Operating Systems

Editor's Notes

• #5: The structure of OS consists of 4 layers:1)Hardware Hardware consists of CPU, Main memory, I/O Devices, etc,2)Software (Operating System) Software includes process management routines, memory management routines, I/O control routines, file management routines3)System programs This layer consists of compilers, Assemblers, linker etc.4)Application programs This is dependent on users need. Ex. Railway reservation system, Bank database management etc.,
• #6: 1)Batch systemsBatch operating systems were designed in the 1950s to control mainframe computers.At that time, computers were large machines that used punched cards for input, line printers for output and tape drives for secondary storage media.Each program to be executed was called a job.A programmer who wished to execute a job sends a request to the operating system.2) Time-sharing SystemsMultiprogramming brought the idea of time sharing: resources could be shared between different jobs, with each job being allocated a portion of time to usea resource.Because a computer is much faster than a human, time sharing is hidden from the user—each user has the impression that the whole system is serving them exclusively3) Personal SystemsWhen personal computers were introduced, there was a need for an operating system for this new type of computer.During this era, single-user operating systems such as DOS (Disk Operating System) were introduced.4) Parallel SystemsThe need for more speed and efficiency led to the design of parallel systemsmultiple CPUs on the same machine.Each CPU can be used to serve one program or a part of a program, which means that many tasks can be accomplished in parallel instead of serially.The operating systems required for this are more complex than those that support single CPUs.5) Distributed systemsNetworking and internetworking have created a new dimension in operating systems.A job that was previously done on one computer can now be shared between computers that may be thousands of miles apart.Distributed systems combine features of the previous generation with new duties such as controlling security.6) Real-time SystemsA real-time system is expected to do a task within a specific time constraint.They are used with real-time applications, which monitor, respond to or control external processes or environments.
• #10: 1) Processor Management: It means assigning processor to different tasks which has to be performed by the computer system.2) Memory Management: It means allocation of main memory and secondary storage areas to the system programmes, as well as user programmes and data.3) Input and Output Management: It means co-ordination and assignment of the different output and input devices while one or more programmes are being executed.4) File System Management: Operating system is also responsible for maintenance of a file system, in which the users are allowed to create, delete and move files.5) Establishment and Enforcement of a Priority System: It means the operating system determines and maintains the order in which jobs are to be executed in the computer system.Assignment of system resources, both software and hardware to the various users of the system.
• #11: The first two responsibilities address the need for managing the computer hardware and the application programs that use the hardware.The third responsibility focuses on providing an interface between application software and hardware so that application software can be efficiently developed.Since the operating system is already responsible for managing the hardware, it should provide a programming interface for application developers.
• #12: 1) Real-time Operating System: RTOS) - Real-time operating systems are used to control machinery, scientific instruments and industrial systems.An RTOS typically has very little user-interface capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use.A very important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time, every time it occurs.2)Single-user, single task Operating Systems: As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.3)Single-user, multi-tasking Operating Systems: this is the type of operating system most people use on their desktop and laptop computers today. Microsoft's Windows and Apple's MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time. For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.4) Multi-user - A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems