30. Electronic Computer Memory. Part 2 1149

There are two principal varieties of Computer main memory: random access memory or RAM¹ and read-only memory or ROM².

RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it.

ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely.

In a PC, ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset.

In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

¹RAM (random access memory) - память с произвольным доступом

²ROM (read-only memory) - постоянная память (память с нестираемой записью)