TABLE OF CONTENTS Devices that can store information or settings, either permanently (non-volatile memory) or while the power supply remains on (volatile memory), form an essential part of almost every modern electronic system. Even equipment that has no apparent programmable functions may contain devices that are configured at or after assembly, reducing the inventory that the manufacturer has to keep and making designs more flexible by allowing modifications during production.
Solid state or integrated circuit memory devices for microprocessors and other computer applications fall into two categories. One type is memory that is not changed in normal operation and whose contents are not lost if power is turned off (non-volatile), typically containing the program commands and data that determine how a system operates. This type of memory tends to be called read-only memory ( ROM), and historically ROMs were produced by manufacturing chips with the data defined during manufacture of the silicon, by configuring the connections of one or more layers of poly-silicon or metal. Even in very high volume production equipment, true ROM is rare; today, most systems use a form of programmable read-only memory (PROM) these are often reprogrammable, although not necessarily in the system in which they are used.
The other type of memory is volatile, and is referred to as random access memory (RAM). Most modern memory devices support random access; that is, data can be accessed or written to any location independent of the location of the previous read or write however, this was...
