What is Computer Memory?

Computer memory:

Main storage is also called memory or internal memory (to distinguish from external memory, such as hard drives).
RAM is Random Access Memory, and is the basic kind of internal memory. RAM is called "random access" because the processor or computer can access any location in memory (as contrasted with sequential access devices, which must be accessed in order). RAM has been made from reed relays, transistors, integrated circuits, magnetic core, or anything that can hold and store binary values (one/zero, plus/minus, open/close, positive/negative, high/low, etc.). 

Most modern RAM is made from integrated circuits. At one time the most common kind of memory in mainframes was magnetic core, so many older programmers will refer to main memory as core memory even when the RAM is made from more modern technology. Static RAM is called static because it will continue to hold and store information even when power is removed. Magnetic core and reed relays are examples of static memory. Dynamic RAM is called dynamic because it loses all data when power is removed. Transistors and integrated circuits are examples of dynamic memory. It is possible to have battery backup for devices that are normally dynamic to turn them into static memory.

ROM is Read Only Memory (it is also random access, but only for reads). ROM is typically used to store things that will never change for the life of the computer, such as low level portions of an operating system. Some processors (or variations within processor families) might have RAM and/or ROM built into the same chip as the processor (normally used for processors used in standalone devices, such as arcade video games, ignition systems, etc.). EPROM is Erasable Programmable Read Only Memory, a special kind of ROM that can be erased and reprogrammed with specialized equipment (but not ATMS, microwave ovens, car by the processor it is connected to).

EPROMS allow makers of industrial devices (and other similar new equipment) to have the benefits of ROM, yet also allow for updating or upgrading the software without having to buy new ROM and throw out the old (the EPROMS are collected, erased and rewritten centrally, then placed back into the machines).

Memory types:

Storage refers to the media and methods used to keep information available for later use. Some things will be needed right away while other won't be needed for extended periods of time. So different methods are appropriate for different uses.

Primary Storage is Main Memory:

This keeps track of what is currently being processed.

It's volatile. (power of erases all data)
For Main Memory, computers use RAM, or Random Access Memory. This uses memory chips and is the fastest but most expensive type of storage.

Secondary Storage is called Auxiliary Storage
This is what is not currently being processed. This is the stuff "filed away", but ready to be pulled out when needed.
It is nonvolatile. (power off does not erase)

Auxiliary Storage is used for:

So, Auxiliary Storage is where you put last year's tax info, addresses for old customers, programs you may or may not ever use, data you entered yesterday - everything that is not being used right now.

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