This should give you a clearer idea on the distinction of RAM and the hard disk drive. Now, recall back from the guide on Processors the idea of “Virtual memory.” Virtual memory, or swap space, is simply space on the hard drive that is swapped between RAM and the hard drive. Thus, it allows more memory to be available to local memory, but at a slower speed (the speed of the hard drive interface, more specifically).

ROM

Now, RAM and ROM are similar acronyms, but perform completely different functions. RAM is as described above, while ROM, Read Only Memory, is memory that is retained even after an electrical charge is lost (unlike RAM). A good, well recognizable example of ROM is found in virtually every PC made – the CMOS/BIOS chip.

Required Reading

Now, for more information concerning the types and makes of ROM and RAM, I would advise you to check out PC Mechanic’s guide to memory types, found at http://www.pcmech.com/show/memory/110/. Note that the knowledge found within this article is essential to doing well on the A+ exam. Later in this guide you will find a few questions that assume you have read the provided linked material, so read up carefully!

Exploring Parity

One of the earliest considerations in the design of memory concerned the ability of the PC to “check” the memory; that is, for the PC to assure it can retain data properly. A simple method was developed to do just this, and it is known as “parity checking.” Now, one might be wondering at this point what parity is in the first place. Parity is the state of a given byte of data being either even or odd. Imagine exactly how parity could be employed in the checking of memory. You should have imagined something along the following lines: the computer assigns each memory byte a number, even or odd, based on a known sequence. The memory byte is then compared in parity with the computer’s predicted result, and if the two match, the byte is said to be good. Now, this is very simplistic in comparison to the real parity process, but it is all that is necessary to understand in order to grasp the concept of parity.

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