Overview of a Computer - Primary Storage

Overview of a Computer - Primary Storage

·        Primary storage, also known as main memory or RAM (random access memory) is used to store information for immediate access by the Central Processing Unit (CPU)

·        Memory can be viewed as a series of memory cells with each cell having its own individual address

·        E.g., think of a bank of mailboxes at a post office

·        The information contained in a memory cell is called the contents of that cell

·        Memory cells can be used to store data, such as characters or numbers

·        Internally, of course, they are all numbers, but we can choose to interpret some numbers as characters

·        They can also be used to store program instructions

·        These are “special” numbers that are meaningful to a CPU!

·        The smallest unit of computer storage is a bit, as in binary digit

·        Most computers group bits together to form larger entities

·        E.g., 8 consecutive bits  often form a byte and 32 consecutive bits often form a word

·        A word on an Intel 286 computer is 16 bits or 2 bytes

·        A word on an Intel 386, 486, and Pentium computers is 32 bits or 4 bytes

·        The next generation of Intel computers (e.g. the Merced) will use 64 bit words, i.e. 8 bytes

·        The DEC Alpha computer is currently using 64 bit words

·        Many mainframe computers, such as the Unisys A-Series, use 48 bit words

·        Memory cells in a computer are typically one byte or one word in size

·        A word is a unit of information that can be transferred to and from memory

·        A kilobyte of memory, as in 1K, is 1024 bytes of memory

·        A megabyte of memory, as in 1M, is 1024K of memory, or 2^20 bytes

·        A gigabyte of memory, as in 1G, is 1024M of memory, or 2^30 bytes

·        Note that a 32 bit word can represent 2^32 different possible values