Cs 490 test 1

Interrupt

a mechanism by which other modules (I/O, memory) may interrupt the normal sequencing of the processor. The process checks for an interrupt flag at the end of each fetch-execute cycle to determine if something needs to be dealt with.

difference between a multiprocessor and a multicore system

A multicore computer is a special case of a multiprocessor, in which all of the processors are on a single chip.

Multiprocessing

a mode of operation that provides for the physical computation of processes in parallel, on different CPUs/computing hardware

I/o bound

Process spends more time waiting for i/o instead of computing instructions on alu/cpu

CPU bound

Process spends more time computing instructions than waiting for i/o

Multiprogramming

a mode of operation that provides for the interleaved execution of two or more computer programs by a single processor

Scheduling

Most installations used a hard copy sign up sheet to reserve computer time

kernel

a portion of the operating system that includes the most heavily used portions of software

difference between a monolithic kernel and a microkernel design

Microkernels implement the most important core features in the memory resident portion of the operating system where Monolithic kernels include all possible OS features in the core. Microkernels use memory more efficiently by allowing some operating system features to be managed as if they were normal processes and can be swapped in/out of memory.

Process

Supports goal of an operating system as a resource manager

Comprised of:

• a program in execution

• Associated data in memory

• Process control block (Created and managed by os software)

5 state model

1) running - process currently being executed

2) ready - process is ready to execute

3) blocked - process can’t resume execution until some event occurs

4) new - process just created, not yet loaded into memory

5) exit - process is completed and its pcb storage can be reclaimed

7 state model

Adds ready/suspend and blocked/suspend to 5 state model

State transitions

Admit, event complete, dispatch, time out, event wait, release

Multithreading

In this process an environment contains a virtual memory address space that holds the process image and protected access to processors, communication, files, and other resources

Single threaded vs multi threaded processes

User level threads

All details of thread management are performed by the application itself via thread libraries

Kernel level threads

The operating system can map many user level threads into some subset of kernel level

Mutual exclusion

a program object that prevents multiple threads from accessing the same shared resource simultaneously

Dekkers algorithm

A solution to mutual exclusion. works to enforce mutual exclusion without locking the processes

Atomic actions

Multiple actions on a memory location completes within a single instruction cycle

Multiple applications

multiprogramming was invented to handle this, and allow processing time to be shared among multiple active applications

Structured applications

modular design sometimes encompasses developing problem solutions built from multiple concurrent processes

Operating system structure

OS services can be developed as a set of concurrent processes

Semaphore

A special variable type with an integer value. Used with shared memory systems, processes can each utilize the shared semaphores

Binary semaphores

Semaphores that start with 1

Counting semaphores

Semaphores that start with >= 1

SemWait

Decrements the value as an atomic action

SemSignal

Semaphore value is incremented

Monitor

Controls the shared data. Provides types of locks using condition variables or condition flags

positives of semaphore

Allows more than one thread to access critical regions. Flexible resource management. Machine independent.

Negatives of semaphores

a primitive tool, and may be scattered throughout the code, requiring programmers to be disciplined at verifying the correctness of the combined operations

Condition variables

Manages synchronization. Cannot be scattered in code

Producer/consumer problem

Common buffer/sync problem. Need to ensure that a producer doesn’t try to add to a full buffer and that a consumer doesn’t try to take from an empty buffer.

Reader/writer problem

A data area is shared among many processes. Some processes only read the data area, (readers) and some only write to the data area (writers)

Conditions that must be satisfied:

•Any number of readers may simultaneously read the file

•Only one writer at a time may write to the file

•If a writer is writing to the file, no reader may read it

variations include reader priority (writers starve)

Deadlock

the permanent blocking of a set of processes that compete for system resources or communicate with each other

Starvation

A process or resource is unable to make progress or access a resource it needs due to allocation of resources to other processes or tasks

4 conditions for deadlock to occur

Mutual exclusion, hold & wait, no preemption, circular wait

Uniprocessor

Only one process can run at a time, and to run another one you’d have to wait until the current one is finished.