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Many years ago, computers were built with either electron tubes or discrete transistors, instead of with microprocessors. In those old computers, ferrite core RAM was the most common type. This was made of very tiny iron rings, with each individual ring representing one bit in RAM. Each of these rings had a bundle of either three or four wires threaded through it. Whether the ring was set to a 1 or a 0 depended on which direction the current flowed through the 1 and 0 wires. The remaining wires were there to read each ring's magnetic flux, to determine how each particular bit was set.
Needless to say, ferrite core memory isn't all that efficient, and you can't use it to achieve high memory densities. For example, a particular transistorized computer that was once used in a Navy defense system had only 48-Kilobytes worth of ferrite core memory. This memory, and the modules that made the memory work, occupied two entire refrigerator-sized door faces of that computer.
By the mid-1970s, when personal computers first started making the scene, the integrated circuit chip had been invented, which made possible the invention of memory chips. At first, these chips were quite expensive. A computer equipped with only two to four Kilobytes of RAM could cost thousands of dollars.
But, as with most other maturing technologies, manufacturing efficiencies went up and prices went down. By the late 1980s, three or four hundred dollars would buy you about one Megabyte worth of memory chips.
Today, memory is as cheap as it's ever been, with higher capacity chips and faster access speeds. And, you can now buy RAM in convenient plug-in modules, without needing to buy individual RAM chips that require a special tool to install.
For newer personal computers, the most common types of memory sticks are DDR-2 and DDR-3. (DDR stands for Double Data Rate.) There are also various speed ratings, which need to be matched to your motherboard and processor. You can run DDR-2 in dual-channel mode, and DDR-3 in either dual channel or triple-channel mode. This will further enhance memory performance.
You can buy either DDR-2 or DDR-3 memory in modules of up to four Gigabytes. Pricing will depend on quality, capacity, and speed-rating. Most modern computers allow you to insert at least four modules.
If you search on the web, you'll be able to find plenty of computer memory vendors. Some of these vendors have downloadable utilities that will tell you exactly what type of memory modules you'll need to upgrade your Windows or Mac computer. (The Mac versions support both Intel and PowerPC architectures.)
Most of these utilities don't support alternate operating systems, such as Linux. But, the vendors' websites will allow you to manually select the brand and model of your computer, so that you'll still be able to find the kind of memory that your machine requires.
If you're in the market for computer memory, a quick web search should help you to find it.
