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          This is a key concept in the understanding of the operation of a computer. RAM is an acronym for Random Access Memory which means one can get straight access to any place of that memory to read and write information. It is also simply called memory. When one talks about "memory" the beginner tends to think about hard disks, data stored in mass storage devices (peripherals) whereas the computerman knows one is talking about RAM which is not the same thing at all.

          What is that memory, RAM?

          It designates the component that you can see on this picture of a memory board


and in other contexts it means the amount of memory held in that component. This component contains astronomical amounts of condensers and transistors which work per the explanation given above about them.

          A chief difference with mass storage devices is that the access time to this type of memory is about 200 times faster. This RAM is located very close to the processor and serves as fast memory to store active programs as well as intermediate data and results which the processor may need.

          Suppose you dubble-click on an icon to launch a program. The computer will first fetch on your hard disk the file or files related with that program and copy them into the RAM. One says the program is "loaded" or "loaded in memory". Now the processor is going to read that memory and carry out instructions of the program one by one. And it will keep that program in memory till at least the end of its execution. If there is enough available memory it will even keep it longer so that when you have to call that program back it takes less time. Should there be a memory shortage (because many processes are running) the processor would free the memory space occupied by that program to make it available for other programs to run. To illustrate this you may notice that the first time you call the search engine for this site it (unfortunately) takes some time for it to load in memory. But at later calls it's much faster. The reason is that it was kept in memory. Of course at each restart of the computer it must be reloaded in memory at its first use.

          You might ask then why not replace all hard disks by that type of memory. Because on one side RAM is more expensive also the architecture is such that it would probably be difficult to preserve the speed of access with larger quantities of it and last but not least because that memory is not persistent. When you turn your computer off that memory get emptied out. Everything goes automatically to 0 because all the condensers get discharged then.

          So all informations are recorded on hard disks where they can remain for years. But every time a program is called its related files are loaded in memory (if they aren't already in there) and the processor can work with them.

          How much RAM does one need? Nowadays 32 MB (megabytes) seem to be an acceptable minimum. It all depends on what type of machine you got and the number of programs which are memory hungry. Video games are very hungry of it. 64 MB will be more comfortable, 128 would be a good amount and 256 or 512 even better.

Virtual memory

          What happens when there is not enough memory? This can happen if you carry out too many programs at the same time. Let's say you open several windows, text treatment, you run your mail program and launch a DVD and all these programs try to get loaded into memory until there is no more of it... At that point the processor will use a part of your hard disk. This is called swapping. However the access time is far slower and further the processor now has to manage the distribution of memory for all these programs. Some parts are in the RAM, others are in the swap. One has to keep track of all that and this in itself adds to the consumption of resources of the processor. That part of the hard disk being used for swapping is a file called swap file. Consequently your computer is still working but very slowly. Either one has to close any unnecessary program or to add more RAM to the computer. To do this you have to physically add memory boards or change them for higher capacity ones, making sure you get the same type of RAM.

          That additional memory that is being swapped with the hard disk is called virtual memory.

          So we got very fast memory on one side and virtual memory on the other side which is much slower but very handy when memory lacks...


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