Memory Locations and Addresses

MEMORY LOCATIONS AND ADDRESSES:- Number and character operands, as well as instructions, are stored in the memory of a computer. The memory consists of many millions of storage cells, each of which can store a bit of information having the value 0 or 1. Because a single bit represents a very small amount of information, bits are seldom handled individually. The usual approach is to deal with them in groups of fixed size. For this purpose, the memory is organized so that a group of n bits can be stored or retrieved in a single, basic operation. Each group of n bits is referred to as a word of information, and n is called the word length. The memory of a computer can be schematically represented as a collection of words as shown in figure (a).Modern computers have word lengths that typically range from 16 to 64 bits. If the word length of a computer is 32 bits, a single word can store a 32-bit 2’s complement number or four ASCII characters, each occupying 8 bits. A unit of 8 bits is called a byte .Accessing the memory to store or retrieve a single item of information, either a word or a byte, requires distinct names or addresses for each item location. It is customary to use numbers from 0 through 2K -1, for some suitable values of k, as the addresses of successive locations in the memory. The 2k addresses constitute the address space of the computer, and the memory can have up to 2k addressable locations. 24-bitaddress generates an address space of 224(16,777,216) locations. A 32-bit address creates an address space of 232or 4G (4 giga) locations.
MEMORY OPERATIONS:-
Both program instructions and data operands are stored in the memory. To execute an instruction, the processor control circuits must cause the word (or words) containing the instruction to be transferred from the memory to the processor. Operands and results must also be moved between the memory and the processor. Thus, two basic operations involving the memory are needed, namely, Load (or Read or