PRESENTATION

Primary memory

What is Primary memory ?

It is relatively a large memory . This memory is used for program and data storage during computer operation . Location in main memory can be accessed directly and rapidly by the CPU . The technology used for main memory is based on semiconductor technology .

Types of primary memory

Read only memory (ROM) Programmable read only memory (PROM) Erasable programmable read only memory (EPROM) Electrically erasable programmable read only

memory (EEPROM) Random access memory (RAM)Cache memory

Read only memory

ROM is used for storing programs and data permanently . The data and programs required for some applications are permanently store in the ROM chip . Thus a user may read a program or data from ROM but may not write on ROM .

Programmable read only memory

PROMs are blank chip which have nothing recorded on them . Once instruction or data recorded into the chip by a special programming device . The PROM permanently stores the information like ROM .

Erasable programmable read only memory

EPROM chip can be programmed as the PROM chip , but they can be erased and reprogrammed by a special programming device . The content of an EPROM chip can be erased by exposing it to ultraviolet light .

Electrically erasable programmable read only memory

EEPROM is similar to EPROM expect that it is erased by applying electrical pulses to the chip . It is possible to reprogram an EEPROM chip via keyboard commands without removing the chip from the computer .

Random access memory

RAM is temporary storage that can be read from or write into by the user . RAM is used primarily to store user programs and data . The content of RAM is generally volatile , and is lost when power is removed . When the system is powered up Programs and data to be used must be read into RAM through an input device .

Types of RAM

Static RAM Dynamic RAM

Static RAM

SRAM stands for static random access memory . it’s speed is high . It doesn’t require refreshing and generally used for cache . SRAMs control complexity is less , it is a costly instrument .

Dynamic RAM

DRAM stands for dynamic random access memory . It is works slowly . It requires refreshing periodically and used for main memory . DRAMs control complexity is high , it’s cost is low .

Cache memory

As mentioned earlier the memory is slower then the CPU . System performance suffers when a fast device must wait to access data from a memory system . This may be an i/o device or cpu , and the memory system may be main memory or an external device . Because computer users always seem to want larger memories , computer designers must carefully decide memory cost and performance .