Page 10 - DCAP103_Principle of operating system

Unit 1: Operating System

systems are used on most, but not all, computer systems. The simplest computers, including the Notes
smallest embedded systems and many of the first computers, did not have operating systems.
Instead, they relied on the application programs to manage the minimal hardware themselves,
perhaps with the aid of libraries developed for the purpose. Commercially-supplied operating
systems are present on virtually all modern devices described as computers, from personal
computers to mainframes, as well as mobile computers such as PDAs and mobile phones.

1.1 History of Operating Systems

An operating system (OS) is a software program that manages the hardware and software
resources of a computer. The OS performs basic tasks, such as controlling and allocating memory,
prioritizing the processing of instructions, controlling input and output devices, facilitating
networking, and managing files.
The first computers did not have operating systems. However, software tools for managing the
system and simplifying the use of hardware appeared very quickly afterwards, and gradually
expanded in scope. By the early 1960s, commercial computer vendors were supplying quite
extensive tools for streamlining the development, scheduling, and execution of jobs on batch
processing systems. Examples were produced by UNIVAC and Control Data Corporation,
amongst others.
Through the 1960s, several major concepts were developed, driving the development of operating
systems. The development of the IBM System/360 produced a family of mainframe computers
available in widely differing capacities and price points, for which a single operating system
OS/360 was planned (rather than developing ad hoc programs for every individual model).
This concept of a single OS spanning an entire product line was crucial for the success of
System/360 and, in fact, IBM’s current mainframe operating systems are distant descendants of
this original system; applications written for the OS/360 can still be run on modern machines.
OS/360 also contained another important advance: the development of the hard disk permanent
storage device (which IBM called DASD). Another key development was the concept of time-
sharing: the idea of sharing the resources of expensive computers amongst multiple computer
users interacting in real time with the system. Time sharing allowed all of the users to have
the illusion of having exclusive access to the machine; the Multics timesharing system was
the most famous of a number of new operating systems developed to take advantage of the
concept. Multics, particularly, was an inspiration to a number of operating systems developed
in the 1970s, notably Unix. Another commercially popular minicomputer operating system was
VMS. The first microcomputers did not have the capacity or need for the elaborate operating
systems that had been developed for mainframes and minis; minimalistic operating systems were
developed. One notable early operating system was CP/M, which was supported on many early
microcomputers and was largely cloned in creating MS-DOS, which became wildly popular as
the operating system chosen for the IBM PC (IBM’s version of it was called IBM-DOS or PC-
DOS), its successors making Microsoft one of the world’s most profitable companies. The major
alternative throughout the 1980s in the microcomputer market was Mac OS, tied intimately to
the Apple Macintosh computer.
By the 1990s, the microcomputer had evolved to the point where, as well as extensive GUI
facilities, the robustness and flexibility of operating systems of larger computers became
increasingly desirable. Microsoft’s response to this change was the development of Windows
NT, which served as the basis for Microsoft’s entire operating system line starting in 1999. Apple
rebuilt their operating system on top of a Unix core as Mac OS X, released in 2001. Hobbyist-
developed reimplementations of Unix, assembled with the tools from the GNU project, also
became popular; versions based on the Linux kernel are by far the most popular, with the
BSD derived UNIXes holding a small portion of the server market. The growing complexity of
embedded devices has a growing trend to use embedded operating systems on them.

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