kpmg3: RAM expansion with Beige G3 PowerMacs

I want to upgrade the RAM in my Power Macintosh Beige G3.
I have seen that RAM modules frequently bear the specification "CL 3-2-2" or "CL 2-2-2". What does it mean?
And which one should I look for my Mac?

Answer

CL stands for Cache Latency.

RAM chips are made of capacitors. Capacitors are charged with "1"s by the CPU or by the memory controller, otherwise they are normally set to "0"s by default. To keep the capacitors charged to "1"s, they need to be refreshed all of the time.
A "Capacitor" is a dynamic memory cell.
Memory cells are etched onto a silicon wafer in an array of columns (bitlines) and rows (wordlines). The intersection of a bitline and wordline constitutes the address of the memory cell.
Each address can be charged to read a "1" [or it is not charged (then reads a "0")] by circuits called "memory controllers".
These circuits perform functions such as:
* Identifying each row and column (row address select, or RAS, and column address select, or CAS)
* Keeping track of the refresh sequence (counter)
* Reading and restoring the signal from a cell (sense amplifier)
* Telling a cell whether it should take a charge or not (write enable)

A refresh sequence of 2 means that the memory controller takes 2 (two) CPU cycles to:
* CAS identifications (2 CPU cycles)+
* sense amplifier (2 CPU cycles)+
* write enable (2 CPU cycles).

The CPU has its own internal cache waiting on the controller for its response. The act of the CPU's internal cache waiting is called: Cache Latency (CL)
From which: CL 2-2-2 or CL 3-2-2

The greater the size of the CPU's Level 1 cache, the more important is that the RAM's memory controller takes fewer CPU cycles to performe its tasks.
This because the cache holds available to the CPU the "most recent" data stored on the RAM itself. Thus, the cache could "keep on hold" large amounts of such data, slowing down the CPU overall performance.

Needless to say, for those considering fitting an accelerator card to their own G3 Mac, should pay attention to the Cache Latency values their RAM memory modules bear:
the G4 processors available for upgrades, bear large Level 1 cache sizes (typically 1 MB).

For this reason, given performance is an important issue, memory modules bearing the CL 2-2-2 specifications should be preferred to others bearing lower ones (e.g.: CL 3-2-2 or CAS 3).

Costa

P.S. I apologies in advance should my English not be very "readable", as it is not my mother tounge (I am Italian).