, greatly violate the height

specification.

Another COAST specification violated by many suppliers

concerns clock distribution in synchronous modules. The

specification requires that the clock tree to each synchronous

chip be balanced, i.e. equal length from edge of the connector

to individual chips. An unbalanced clock tree increases

reflections and noise.

For a 256 kilobyte cache module the standard requires the

same clock be used for both chips but some vendors use

separate clocks to reduce loading on the clock driver and

hence increase the clock speed. However, this creates

unbalanced loading in other motherboard configurations, such

as motherboards with soldered caches in the system.

(1996-06-10)