In this article we're going to review the different types of computer memory as they do not all function the same way.
The most common and most often used computer memory is your RAM which stands for Random Access Memory. Random Access Memory is considered random access because you can access any cell of the memory at any time for any piece of information either for retrieval or storage if you know the row and column that intersect at that cell. For example: let's say we are working within an Excel spreadsheet and we want to change the value in cell A1 from 100 to 90. In order to do this the computer has to know where on the RAM chip that cell's contents are located. Fortunately for the user, it does and the user doesn't have to. Once the change is made the computer replaces the contents in RAM, which was the value 100, with the new value of 90 and leaves it in that location until the user decides to change the value again or closes up the spreadsheet itself. Once that happens, the contents in RAM of that particular location are lost. Hopefully before doing this the user will have saved his spreadsheet to his computer's hard drive.
RAM can also be broken down into different types. First there is SRAM, which is Static Random Access Memory. This type of memory is usually used for a computer's cache memory. Then there is DRAM, which is Dynamic Random Access Memory. This type of memory has memory cells with a paired transistor and capacitor which need constant refreshing. Then there is EDO DRAM which is Extended Data Out Dynamic Random Access Memory. This is very fast memory which doesn't wait until processing of the first bit is completed before moving on to the next bit. Then we have SDRAM, which is Synchronous Dynamic Random Access Memory. This type of memory takes advantage of the fact that in most cases the data that needs to be accessed is sequentially stored and therefore using a very fast method of accessing this memory. The rate of this memory is about 528 Mbps, which is extremely fast.
The opposite of RAM is SAM, or Sequential Access Memory. This is memory that has to be accessed in sequence, one cell at a time until the location the user is looking for is found. This memory is very good for buffer memory because items stored in the buffer are usually stored sequentially anyway as the user continues his work. SAM is slower than RAM as far as access time goes.
Another type of memory is what is known as ROM or Read Only Memory. Read Only Memory is also known as Firmware. This is an integrated circuit programmed with certain data when it is manufactured. ROM is not only used in computers but in a number of electronic devices like your Xbox or any video game console box. Without ROM just about any electronic item today that has built in functions simply wouldn't work.
There are many other different types of memory but these are the most common. In future articles we'll go more deeply into how memory in your computer and other devices works.
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Michael Russell
Your Independent guide to Computer Memory
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