Dear Julie,
first of all, welcome to Apple Discussion Forums. I sincerely hope you will like it here, as much as we do.
Upgrading the RAM in any computer (including PeeCees) is, perhaps, one of the most "intimate" upgrades you could do to it, second only to upgrading the CPU.
The majority of data processing inside a modern computer, "happens" between the RAM banks and the CPU, through the Front System Bus; data flows are managed by a chip soldered on the mother board, called MEMORY CONTROLLER (herein after called just "MC").
Among other things, the MC detrmines:
- The clock frequency to run the Front System Bus at any given moment (or task). Computer specs only tell you the maximum frequency the bus can run at, but the MC, as it manages the clock running the bus, can choose different frequencies depending on the tasks it has at hand, up to such maximum frequency.
- The minimum SDRAM module specifications which it "needs" to address during the various data flows; in particular, the minimum TIMING specs such modules need to be capable of.
The MC fitted inside the PowerMac G4 Cube machine in particular (technically known as the UNI-North IC Bridge), needs the following minimum SDRAM frequency and timing specs:
- PC-100 compliant modules - It means that the modules must be stated to run safely at frequencies up to 100MHz minimum.
- Capable to sustain a refresh sequence of 8 nano seconds - It means that, when and if needed, the module can performe a refresh sequence at 125MHz.
See these
Apple Developer Notes for more details, if you are curious.
Today you will find it hard to find 168-pins, 3.3 volt standard SDRAM modules rated at "just" 100MHz (PC-100). Most vendors out there will offer you PC-133 rated modules, as the PC-100 specification is a very old one in computer terms and hardly (if no longer) used by modern computers.
However, most PC-133 rated SDRAM modules are backward compatible to the PC-100 standard and can easely sustain refresh sequences of 8 ns. As a matter of fact, PC-133 modules should all be capable of refresh sequences as down as 7.5 ns.
The important thing is that the vendor is capable to provide you with SDRAM modules tested ALSO at 100MHz frequency.
Another important spec you should be aware of, is the SDRAM module data density it is built with: modules bearing DRAM devices with data densities over 256Mbits (NOT to be confused with Mega Bytes), will only be "seen" by your system as half (or less) the nominal capacity of the module.
This because your MC is NOT capable to address more than 256 Mega bits of data per memory page. Thus, if you are looking to fit inside your Cube 1.5GB of RAM, you will need 3 SDRAM 512MB modules.
Each module should then have 16 DRAM devices soldered on it: 8 on each side of it [As: (256 / 8 = 32) and (32 x 16 = 512)].
Macs and OS X in particular, are both very demanding as reguards to RAM specifications and you can easely have an unstable system if the wrong and/or poor quality kind of RAM modules are fitted inside it.
That is why I tend to reccomend users to buy their expansion RAM modules from trusted and known suppliers.
I personally buy all my memory expansions from either
Crucial Technology or from
MacGurus.
Both suppliers throughly test their products prior to selling them and provide excellent after sale service.
All the best.
Ciao.
Costa
