Cache On A STick
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.
(01 Feb 1996)
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