# In many computers the main memory is also designed in

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Unformatted text preview: h with a small data shovel and the user of a machine having larger word length with a large data shovel. Even though they both may be shoveling at comparable speeds, the user with the smaller shovel will be slower because more shovelfuls are needed to move the same amount of data. Fixed and Variable Word-length Memory The main memory of some computers is designed to store a fixed number of characters (equal to its word-length in bytes) in each numbered address location. Such computers are said to be word-addressable, and they employ a fixed-word-length memory approach. In these computers, storage space is always allocated in multiples of word-length. So if a word addressable computer has a fixed word-length of 4 bytes (4 characters) then this computer will require one word (4 bytes) to store the word &quot;CAT&quot; and two words (8 bytes) to store the word &quot;BOMBAY&quot;. In many computers, the main memory is also designed in such a way that each numbered address can only store a single character (A, B, 1,2, +, -, etc.). Computers designed in this manner are said to be character-addressable and they employ a variable-word-length memory approach. Thus in these machines, only 3 bytes will be required to store the word &quot;CAT&quot; and only 6 bytes will be required to store the word &quot;BOMBAY&quot;. Figure 7.4 summarizes the difference between the fixed-word-length and variable-word-length memory approaches. Both the fixed and the variable word-length memory systems have their own merits and demerits. The fixed-word-length memory approach is normally used in large scientific computers for gaining speed of calculation. On the other hand, the variable-word-length approach is used in small business computers for optimizing the use of storage space. For example, let us consider a fixed-word-length machine with a word size of eight characters. If most of the data words to be stored are of less than five characters then more than half of the storage space will remain unused. This will not happen in case of a machine with...
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