What is the memory used for?

Answer 1

Permanent storage tends to be slow. For disks, there there is rotational delay while the disk rotates beneath the read/write head, and seek delay as the head moves across the disk from track to track. Tape is even worse, and little used anymore. The memory serves as the storage area where programs and data are loaded. The programs are executed from memory. Each program instruction is loaded into the central processing unit (CPU) and executed there. Instructions are commands, such as add the contents of two registers, or branch to a location in the memory, or fetch the data at a particular location in memory, etc.

Memory tends to be much smaller than disk storage. Currently typical home PC disk capacities range from a hundred gigabytes up to a terabyte (a trillion bytes). A typical digital photograph takes up approximately 2 megabytes. In a hundred gigabytes you could store roughly 50,000 photographs. But computer memory generally ranges from 256 megabytes to a gigabyte. Some of this space will be consumed by operating system software, and some of it by programs. Programs that are executing in the background take up some of the computer's memory, like the program that checks your e-mail, and so on. Image editing software takes up a lot of memory space. So if your computer has 512 megabytes of RAM (random access memory), maybe half of that would be left over for data, or less. JPG images are probably translated into bit mapped format in the computer's memory to make manipulation easier--which would leave even less space--maybe room for only a handful of photos. You will get an idea because the computer will suddenly start running a lot slower when too many images are loaded into memory, as some of that memory will be swapped back out to disk as you switch between tasks.