Explain about computer memory

Explain about computer memory
Ans:Memory is a predefined working place, where data and information are kept for processing and it is cleared after the job is accomplished or as switched off. A bit is an elementary unit of the memory. It is also known as primary or main memory and the data is dump for future reference to secondary memory i.e. hard disk.
We need primary memory for
· Loading operating system
· Any program (application software) has to be loaded into RAM (Primary Memory) for execution
· Data and information is saved into RAM until it is finally saved into permanent memory.
ROM
· Semiconductor chip
· Non-volatile
· Set by manufacturers
· Contain micro programs or control instructions
· Responsible for starting computer
· Cannot be changed or written program
· Permanently attached to board
· PROM (User can reduce lengthy program to micro)
· EPROM (can be erased & reprogrammed)
· EEPROM (can be reprogrammed with special electrical pulses)
RAM
· Semiconductor chip
· Volatile
· Steady electricity supply
· Directly accessed by CPU(50nano sec)
· DRAM (for larger memory capacity, for very short time/refreshed, cheaper, 16 bytes or more is by it, a transistor on-off, a capacitor-storing electric charge)
· SRAM (data is retained till power on, high cost, higher speed as computer DRAM, more capacitors and transistors)
CACHE MEMORY
· between CPU & RAM
· Access time 10 nano sec
· Costlier than RAM
· less capacityto store data & instruction for immediate execution