Page 320 - DCAP103_Principle of operating system

Unit 10: Introduction of Windows and its Programming

by Microsoft, a tiny startup, mostly known at that time for its BASIC interpreter used on 8080 Notes
and Z-80 systems. This operating system consisted of 8 KB of memory resident code and was
closely modeled on CP/M, a tiny operating system for the 8-bit 8080 and Z80 CPUs. Two years
later, a much more powerful 24-KB operating system, MS-DOS 2.0, was released. It contained
a command line processor (shell), with a number of features borrowed from UNIX.
When Intel came out with the 286 chip, IBM built a new computer around it, the PC/AT, released
in 1986. AT stood for “Advanced Technology”, because the 286 ran at a then impressive 8 MHz
and could address-with great difficulty-all of 16 MB of RAM. In practice, most systems had at
most 1 MB or 2 MB, due to the great expense of so much memory. The PC/AT came equipped
with Microsoft’s MS-DOS 3.0, by now 36 KB. Over the years, MS-DOS continued to acquire new
features, but it was still a command-line oriented system.

Give the command of make directory in the DOS.

10.1.2 Windows 95/98/ME
Inspired by the user interface of the Apple Lisa, the forerunner to the Apple Macintosh,
Microsoft decided to give MS-DOS a graphical user interface (shell) which is called Windows.
Windows 1.0, released in 1985, was something of a dud. Windows 2.0, designed for the PC-AT
and released in 1987, was not much better. Finally, Windows 3.0 for the 386 (released in 1990),
and especially its successors 3.1 and 3.11, caught on and were huge commercial successes. None
of these early versions of Windows were true operating systems, but more like graphical user
interfaces on top of MS-DOS, which was still in control of the machine and the file system. All
programs ran in the same address space and a bug in any one of them could bring the whole
system to a grinding halt.
The release of Windows 95 in August 1995 still did not completely eliminate MS-DOS, although it
transferred nearly all the features from the MS-DOS part to the Windows part. Together, Windows
95 and the new MS-DOS 7.0 contained most of the features of a full-blown operating system,
including virtual memory, process management, and multiprogramming. However, Windows
95 was not a full 32-bit program. It contained large chunks of old 16-bit assembly code (as well
as some 32-bit code) and still used the MS-DOS file system, with nearly all its limitations. The
only major change to the file system was the addition of long file names in place of the 8 + 3
character file names allowed in MS-DOS.

Even with the release of Windows 98 in June 1998, MS-DOS was still there (now called
version 7.1) and running 16-bit code. Although yet more functionality migrated from the MS-DOS
part to the Windows part, and a disk layout suitable for larger disks was now standard, under
the hood, Windows 98 was not much different from Windows 95. The main difference was the
user interface, which integrated the desktop and the Internet more closely. It was precisely this
integration that attracted the attention of the U.S. Deptartment of Justice, which then sued Microsoft
claiming that it was an illegal monopoly, an accusation Microsoft vigorously denied. In April 2000,
the U.S. Federal court agreed with the government. In addition to containing a large lump of old
16-bit assembly code in the kernel, Windows 98 had two other serious problems. First, although
it was a multiprogramming system, the kernel itself was not reentrant. If a process was busy in
manipulating some kernel data structure and then suddenly its quantum ran out and another
process started running, the new process might find the data structure in an inconsistent state.
To prevent this type of problem, after entering the kernel, most processes first acquired a giant

LOVELY PROFESSIONAL UNIVERSITY 313