Source : Free On-Line Dictionary of Computing

random-access memory
     
         (RAM) (Previously "direct-access memory").  A data
        storage device for which the order of access to different
        locations does not affect the speed of access.  This is in
        contrast to, say, a {magnetic disk}, {magnetic tape} or a
        {mercury delay line} where it is very much quicker to access
        data sequentially because accessing a non-sequential location
        requires physical movement of the storage medium rather than
        just electronic switching.
     
        The most common form of RAM in use today is built from
        {semiconductor} {integrated circuit}s, which can be either
        static ({SRAM}) or dynamic ({DRAM}).  In the 1970s magnetic
        {core} memory was used.  RAM is still referred to as core by
        some old-timers.
     
        The term "RAM" has gained the additional meaning of
        read-write.  Most kinds of semiconductor {read-only memory}
        (ROM) are actually "random access" in the above sense but are
        never referred to as RAM.  Furthermore, memory referred to as
        RAM can usually be read and written equally quickly
        (approximately), in contrast to the various kinds of
        {programmable read-only memory}.  Finally, RAM is usually
        volatile though {non-volatile random-access memory} is also
        used.
     
        Interestingly, some {DRAM} devices are not truly random access
        because various kinds of "{page mode}" or "column mode" mean
        that sequential access is faster than random access.
     
        (1995-12-05)