Information Technology Reference
In-Depth Information
Windows 95/98/NT use the full addressing capabilities of the 80x86/Pentium processors by
supporting a flat, linear memory model for 32-bit operating system functionality and Win32-
based applications. This linear addressing model simplifies the development process for ap-
plication vendors, and removes the performance penalties of a segmented memory architec-
ture.
H.6 Multiple file systems
Windows 95/98/NT supports a layered file system architecture that directly supports multiple
file systems (such as FAT and CDFS). Windows 95/98/NT have great performance im-
provements over Windows 3.
x
, for example:
•
Support for 32-bit protected-mode code when reading and writing information to and
from a file system.
•
Support for 32-bit dynamically allocated cache size.
•
Support for an open file system architecture to enhance future system support.
Figure H.7 shows the file system architecture used by Windows 95/98. It has the following
components:
•
IFS (installable file system) manager
. This is the arbiter for the access to different file
system components. On MS-DOS and Windows 3.
x
it was provided by interrupt 21h. Un-
fortunately, some add-on components did not run correctly and interfered with other in-
stalled drivers. It also did not directly support multiple network redirections (the IFS
manager can have an unlimited number of 32-bit redirectors).
•
File system drivers
. These provide support file systems, such as FAT-based disk de-
vices, CD-ROM file systems and redirected network devices. They are ring 0 compo-
nents, whereas Windows 3.
x
supported them through MS-DOS. The two enhanced file
systems are:
•
32-bit VFAT - the 'legacy' 16-bit FAT file system suffers from many problems, such
as the 8.3 file format. The 32-bit VFAT format is an enhanced form which works di-
rectly in the protected mode, and thus provides smooth multitasking as it is re-entrant
and multithreaded (a non re-entrant system does not allow an interrupt within an inter-
rupt). It uses the VFAT.VXD driver and uses 32-bit code for all file accesses. Another
advantage is that it provides for real-mode disk caching (VCACHE), where cache
memory is automatically allocated or deallocated when it is required (in Windows 3.
x
this was provided by the SMARTDRV.EXE program).
•
32-bit CDFS - the 32-bit, protected-mode CDFS format (as defined in the ISO 9660
standard) gives improved CD-ROM access and support for a dynamic cache (in Win-
dows 3.
x
the MSCDEX driver provided to access CD-ROMs).
•
Block I/O subsystem
. This is responsible for the actual physical access to the disk drive.
Its components are:
•
Input/Output Supervisor
(IOS) - this component provides for an interface between the
