Computer Memory

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Computer Memory

The memory of Computer:

    1. A memory or store is required in a computer to store programs and the data processed by programs. A memory is made up of a large number of cells with each cell capable of storing one bit. The cells may be organized as a set of addressable words each word storing a sequence of bits.One such organization called Random Access Memory(RAM), is used as the main memory of computers. Another organization arrange cells in a linear sequence to form a serial access memory.

Memory Cell:

    1. A memory cell may be defined as a device that can store a symbol selected from a set of symbols and may be characterized by the following properties: The number of stable states in which it can be placed. Whether a cell can store a symbol indefinitely even when power is turned off. Whether a symbol, once written can only be read and not changed.

Memory Organization:

    1. Memory cells fabricated using current technology can be placed in one out of two stable states. we call these cells binary cells and each cell can store a binary digit. One of two stable states is used to represent binary 0 and the other binary 1.

Read-Only Memory:

    1. There are random access memories in which data words are permanently written during fabrication. A word can later be read from the memory by specifying its address. The contents of the word cannot, however, be altered. such memory is called a Read-Only Memory(ROM). Reading from a ROM should be non-destructive.

Flash Memory:

    1. Flash memory is a variety of EEPROM. It does not use the same technology as the EEPROM and has different features. However, it also uses semiconductors is non-volatile and is a fast read-slow write device just like EEPROM.

NOR flash Memory:

    1. NOR flash memory is a random access memory similar to EEPROM. We can thus address an individual word or a byte to read. However, we cannot erase a single byte.

NAND Flash Memory:

    1. Unlike NOR flash, NAND flash memory is not random access memory. It is however non-volatile and fast-slow write memory. A NAND flash is organized as a set of pages where each page is typically 512 to 2048 bytes.

Serial Access Memory:

    Consider the organization of memory cells organization the output of the cell is the input to the next cell.A read signal places the contents of each of the cells on the respective output lines. A write signal following this read signal will store these bits in the respective next cells.