Uh, What's an Operating System?

For a computer to do anything useful, it needs both application software (programs you use) and an operating system (programs the computer uses). The operating system sits between the physical hardware that makes up a computer (the monitor, keyboard, CPU, hard drive, and so forth) and the end-user software that people use to process documents, play games, and all that good stuff.

My brother Tom and I are both into computers. We're computer programmers by trade, but I'm quick to point out that we produce very different kinds of software. The difference, as I like to explain it, is this: I write software for people (application software), and Tom writes software for computers (operating system software).

We commonly think of the CPU as the brain of a computer, but in reality, it can't do much besides crunch numbers and move data around in the computer's memory. The job of the operating system (OS) is twofold:

• To work with computer hardware to process user requests by
  • interpreting keystrokes from the keyboard,
  • displaying text and images on the screen,
  • storing files on the hard disk,
  • sending documents to a printer,
  • communicating over a modem.
• To manage the application software's use of memory (RAM) and processor time.

If you've used a multitasking environment like Windows or a multiuser mainframe system, you've seen the concept of "time-slicing" in action. While your computer has only one CPU, which can do only one thing at a time, the OS can make it seem like several people or programs are using the CPU simultaneously. Similarly, even though the real memory (RAM) is shared by all running applications, the OS can make it seem like you have it all at your disposal, all the time, by sharing it between applications--using a technique called paging.

The OS time-slices by giving one user or application exclusive use of the hardware for a brief instant, and then doing the same for the next user or application. On systems with adequate horsepower, this approach works so that you never even know about that little game of round-robin going on behind the scenes. On a wimpy computer or a mainframe with too many users, it's toe-tappin' time for everybody.

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Comments - most recent first (Please feel free to answer questions posted by others!) Jim     (18 Feb 2012, 18:01) Bob...I like your site, as it is very informative and actually gives examples of the sometimes cryptic command line sequences. I suspect you and I are alike in one regard, we likely both very much dislike having typos and/or grammatical errors in our publications. In that regard, I suspect that in your mind at least, you intended the following to have the inserted ALL CAPS word in the sentence. I read it twice with my mind supplying the missing word for me before I realized the word was actually NOT there. "On systems with adequate horsepower, this approach works so WELL that you never even know about that little game of round-robin going on behind the scenes." No need to post this comment, just trying to be helpful! Best Regards, Jim Bob Rankin     (06 Jan 2012, 10:48) @abdiwahab muhumed - Done. Start here: //lowfatlinux.com abdiwahab muhumed     (06 Jan 2012, 03:51) i have some point from maintenance of computer but what i want from you is that to facilitate me every thing you can do starting for the frist step to the last so dear of mine would you please help me deepanjan ghosh     (15 Oct 2011, 12:42) great material dr bob....thanks for sharing and keep up the good work!!!!! cheers! Clement Koromije     (29 Apr 2011, 13:20) Hi Dr Bob, I'm sending you this e-mail all the way from Tanzania in East Africa. I just want you to know that your lessons are invaluable to some of us who don't have access to computer learning institutions. I hope that by the end of your course I'll at least have a quarter of your knowledge. Thanks so much for your kind generosity in sharing this valuable information with us. Regards, Clement disha     (20 Feb 2011, 01:16) dis 1 is really hlpful.... i m reallly thanful to 1 f ma frn who got me kno bout ds.... thanks a lot sapiii :-) n m grt thankful to dr bob for giving us a helping hand thanks a lot sr :-) devang     (12 Feb 2011, 06:43) i like the linux Flashwente     (07 Feb 2011, 15:50) I will use this course to advance my career. If I make my millions, I will try to pay it forward. You are a saint, Bob. S.Sivarama Sarma     (02 Oct 2010, 00:55) Dear Bob It is just fantastic for putting useful material in the web. Thanking you very much for guiding us. Siva Rajesh     (19 Apr 2010, 02:17) Hi Ujjal, I think u r confused with installing packages in ubundu. Each packages to be installed in different ways according to the package type u have. so let me know the s/w you looking for. for assistance u can look in ubuntuforums.org r mail me at stripling20 at gmail dot com Ujjal     (19 Apr 2010, 01:08) I was using xp.but now i have installed ubuntu.i am very much confused about the commands of linux. I cant install anything.please help me. bashir ahmed - islamabad Pakistan     (25 Feb 2010, 20:10) First of all THANK U VERY MUCH for writing an helpful and useful tutorial on Linux in simple and consolidated form. I m a new user and try to learn the LINUX on the advice of my Teacher when i m attending the two weeks networking class in windows operating. I have recently finished the linux course with servers only in 3 weeks. Now i m trying to revise and also in detail about the commands and step by step. Actually i m doing part time job as teacher in academy in the field of computer. Now my students are emphasis to teach them linux. So i am looking and searching on net, but i cannot found the crash program type contents of the linux. Today during searching i found this site which is really helpful. If kindly u or any honourable member give the guide line or valuable advice for further improvement and teaching. I shall be grateful for all of them. with best regards and wishes bashir ahmed Rajesh     (07 Feb 2010, 22:00) @vilas, The main diff btw windows & linux are 1.) Linux is an open source development model and so the programmer can redesign the OS but its not in windows 2.) The linux servers have surpassed windows server OS in security. vilas hade     (06 Feb 2010, 10:25) what is different beetwin linux & windows I welcome your comments. However... I am puzzled by many people who say "Please send me the Linux tutorial." This website *is* your Linux Tutorial! Read everything here, learn all you can, ask questions if you like. But don't ask me to send what you already have. :-) NO SPAM! If you post garbage, it will be deleted, and you will be banned. *Name: Email: Notify me about new comments on this page Hide my email *Text:

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