In which memory, processor can communicate directly is called primary memory. This memory stores data or information temporarily. After processing data are stored into secondary memory. There are different types of primary memory such as-
ROM: Read only memory is shortly called ROM. The data stored in a ROM chip can only be read and used, they cannot be changed. This is why it is called read only memory. At the time of making ROM chip by the manufacturing company which data are stored, cannot be deleted, stored permanently. But now a day's data of some ROM chips can be changed or altered in some special ways.
Various types of ROM chips are described below.
Mask ROM: In which manufacture company, made ROM-Chip, they (that company) also write program own and delivered in the market. Later this program can never be changed.
PROM (Programmable Read Only Memory): In this case one manufacturing company makes only ROM chip and another company writes program. This chip is also unchangeable.
EPROM (Erasable Programmable Read Only Memory) : EPROM has a glass window, which covered with a label. Program can be changed by high-intensity ultra violet ray with the help of this glass window. Bright sunlight can cares EPROM. But no problem is raised in room-light.
EEPROM (Electricity Erasable Programmable Read Only Memory): EEPROM is more access able than EEPROM. This ROM can be changed or updated bit by bit through electricity, software or utility. At present EEPROM is used in PC as BIOS, which is introduced as Flash BIOS.
RAM: RAM is an important component of a computer. Acronym of RAM is Random Access Memory, which stores data program temporarily while computer os started on. This is why it is called temporary memory. While PC is started on, which works have been done by user, are stored by RAM. In any time from any place of it, we can read or write data, this is why it is called Random Access Memory. It is temporary because when electricity is gone, all the data of it is deleted. So this memory is also works or playing games minimum 128-256 MB RAM is needed. At present market different branded RAM of different capacity are available such as 128 MB, 256MB, and 512MB etc. Recently South Korean Samsung Electronics has improved of 1GB DRAM which is proposed to deliver in market in this current year.
Mainly RAM has two categories-
(a) DRAM (Dynamic RAM): This type of RAM stores charges into mini capacitor and saves data refreshing through external circuit.
(b) SRAM (Static RAM): Static RAM can keep data in keeping with power supply. Its speed is comparatively higher and it is more expensive to make because flip-flop circuit makes it, which is expensive. Generally this RAM is for cache memory.
Secondary Memory or Auxiliary Memory: In which memory processor cannot communicate directly is called secondary memory. In this memory data are stored permanently. As secondary memory Floppy disk, compact disk, Magnetic tape etc. are used.