RAM Demystified

by Ryan, ryan@smalldog.com

RAM, sometimes simply called memory, acts as a buffer between your computer’s CPU (processor) and its hard drive to speed up access to files and programs in use. RAM is much faster in its overall throughput (the speed data can be transfered) and latency (time to respond to requests for data).

Whenever you start a program on your computer, some or all of it is loaded into memory. You will experience extreme slowdown and the spinning beach ball if you do not have enough memory installed. In this case your computer will be accessing the hard drive directly, as if it were very very very slow ram, slowing your entire computer down to match the speed of the drive. OS X Tiger 10.4 does not operate very well with 256MB of ram and 512MB is the absolute minimum. For an optimal experience, I recommend at least 1GB of RAM, but more will make most every function smoother and faster.

The other type of memory in your computer is some of the same sort, but the difference is that it is much faster and it is directly
plugged into the CPU allowing for near instantaneous data retrieval.

This ram is called L2 Cache and comes in small amounts of about 2MB and 4MB. Your computer uses an algorithm to try to predict what data it will need next and will load it out of your RAM and into your L2 Cache.

The memory in the current line of Macs runs at 667MHZ (667 million cycles per second), a huge increase over the last generation of Macs whose memory ran at 333MHZ. The full Apple computer lineup also include dual channel technology, which works when memory chips are installed in pairs. The theoretical speed increase by installing in pairs is 100%, but real-world testing indicates differences ranging from barely perceptible to life-altering. This is because memory fires in bursts and by offsetting the burst of one chip it can theoretically send twice as much data through the memory bus in the same amount of time. A rough analog is the opening of a second
checkout line at a supermarket.

The Mac Pro is special, though: if you install identical chips four
at a time, you can take advantage of the 256-bit wide memory
architecture.

by Ryan, ryan@smalldog.com