Page 11 - DCAP103_Principle of operating system

Principles of Operating Systems
Notes
4 LOVELY PROFESSIONAL UNIVERSITY
1.1.1 Today
Command line interface (or CLI) operating systems can operate using only the keyboard for input.
Modern OS’s use a mouse for input with a graphical user interface (GUI) sometimes implemented
as a shell. The appropriate OS may depend on the hardware architecture, specifically the CPU,
with only Linux and BSD running on almost any CPU. Windows NT has been ported to other
CPUs, most notably the Alpha, but not many. Since the early 1990s the choice for personal
computers has been largely limited to the Microsoft Windows family and the Unix-like family,
of which Linux and Mac OS X are becoming the major choices. Mainframe computers and
embedded systems use a variety of different operating systems, many with no direct connection
to Windows or Unix, but typically more similar to Unix than Windows.
• Personal computers
• IBM PC compatible — Microsoft Windows and smaller Unix variants (like Linux and BSD)
• Apple Macintosh — Mac OS X, Windows, Linux and BSD
• Mainframes — A number of unique OS’s, sometimes Linux and other Unix variants
• Embedded systems — A variety of dedicated OS’s, and limited versions of Linux or other
OS’s
1.1.2 Unix-like Family
The Unix-like family is a diverse group of operating systems, with several major subcategories
including System V, BSD, and Linux. The name “Unix” is a trademark of the Open Group which
licenses it for use to any operating system that has been shown to conform to the definitions
that they have cooperatively developed. The name is commonly used to refer to the large set
of operating systems which resemble the original Unix. Unix systems run on a wide variety of
machine architectures. They are used heavily as server systems in business as well as workstations
in academic and engineering environments. Free software Unix variants, such as Linux and BSD,
are increasingly popular. They are used in the desktop market as well, for example Ubuntu, but
mostly by hobbyists. Some Unix variants like HP’s HP-UX and IBM’s AIX are designed to run
only on that vendor’s proprietary hardware. Others, such as Solaris, can run on both proprietary
hardware and on commodity x86 PCs. Apple’s Mac OS X, a microkernel BSD variant derived
from NeXTSTEP, Mach, and FreeBSD, has replaced Apple’s earlier (non-Unix) Mac OS. Over
the past several years, free Unix systems have supplanted proprietary ones in most instances.
For instance, scientific modelling and computer animation were once the province of SGI’s IRIX.
Today, they are dominated by Linux-based.
The team at Bell Labs who designed and developed Unix went on to develop and Inferno, which
were designed for modern distributed environments. They had graphics built-in, unlike Unix
counterparts that added it to the design later did not become popular because, unlike many
Unix distributions.
1.1.3 Microsoft Windows
The Microsoft Windows family of operating systems originated as a graphical layer on top
of the older MS-DOS environment for the IBM PC. Modern versions are based on the newer
Windows NT core that first took shape in OS/2 and borrowed from OpenVMS. Windows
runs on 32-bit and 64-bit Intel and AMD computers, although earlier versions also ran on the
DEC Alpha, MIPS, and PowerPC architectures (some work was done to port it to the SPARC
architecture). As of 2004, Windows held a near-monopoly of around 90% of the worldwide
desktop market share, although this is thought to be dwindling due to the increase of interest
focused on open source operating systems. It is also used on low-end and mid-range servers,
supporting applications such as web servers and database servers. In recent years, Microsoft
has spent significant marketing and R&D money to demonstrate that Windows is capable of
running any enterprise application (see the TPC article).