MECH 2301 Lecture Notes - Lecture 9: Bitstream, Computer File, Management System
20 May 2018
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MECH 2301 Lecture 9 Notes
Introduction
Single-Field Logical File
• Just as there is no reason to assume that a paper record will fit exactly on a single sheet
of paper
• There is no reason to assume that the size of the logical records within the computer file
corresponds to the physical in any particular way
• Although on some computer systems it may.
• This is an issue to which we shall return shortly.
• Consider again, for example, the file shown
• Another representation of this file, more akin to the means used physically for its
storage, is shown
• As another example, the program file mentioned earlier could be interpreted as a single-
record, single-field logical file, with one long variable field in the record.
• Physically, the file might be stored as a sequence of physical blocks, accessed one after
another to retrieve the program.
• Many word processors also treat files this way.
• Files of these types are frequently loaded entirely into memory as a single unit.
• Different file management systems exhibit a range of capabilities in the ways in which
they represent files logically.
• Some operating systems recognize and manipulate several different types of files and
record structures
• While others simply treat all files as streams of bytes and leave it to utility and
application programs to determine the meaning of the data within the file.
• The file managers in Linux and Windows
• For example, differentiate only between directories and byte stream files.
• On these systems, program and data files are treated identically by the file manager.
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