Memory Organisation And Random Access Memory Computer Science

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Memory stores, instructions and data. Memory is of two types, primary memory and secondary memory. Instruction or data given by input devices is first getting stored in the primary memory. Further user saves processed (executed) data in the secondary memory. Primary memory is temporary and secondary memory is permanent.

Primary memory is the main memory of the computer system. It is faster than secondary memory. It directly communicates with CPU.

3.2 Memory Unit

Computer uses several types of memories to save instructions and data. Computer uses RAM and ROM as primary memory.

RAM is a primary memory used in the computer. It is volatile since its content is accessible only as long as the computer is ON. The content of RAM is cleared as soon as computer is powered OFF. SRAM is used as cache memory in the computer system. A DRAM is used as main memory of the computer system. Types of DRAM are as SDRAM, DDRAM and RDRAM.

ROM (Read Only Memory) is non-volatile; read only memory unit. It used to store firmware, for example BIOS program. User can only read content of the ROM, can not write or modify.

A secondary memory is non-volatile. A devices used as secondary memory are HDD, FDD, CD, DVD, Tape drives and so on.

FDD (Floppy Disk Drives) used as magnetic, portable memory device. It stores maximum 1.44 MB data. Earlier it used to transfer data among computer systems.

HDD (Hard Disk Drives) are fixed, magnetic memory device. It is vital in the computer system because user saves permanent data on the HDD. Storage capacity of HDD is vendor specific.

CDs and DVDs are optical memory units used for transferring data and programs among the computers. CDs are available in the size 650MB, DVDs are available up to 4 GB in a size.

Tape drives are usually used for data backup purpose.

MemoryPrimary MemorySecondary MemoryRAMROMSRAMDDRAMSDRAMRDRAMPROMHDDDRAMEPROMEEPROMFDDCDDVDTape drivesFigure 3.1 Memory Types

3.3

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