Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor devices. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.
RAM stands for Random Access Memory. It is a form of data storage that can be accessed randomly at any time, in any order, and from any physical location in contrast to other storage devices, such as hard drives, where the physical location of the data determines the time taken to retrieve it. RAM is measured in megabytes and the speed is measured in nanoseconds and RAM chips can read data faster than ROM.
What is ROM?
ROM stands for Read-Only Memory. It is an example of nonvolatile memory. It is a class of storage medium used in computers and other electronic devices. Read-Only Memory, also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. Several Types Of ROM:
- PROM (Programmable Read-Only Memory): The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.
- EPROM: Erasable Programmable Read-Only Memory: EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.
- EEPROM (Electrically Erasable Programmable Read-Only Memory): It also like other types of ROM, EEPROM is not as fast as RAM.