October 1999

TechCenter

The Basics of Random Access Memory

By Kevin Lewis

The most common question I get asked by people in the market for a new computer is "How much RAM should I get?" RAM, or random access memory, is the most common type of memory found in computers and other devices. It was named random access memory because any byte of memory can be accessed without touching the preceding bytes.

The amount of RAM a computer has is one of the factors that will allow you to speed up its response time. Over the past few years, RAM has dramatically decreased in price while, at the same time, requirements of programs and operating systems have increased. I usually suggest that no one purchase a computer today without at least 128 megabytes of RAM. The small extra cost now will save you from a lot of headaches down the road.

While there are many types of RAM on the market, the two most common are Dynamic RAM (DRAM) and Static RAM (SRAM). DRAM (pronounced DEE-ram) is what you find in most personal computers today. In many cases, when computer manufacturers or advertisements refer to RAM, they actually mean DRAM. The term "dynamic" indicates that the memory must be constantly refreshed or recharged, or it will lose the information it is storing. The refresh function actually happens thousands of times a second. DRAM is volatile; it loses what is being stored on it when the power is turned off.

The term "static" in SRAM (pronounced ESS-ram) is derived from the fact that it does not need to be refreshed, which makes SRAM faster. SRAM is also more reliable and less volatile than the more common DRAM but these added benefits also cost more.

The speed of RAM is measured by access time, which refers to the time a program or device takes to locate a single piece of information and make it available to the computer for processing. The slower and less expensive DRAM has access times of about only 60 nanoseconds. SRAM can have access times as low as 10 nanoseconds, and it also has a shorter cycle time than DRAM because it does not need to pause between accesses.

While this simple explanation of RAM may help clear up some confusion of what to look for when buying or upgrading your computer, other considerations to keep in mind when adding RAM include your computer's operating system, the maximum amount that can be installed in a particular machine, and the physical size, or PINS, of the RAM slots in your computer.