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Operating Systems

Operating Systems. Overview. What is an Operating System (OS) What Operating Systems do. Operating system issues Kinds of Operating Systems. What is an OS?.

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Operating Systems

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  1. Operating Systems

  2. Overview • What is an Operating System (OS) • What Operating Systems do. • Operating system issues • Kinds of Operating Systems

  3. What is an OS? “An operating system is a layer of software which takes care of technical aspects of a computer's operation. It shields the user of the machine from the low-level details of the machine's operation and provides frequently needed facilities” Taken from http://www.iu.hio.no

  4. What is an OS? • An Operating System makes the computing power available to users by controlling the hardware • Without an OS, computers would only be able to run one program at a time • Programs must run according to the rules of the OS

  5. What Operating Systems do: • Provide software for driving the hardware of the computer • Implement a file system which provides a way of organizing files logically • Distribute computer resources between applications

  6. 1. Software that Runs Hardware • A driver is software that designed to run a piece of hardware • Ex: Printer, fancy keyboard, scanner • New drivers are built into the OS. This is why it is often necessary to restart your computer when a driver is added

  7. 2. File System • The OS must save files in a logical efficient way • Hard drive, floppy disk • Through FAT (File Allocation Table) • Recall, FAT32 vs FAT16 • 32 bit addressing means each section of memory is broken up into 2^32 individual addressing locations • Much faster to find a file!

  8. File Systems: NTFS • NTFS is the “NT File System” developed by Microsoft • Faster and more efficient. • XP and Vista would use NTFS

  9. RAM • OS is also responsible for memory allocation in RAM • The OS itself stays in RAM while the computer is on • OS controls what is moved into and out of RAM

  10. Virtual Memory • Several programs can’t fit in main memory so what happens? • Virtual memory is parts of active programs stored on the hard drive. • EX: I’ve got Windows XP running, MS Word, 3 Explorer Windows one being active • Rather then not letting you open more programs the OS will run them using Virtual Memory

  11. 3. Distributing Computer Resources • The CPU can only do one thing at a time. Fortunately it can do billions of things per second… • The OS is responsible for giving CPU time to currently running applications. • The OS also makes sure two applications don’t try accessing the same piece of hardware at the same time.

  12. 2 OS Issues • Concurrency control (multi-tasking) • Deadlock

  13. Concurrency Control • Several programs running at a time • Means Sharing CPU time • While a program waits for an I/O operation another program can use the CPU

  14. Deadlock • Program A wants to copy from disk1 to disk2 and takes control of disk1 • Program B wants to copy from disk2 to disk1 and takes control of disk2 • Program A must wait until program B releases disk2 and program B must wait until program A releases disk1 • Programs A and B will wait forever!

  15. Deadlock Prevention • OS must have a systematic way of controlling program execution • This is a very complex problem • One simple not very efficient solution is to have programs “timeout”, in our example program A would timeout first and release disk 1 and try again shortly

  16. Kinds of Operating Systems • What’s the best? • Windows=Microsoft =monopoly!!! • Success due to??? • Other alternatives: • Mac- I’ve never met a sad Mac user • Linux/Unix- Small very efficient, maybe less intuitive

  17. Work on OS Assignment

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