Saturday, July 5, 2008

Some interesting trivia of operating system ! phew

A Glimpse of OS History

A Background

Early computers lacked any form of operating system. The user had sole use of the machine and would arrive armed with program and data, often on punched paper and tape. The program would be loaded into the machine, and the machine would be set to work until the program completed or crashed. As machines became more powerful, the time needed for a run of a program diminished and the time to hand off the equipment became very large by comparison. Accounting for and paying for machine usage moved on from checking the wall clock to automatic logging by the computer. Run queues evolved from a literal queue of people at the door, to a heap of media on a jobs-waiting table, or batches of punch-cards stacked one on top of the other in the reader, until the machine itself was able to select and sequence which magnetic tape drives were online. Where program developers had originally had access to run their own jobs on the machine, they were supplanted by dedicated machine operators who looked after the well-being and maintenance of the machine and were less and less concerned with implementing tasks manually. When commercially available computer centers were faced with the implications of data lost through tampering or operational errors, equipment vendors were put under pressure to enhance the runtime libraries to prevent misuse of system resources. Automated monitoring was needed not just for CPU usage but for counting pages printed, cards punched, cards read, disk storage used and for signaling when operator intervention was required by jobs such as changing magnetic tapes.

All these features were building up towards the repertoire of a fully capable operating system. The true descendant of the early operating systems is what is now called the "kernel". In technical and development circles the old restricted sense of an OS persists because of the continued active development of embedded operating systems for all kinds of devices with a data-processing component, from hand-held gadgets up to industrial robots and real-time control-systems, which do not run user-applications at the front-end. An embedded OS in a device today is not so far removed as one might think from its ancestor of the 1950s.

The Mainframe Era

Early operating systems were very diverse, with each vendor or customer producing one or more operating systems specific to their particular mainframe computer. Every operating system, even from the same vendor, could have radically different models of commands, operating procedures.

The state of affairs continued until the 1960s when IBM, already a leading hardware vendor, stopped the work on existing systems, and put all the effort into developing the System/360 series of machines, all of which used the same instruction architecture. IBM intended to develop also a single operating system for the new hardware, the OS/360. However as the performance differences across the hardware range and delays with software development, a whole family of operating systems were introduced instead of a single OS/360. The best part is that IBM maintained full compatibility with the past, so that programs developed in the sixties can still run under z/VSE (if developed for DOS/360) or z/OS (if developed for OS/MFT or OS/MVT) with no change.

Minicomputers and the rise of UNIX

The beginnings of the UNIX operating system was developed at AT&T Bell Laboratories in the late 1960s. Because it was essentially free in early editions, easily obtainable, and easily modified, it achieved wide acceptance. It also became a requirement within the Bell systems operating companies. Since it was written in a high level C language, when that language was ported to a new machine architecture UNIX was also able to be ported. This portability permitted it to become the choice for a second generation of minicomputers and the first generation of workstations. By widespread use it exemplified the idea of an operating system that was conceptually the same across various hardware platforms. information.

The Personal Computer Era

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, often loaded from ROM and known as Monitors. One notable early disk-based operating system was CP/M, which was supported on many early microcomputers and was closely imitated in 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. In the 80's Apple Computer Inc. (now Apple Inc.) abandoned its popular Apple II series of microcomputers to introduce the Apple Macintosh computer with the an innovative Graphical User Interface (GUI) to the Mac OS.

The introduction of the Intel 80386 CPU chip with 32-bit architecture and paging capabilities, provided personal computers with the ability to run multitasking operating systems like those of earlier minicomputers and mainframes. Microsoft's responded to this progress by hiring Dave Cutler, who had developed the VMS operating system for Digital Equipment Corporation. He lead the development of the Windows NT operating system, which continues to serve as the basis for Microsoft's operating systems line. Steve Jobs, a co-founder of Apple Inc., started NeXT Computer Inc., which developed the Unix-like NEXTSTEP operating system. NEXTSTEP would later be acquired by Apple Inc. and used, along with code from FreeBSD as the core of Mac OS X.

Minix, an academic teaching tool which could be run on early PCs, would inspire another reimplementation of Unix, called Linux. Started by computer student Linus Torvalds with cooperation from volunteers over the internet, developed a kernel which was combined with the tools from the GNU Project.

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