CPSC 251 Fall 2001 – Examination #1

Name: ______KEY_______________________________________________

Answer five (5) problems as fully as possible for full credit. Points will be lost if no working is given (where necessary).

1. (20 pts) Define the following terms as fully as possible.

(i) Multiprogramming - – to increase CPU utilization by organizing jobs in memory into queues such that the CPU is always busy

(ii) Multiprocessing – job execution involving more than one processor with close communication.

(iii) Time-sharing – extension of multiprogramming by CPU executing multiple jobs switching between them frequently.

(iv) Spooling- buffering jobs (usually output) for a device like a printer.

(v) Batch - putting jobs with similar interests together before they are submitted.

2. ( 20 pts) (a) List five operating systems in use today – that you are aware of. How many of these have you used? Windows 9x, me, NT, Solaris, BeOS, MacOS-x, OS/2

______________________________________________________________ _______

(b) What is a virtual machine? - When an OS, using CPU scheduling and MM, creates an illusion that each process in the system has its own machine.

© How does it work? - The OS uses CPU scheduling and memory allocation and for each allocated process creates an illusion that it has its own system resources – i.e. cpu, memory, etc..

3. (20 pts) (a) What are two differences between user-level threads and kernel-level threads? Under what circumstances is one type better than the other? –

(i) Kernel threads are slower – because their management is done by the kernel.

(ii) In a multiprocessor environment, multiple threads can be scheduled on more than one processor.

(b) Describe the differences among the following schedulers:

(i) short-term - selects jobs in the ready queue and allocates them CPU.

(ii) medium-term – selects jobs and removes them from MM – reduces degree of multiprogramming.

(iii) long-term - selects jobs from a mass-storage like a disk and allocates them to MM.

4. (20 pts) (a) Describe the actions taken by a kernel to context switch between processes - During context-switch the kernel saves the context of process (cpu registers, pc, open files, etc..)

(b) What is the purpose of a system call? – to allow a process in the user mode gain access to the kernel resources like privileged instructions – i.e. I/O instructions.

© What is a DMA? For what types of operations is DMA useful? –DMA is a direct memory access – when I/O devices without CPU intervention takes large blocks of data directly to MM. For massive data movement between MM and devices.

5. (20 pts) (a) In a multiprogramming and time-sharing environment, several users share the system simultaneously. This can result in several security problems.

(i) What two such problems? – corruption of data/instruction, - overwrite of each other’s address space. –

( ii) Can we ensure the same degree of security in a time-shared machine as we have in a dedicated machine? Explain! – Probably not!

(b) Describe the differences between symmetric and asymmetric multiprocessing . What are three advantages of multiprocessor system? – In symmetric multiprocessing the processors sometimes share a CPU clock and expanded global memory. Also they share an identical copy of the OS.

- In asymmetric multiprocessing, the processors have independent CPU clocks and do not share OS and have limited global memory.