Organization of the file system
binary-to run programs. This scheme has maximum flexibility and versatility.
Using the basic system calls (or library function I / O), users can drop
structured files. In particular, many DBMS store their databases in the ordinary
files.
The first step in structuring - storage file in a sequence of fixed-length
records, each of which is the internal structure. The central idea of the scheme -
operation reading on record, a record-operation and rewrite the record entirely
or adds. Previously record of 80 bytes (equal to the number of positions in the
punch card) or 132 characters (the width of the printer). In OS CP / M files
were sequences 128-symbolic records. With the introduction of CRT terminals,
this idea has lost popularity.
The third way of presenting files-sequence variable-length records, each of
which contains a key field in a fixed position inside the record. Basic
operation, in this case, take the record with a key value. Entries can be
consistently in the file (for example, as shown in value to a key fields) or in
a more complex manner. Using indexes files, records depository addresses,
allowing for quick access to a separate account (indeksno-posledovatelnaya
organization. Adding the new record in the file, a folder where it will be
determined not to put the user and the operating system. This method is used for
large mainframe commercial data processing. Types and file attributes An
important aspect of the file system design and OS - whether to support and
recognize file types. If so, it could help correct functioning of the OS, for
example, to prevent the withdrawal of the binary file to the printer.
To file types supported by modern operating system, include regular (ordinary)
files and directories. Normal (regular) files contain a user's information.
Directories (manuals, catalogs), system files, maintaining the structure of the
file system. The directory contains a list of files the motion, and fixed line
between files and their characteristics (attributes). We will consider the
directory below.
Remember that although the file management subsystem within the normal file
appears as a set of blocks external memory is provided for users of the
presentation file as a linear sequence of bytes. This presentation allows the
use of abstraction file when working with external devices, mezhprotsessnyh
interactions with the organization, etc. So, sometimes attributed to the files
other facilities operating system, for example, special symbolic files and block
special file named channels and socket with a file interface. These properties
are considered in other sections of the course.
Next, mainly discussed on conventional files.
Conventional (or regular) files actually are a set of blocks (possibly empty)
for the external memory device, which is supported file system. Such files can
contain both text information (usually in ASCII format) and the arbitrary binary
information.
Routine regular-files are ASCII and binary.
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