Organization of the file system
waiting until the required traffic and do block will be head and the proper
reader unit. This requires a significant amount of time (tens of milliseconds).
In modern computers appeal to the disk around 100000 slower than resort to
memory. Thus, the computational complexity of algorithms criterion working with
external memory is the number of hits to the disk.
This chapter discussed the structure, naming, file protection, the transactions
authorized over the files, the file archive. Problems allocating disk space,
ensuring productive work file system and a number of other designers interested
in the system, made in the following chapter. Filenames File-abstract objects.
They provide users with the ability to retain information, concealing from him
the details of how and where it is stored, and how the disks actually interact.
Probably one of the most important characteristics of any abstract mechanism is
a way for naming objects, which he manages. When the process creates a file, it
gives the file name. Following the completion of the file continues to exist,
and through his name may be made available to other processes.
Many OS supports the names of two parts (name + extensions), for example progr.c
(file containing the text of the program in the language Si) or autoexec.bat (file
containing commands command language interpreter). File Type expansion OS allows
him to organize the work of various applications in accordance with pre-defined
agreements.
Usually OS impose some restrictions, as used in the name of characters, and the
length of the name. For example, the Unix OS-sensitive when you enter the file
name (case sensitive), while MS-DOS not. In popular FAT file system names
limited to a certain length of the scheme 8.3 (8 characters proper name, 3-character
extension name). Modern file systems tend to be supported by more user-friendly
symbolic long file names. Thus, in accordance with the standard POSIX, in the
UNIX OS allowed names length to 255 characters, the same applies to the length
of file names and OS Windows NT file system to NTFS. File Structure As already
mentioned, the programmer sees the file as a set of logical records. Logical
Record is the smallest data element, which can operate in exchange programs with
an external device. Even if the physical exchange of the device is carried out
large units (usually blocks), the operating system provides the programmer
access to a separate logical record.
OS supported several options to structure the files.
First, the file as unstructured sequence of bytes. For example, file systems and
UNIX OS MS-DOS file is the simplest structure of the logical sequence of single-records.
OS not undertake any interpretation of these bytes. Nevertheless, with the OS
file systems of this type must maintain at least one structure
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