The four main types of primary storage are (1) register, (2) cache memory, (3) random access
memory (RAM), and (4) read-only memory (ROM). You learn about each type of primary
storage next.
Registers
are part of the CPU. They have the least capacity, storing extremely limited amounts
of instructions and data only immediately before and after processing.
Cache memory
is a type of high-speed memory that enables the computer to temporarily store
blocks of data that are used more often and that a processor can access more rapidly than main
memory (RAM). Cache memory is physically located closer to the CPU than RAM. Blocks that
are used less often remain in RAM until they are transferred to cache; blocks used infrequently
remain in secondary storage. Cache memory is faster than RAM because the instructions travel a
shorter distance to the CPU.
Random access memory (RAM)
is the part of primary storage that holds a software program
and small amounts of data for processing. When you start most software programs (such as
Microsoft Word) on your computer, the entire program is brought from secondary storage into
RAM. As you use the program, small parts of the program's instructions and data are sent into
the registers and then to the CPU. Compared with the registers, RAM stores more information
and is located farther away from the CPU. However, compared with secondary storage, RAM
stores less information and is much closer to the CPU.
RAM is temporary and, in most cases,
volatile
—that is, RAM chips lose their contents if the
current is lost or turned off, as from a power surge, brownout, or electrical noise generated by
lightning or nearby machines.
Most of us have lost data at one time or another due to a computer “crash” or a power failure.
What is usually lost is whatever is in RAM, cache, or the registers at the time, because these
types of memory are volatile. Therefore, you need greater security when you are storing certain
types of critical data or instructions. Cautious computer users frequently save data to nonvolatile
memory (secondary storage). In addition, most modern software applications have autosave
functions. Programs stored in secondary storage, even though they are temporarily copied into
RAM when they are being used, remain intact because only the copy is lost, not the original.
Read-only memory (ROM)
is the place—actually, a type of chip—where certain critical
instructions are safeguarded. ROM is nonvolatile, so it retains these instructions when the power
to the computer is turned off. The read-only designation means that these instructions can only
be read by the computer and cannot be changed by the user. An example of ROM is the
instructions needed to start or “boot” the computer after it has been shut off.
