Difference between RAM and ROM

1.      RAM 

(RAM pronounced ramm, acronym for Random Access Memory,): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM  and read from RAM.

This is in contrast to ROM, which permits you only to read data.

RAM can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes.

RAM is the most common type of memory found in computers and other devices, such as printers.

There are two basic types of RAM:

·         Dynamic RAM (DRAM)

·         Static RAM (SRAM)

The two types differ in the technology they use to hold data, dynamic RAM being the more common type.

Dynamic RAM needs to be refreshed thousands of times per second.

Static RAM does not need to be refreshed, which makes it faster; but it is also more expensive than dynamic RAM. Both types of RAM are volatile, meaning they hold data only when the power is on. When the power is off, RAM's contents are lost.

2.      ROM

 (Read Only Memory): Computers almost contain a small amount (a few thousands of bytes) of ROM that holds instructions for starting up/ booting the computer and perform diagnostics. Unlike RAM, ROM cannot be written to. In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be  referred to as read/write RAM and ROM as read-only RAM.

PROM (Pronounced prom, an acronym for Programmable Read Only Memory). A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.

The difference between a PROM and a ROM 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 PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

EPROM (Acronym for Erasable Programmable Read Only Memory and pronounced ee-prom).  An EPROM is a special type of ROM that can be erased by exposing it 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.

An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROM’s are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. His means that bugs can be removed and new versions installed shortly before deliver.

EEPROM (Acronym for Electrically Erasable Programmable Read Only Memory and pronounced double-ee-prom or e-e-prom). An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of RM, EEPROM is not as fast as RAM.

EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster.