ROM stands for Read Only Memory and is typically used in computers to permanently hold data. There are only a few specific ways ROM can be reprogrammed. Unlike ROM, RAM (Random Access Memory) is continually reprogrammed and stores essential data required to run programs, such as information and calculations. There are many types of ROM and RAM, each designed and revised for better performance.
Read Only Memory (ROM)
Read Only Memory is constructed from "hard-wire logic," in a similar way to the processor, meaning that it cannot be reprogrammed or changed. This is because it is designed to perform a specific function, and does not need to be altered. An example of ROM is a commercial CD purchased from a store; the manufacturers do not want you to alter what is stored on the disk.
Programmable Read Only Memory (PROM)
Programmable Read Only Memory can be programmed using specific software only available to companies producing PROM chips. PROM can be likened to burning to a CD only once and reading from it many times.
Erasable Programmable Read Only Memory (EPROM)
Erasable Programmable Read Only Memory is ROM which can be read from and reprogrammed. This type of ROM can only be reprogrammed using a special type of ultra-violet light, and therefore is only reprogrammed by manufacturers.
Electronically Erasable Programmable Read Only Memory (EEPROM)
EEPROM is the most flexible type of ROM because it can be reprogrammed using software. Because of this, EEPROM is becoming the standard type of ROM used in consumer motherboards. EEPROM allows the easy "flashing" of motherboard memory when problems arise or updates are released.
Synchronous Dynamic Random Access Memory (SDRAM)
SDRAM is an old and slow type of Random Access Memory. It used to ship with old Pentium systems and is starting to die out.
Double Data Rate Synchronous Dynamic Random Access Memory (DDR-SDRAM)
DDR Random Access Memory transfers data twice per clock cycle, essentially doubling the amount of data transferred by SDRAM. DDR was introduced around 2001 and soon became the market standard.
Double Data Rate Revision 2 Synchronous Dynamic Random Access Memory (DDR2-SDRAM)
DDR2 Random Access Memory is similar to original DDR memory, with the addition of an external data bus to the memory modules. This allows the memory to operate at twice the clock rate, but at twice the latency. Therefore, DDR2 will operate at twice the speed of DDR memory. DDR2 memory was introduced in the second quarter of 2003.
Double Data Rate Revision 3 Synchronous Dynamic Random Access Memory
DDR3 Random Access Memory is the third revision to the original DDR module. According to MemoryX.net, DDR3 memory is faster than DDR2 and supports 8GB modules, whereas DDR2 memory only supports 4GB per module.