Difference between pages "File" and "Word"

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A '''file''' is an agglomeration of information - perhaps data (including [[source code]], which is data from the perspective of the computer), sometimes [[object code]] - saved on [[secondary storage]], usually in a [[file system]].
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A '''word''' is the basic unit of data on which a [[Central Processing Unit|CPU]] operates; on many machines it is the size of an [[instruction]]. [[Main memory]] addresses used to name words, but contemporary practise is to give each [[byte]] in main memory its own address.
  
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Depending on the [[operating system]], a file may be presented to the user as a simple array of bytes or words (as in all [[Unix]] systems), or it may have a more structured form, with [[record]]s.
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Words are now usually a power-of-two multiple of an 8-bit byte in size, but in early computers, other word sizes were common. 36 bits was a very popular size on early [[mainframe]]s, such as the [[IBM 704]] and its descendants, the [[Honeywell 6000 series‎‎]], and the [[PDP-10]] family. However, small word sizes were common too, e.g. the 12-bit words of the [[PDP-8 family]].
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Although the file system may break up the contents of a file into different physical [[disk|blocks]], scattered across a [[disk]], this is purely internal, to simplify space allocation, and not visible to the user, to whom the file still appears as a unitary object. (In fact, some file systems, such as the [[BSD Fast File System]] do make an effort to keep the blocks of a file in close physical proximity, for access speed reasons.)
 
  
 
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Revision as of 20:35, 22 November 2019

A word is the basic unit of data on which a CPU operates; on many machines it is the size of an instruction. Main memory addresses used to name words, but contemporary practise is to give each byte in main memory its own address.

Words are now usually a power-of-two multiple of an 8-bit byte in size, but in early computers, other word sizes were common. 36 bits was a very popular size on early mainframes, such as the IBM 704 and its descendants, the Honeywell 6000 series‎‎, and the PDP-10 family. However, small word sizes were common too, e.g. the 12-bit words of the PDP-8 family.

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