Operating Systems

1. Feeding
2. Chambering
3. Locking
4. Firing
5. Unlocking
6. Extract ing
7. Ejecting
8. Cocking

(FM 3-23.35 June 2003 / 1-13 / PDF 17)

An operating system is a generic term for software that interfaces and buffers between the users and user application programs and the computer hardware which includes memory, disk drives, etc.

It can be as simple as the old(er) named Disk Operating System (MSDOS, PCDOS, DRDOS, DOS-11, DOS/360, etc) and Tape operating system (TOS) which had no restrictions on what a running program could do but loaded programs into memory, start them, and did respond to requests by programs for system functions such as finding, reading and writing files.

It can be as complex as a multiuser, multiprogramming, multiprocessing system where it manages memory, CPU(s), device assignment, security, communications and other functions as in Z/OS. IBM I, OpenVMS, Unix implementations, Linux, or Windows.

It is software. You can install and uninstall operating systems as you like, without changing any hardware inside your computer.

The operating system is the system your using such as Microsoft's Windows versions (Windows XP, Windows vista, Windows 7, etc.), Apples Mac OS X snow leopard, Linux distributions.

The OS is a system software which provides services for application software. The OS controls Hardware and software like MS word, Photoshop and wordpad.

It is the software of your system that allows you to do pretty much everything. Run programs, go onto the Internet or even look at pictures.

The Operating system is a software consisting of programs and data that runs on computers and manages the hardware resources and also provides a platform for various application software.

An operative system is software serving as a foundation for processes on your computer. The operating system undertakes memory management and important security and stability enhancing tasks that is required for other software to run correctly. Computer hardware often differ in design and function and part of the operative systems's job is to minimize the design work needed by the other layers software to support each type of hardware.

this is my doubt about the non-preemptive priority scheduling. i m doing bachelor of engineering in IT and this question in end semester exam. the question is as follows:

Assume you have the following jobs to be executed with one processor, with the jobs arriving in the order listed here:

Process Burst Time Priority

P1 80 5

P2 20 1

P3 10 3

P4 20 2

P5 50 4

Suppose the system uses priority scheduling. Draw Gantt chart and calculate average waiting time for the processes.

My doubt is:

suppose if we were to use non-preemptive priority scheduling, the question says the jobs arriving in the order listed, so as per the order P1 will arrive first so it will get the CPU first and in non-preemptive once a job gets CPU it will not leave CPU till the process finishes, then as per the order P2 will come and same thing repeats.... so it acts like FCFS scheduling and priority is of no use here. But my lecturer says we have to follow the priority and P2 will come first, but the line the jobs arriving in the order listed is still not letting me agree with my lecturer. Can anyone help out?

SPECIAL REQUIRMENTS OF A MULTIPROGRAMMING OS:-

(A)I/O interrupts and DMA.

=>In order to execute instructions while I/O device is busy.

(B)MEMORY management.

=>Several ready-to-run jobs must be kept in memory.So we need more memory size.

(C)MEMORY protection.

=>data and programs

A multiprogramming system requires:

• A CPU (central processing unit) supporting a user mode for application processes and a system mode which can execute privileged instructions that control devices, memory management and other parts of the hardware. It can be called system mode, privilege mode, supervisor mode or kernel mode and it is possible to have more than one of these to allow different levels of system control. Application programs requesting reads, writes and other privileged functions pass the request to the system which in system mode would verify the validity of the request, executes the request if possible or queues the request to be done later and selects a different process to run.
• DMA (direct memory access) hardware to allow fast data transfers independent of program execution.
• A Clock/timer with interrupt capability allowing system software to manage time allocation of application programs and to pause them to allow other programs to run.
• I/O device interrupt structure to interrupt running programs so that the system can process I/O device completion and other requests and then return control to the running program.
• Memory mapping hardware to give running processes there own memory address area.
• Memory protection to prevent a running program from violating the integrity of other applications already in memory and to determine when a running process is using a memory address that has been swapped out so it can be brought back in.