What Is An Operating System

Many definitions can be given for an Operating System; but in the end all end up at the same point.

• "Operating System" is a set of software which controls and monitors a computer's resources to enable the users and programmers to use these resources easily and effectively.
• An Operating System is a program which interacts directly with the hardware to provide an interface to other system software and application software whenever a system resource is needed.
• Operating Systems hide the details of hardware of a computer hence making life easier to the programmer and user.
• Operating Systems are programs that organize sharing of computer systems' resources among users and application programs.

Operating Systems consist of a large set of software modules, which take care of the (usually hard to use) system hardware and hide the technical details from the programmer and user. As example we can mention hard disks. As you know hard disks are magnetic plates rotating in a closed case and the proper procedure of reading/writing to a hard disk must do the following tests before attempting to read/write to the disk:

• Is there really a disk connected to the computer?
• Is(are) the disk plate(s) rotating?
• If yes, are they rotating at the correct speed?
• Are the read/write heads on the correct track?
• Is the sector to be read or written under the read/write head?
• Was reading/writing successfull?

These details are much more complicated then the way they are described above. If every programmer needed to go into these details to write useful programs it would take 10 years to train a programmer and much longer to develop reasonable application programs.

The modules of the operating system takes care of all these complex procedures when a programmer needs to wite code to write records in a file or read them.

Operating systems also take care of user requests when they need to access system resources.

Computer System Resources

The following are the major resources of a typical digital computer system:

• The central processing unit (CPU),
• Primary Memory (RAM),
• Secondary Memory units like hard disks, floppy disk drives,
• Keyboard,
• Display units,
• Programs installed on the computer,
• Networking facilities of the computer like Ethernet interface,
• Printer, scanner, mouse
• Time,
• etc. etc..

Some resources can be allocated to a single user at a time (like the keyboard), whereas some resources can be shared among the users; such as the strorage space on disk drives.

One of the main duties of an operating system to make arrangements for users to share resources. An example is the file system on disks. The operating system organizes the storage areas on a disk so that different users can store their data/programs in separate parts of the disks. Files and directories are the main tools of an OpSys to enable disk sharing.

Another typical example for resource sharing is the sharing of "time" among users in a "multi-user" computer system where more than one user runs programs at a given time. "Tme" ia managed by the opsys so that it seems to the users that they are using the computer system only themselves; minimizing the slowing effect of other users.