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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 985
CHAP. 11
NTFS is a hierarchical file system, similar to the UNIX file system.
The sepa-
rator between component names is ‘‘\’’,however, instead of ‘‘/’’, a fossil inherited
from the compatibility requirements with CP/M when MS-DOS was created
(CP/M used the slash for flags).
Unlike UNIX the concept of the current working
directory, hard links to the current directory (.) and the parent directory (..) are im-
plemented as conventions rather than as a fundamental part of the file-system de-
sign. Hard links are supported, but used only for the POSIX subsystem, as is
NTFS support for traversal checking on directories (the ‘x’ permission in UNIX).
Symbolic links in are supported for NTFS.
Creation of symbolic links is nor-
mally restricted to administrators to avoid security issues like spoofing, as UNIX
experienced when symbolic links were first introduced in 4.2BSD.
The imple-
mentation of symbolic links uses an NTFS feature called
reparse points
cussed later in this section).
In addition, compression, encryption, fault tolerance,
journaling, and sparse files are also supported.
These features and their imple-
mentations will be discussed shortly.
11.8.2 Implementation of the NT File System
NTFS is a highly complex and sophisticated file system that was developed
specifically for NT as an alternative to the HPFS file system that had been devel-
oped for OS/2.
While most of NT was designed on dry land, NTFS is unique
among the components of the operating system in that much of its original design
took place aboard a sailboat out on the Puget Sound (following a strict protocol of
work in the morning, beer in the afternoon).
Below we will examine a number of
features of NTFS, starting with its structure, then moving on to file-name lookup,
file compression, journaling, and file encryption.
File System Structure
Each NTFS volume (e.g., disk partition) contains files, directories, bitmaps,
and other data structures.
Each volume is organized as a linear sequence of blocks
(clusters in Microsoft’s terminology), with the block size being fixed for each vol-
ume and ranging from 512 bytes to 64 KB, depending on the volume size.
NTFS disks use 4-KB blocks as a compromise between large blocks (for efficient
transfers) and small blocks (for low internal fragmentation).
Blocks are referred to
by their offset from the start of the volume using 64-bit numbers.
The principal data structure in each volume is the
Master File Table
which is a linear sequence of fixed-size 1-KB records.
Each MFT record describes
one file or one directory.
It contains the file’s attributes, such as its name and time-
stamps, and the list of disk addresses where its blocks are located.
If a file is ex-
tremely large, it is sometimes necessary to use two or more MFT records to con-
tain the list of all the blocks, in which case the first MFT record, called the
, points to the additional MFT records.
This overflow scheme dates back to

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