ABC of ICT

28th April 2006 at 01:00
Pete Roythorne gets to grips with his computer's memory

If you have ever looked at the specifications of a new computer you've probably been left wondering what a 2.8GHz processor, 512Mb Ram, a 1Mb cache and a 200Gb hard drive means. The answer is, it's all about memory.

Memory refers to fast, temporary forms of electronic storage in your computer. If your computer's processor (the brains, if you like, of the machine) had to constantly look to the hard drive to access data, very little would ever get done, as it would be too slow. When the information is held in memory, the processor can access it much more quickly.

Every time you open a piece of software or a file within that software, it is put in the computer's temporary storage areas so the processor can access that information more easily.

A typical computer would have the following types of storage areas: level 1 and level 2 caches, system Ram (random access memory), virtual memory and a hard disk. Modern, high-speed processors need fast access to huge amounts of data. If they can't get it, they stop and wait for it. Unfortunately, the memory that can keep pace with this is extremely expensive. So memory is designed in a tier system - using expensive memory in small quantities and backing it up with larger quantities of the less expensive variety.

The cheapest form of memory is the computer's hard disk, providing large quantities of permanent storage. This forms the computer's virtual memory.

The next level in the hierarchy is Ram. Its speed is controlled by "bus width" (this refers to the number of bits of information that can be sent to the processor simultaneously) and "bus speed" (the number of times a group of data can be sent each second). However, even with a wide and fast bus, it still takes longer for data to get from the Ram to the processor than it takes the processor to actually process the data.

To alleviate this bottleneck there is a cache, which makes the most frequently used data instantly available to the processor. This is achieved by building a small amount of memory (primary or level 1 cache) into the processor. Any secondary or level 2 cache is normally on a memory card close to the processor, with a direct connection to it. Some cheaper systems dispense with level 2 cache altogether, and many high-end processors now have it built in.

In short, if you think about your computer as a team, with all the main components - the central processing unit, the hard drive and the operating system - working together, then memory is one of the most essential parts of how the team functions.

* In the column on control software (March 10) the link for Logo software is www.logo.com or www.logotron.co.uk and not as listed

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