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    Computer Memory

    Memory of Computer: A memory or store is required in a computer to store programs and the data processed by programs.A memory is made up of large number of cells with each cell capable of storing one bit.The cells may be orgenised as a set of addressable words each word storing a seqeunce of bits.In one such organisation called Random Access Memory(RAM),is used as the main memory of computers.Another organisaton arrange cells in a linear sequence to form a serial access memory.
    Memory Cell:A memory cell may be defined as adevice which can store a symbol selected from a set of symbols and may be charaterized byh the following properties:The number of stable states in which it can be placed.Whether a cell can store a symbol in definitely even when power is turned off.Whether a symbol,once written can only be read and not changed.
    Memory Organization: Memory cells febricatd 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 the binary 0 and the other binary 1.
    Read Only Memory:There are random access memories in which data words are permanently written during fabrication.A word can later be read fromn the memory by specifying its address.The contents of the word cannot ,however,be altered. such a memory is called a Read Only Memory(ROM).Reading from a ROM should be non-destructive.
    Flash Memory:Flash memory is variety of EEPROM.It does nor 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: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:Unlike NOR flash,NAND flash memory is not a 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 cell is the input to next cell.A read signbal places the contents of each of the cells on the respective output lines.A write signal foloewing this read signal will store these bits in the respective next cells.

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