Random Access Memory:
The access of data from a storage device falls roughly into two categories: sequential access and random access. Random access means that you may quickly and precisely address a particular data location within the device, and non-random simply means that you may not. A vinyl record platter is an instance of a random-access device: to skip to any song, you just place the stylus arm at whatever location on the record that you want (compact audio disks so the similar thing, only they do it automatically for you). Cassette tape, alternatively, is sequential. You ought to wait to go past the other songs in sequence before you can access or address the song that you want to skip to. The process of storing a piece of data to a memory device is called writing, and the procedure of retrieving data is called reading. Memory devices permitting both reading and writing are equipped with a way to differentiate between the two tasks, so that no mistake is committed by the user (writing new information to a device whereas all you desired to do is see what was stored there).
Some devices do not permit for the writing of new data, and are buying "pre-written" from the manufacturer. Such is the case for vinyl records & compact audio disks, and it is typically referred to in the digital world as read-only memory, or ROM. Cassette video and audio tape, alternatively, may be re-recorded (re-written) or purchased blank and recorded fresh by the user. This is frequently called read-write memory. Another distinction to be made for any specific memory technology is its data storage permanence without power or volatility. Several electronic memory devices store binary data using circuits that are either latched in a "high" or "low" state, and this latching effect holds only as long as electric power is maintained to those circuits. Such memory would be appropriately referred to as volatile. Storage media like magnetized disk or tape is nonvolatile, because no source of power is required to maintain data storage. This is frequently confusing for new students of computer technology, because typically the volatile electronic memory utilized for the construction of computer devices is commonly and distinctly referred to as RAM (Random Access Memory).