340 Final

Von Neumann architecture

Computer structure where instructions and data are stored in the same main memory.

Operating system

Software that manages hardware, provides services for programs, and acts as intermediary between user and hardware.

Kernel

The one program always running in memory that controls the system.

Control program

Program that manages execution of user programs and controls I/O devices.

CPU

Hardware component that executes instructions.

Processor

Physical chip containing one or more CPUs.

Core

Basic computational unit within a CPU.

Multiprocessor system

System with two or more processors or cores sharing resources.

Multicore processor

Single CPU chip with multiple processing cores.

Parallelization

Dividing a program into components that run in parallel.

Trap

Software-generated interrupt caused by error or system-call request.

Interrupt

Hardware mechanism that signals the CPU for attention.

Interrupt vector

Kernel structure containing addresses of interrupt handlers.

System call

Software-triggered interrupt used by a process to request OS service.

Multiprogramming

Technique of keeping multiple jobs in memory to maximize CPU utilization.

Multitasking

Switching CPU between jobs so users can interact with processes.

Degree of multiprogramming

Number of processes in memory.

Process

A program in execution.

CPU scheduler

Kernel routine selecting next ready thread/process for execution.

CPU-bound process

Spends more time computing than performing I/O.

I/O-bound process

Spends more time performing I/O than computing.

CPU burst

Period when process executes on CPU.

I/O burst

Period when process waits for I/O.

Virtual memory

Technique allowing execution of process not fully in physical memory.

Logical memory

Memory as viewed by user.

User mode

Restricted CPU mode preventing privileged instructions.

Kernel mode

CPU mode allowing execution of privileged instructions.

Program counter

Register containing address of next instruction.

Cache

Fast temporary storage improving memory performance.

Cache coherency

Ensuring consistent copies of data across multiple caches.

Cache-consistency problem

Challenge of maintaining identical cached data.

Caching

Using temporary storage to improve access speed.

Process states

New, Ready, Running, Waiting, Terminated.

New state

Process being created and not yet admitted for execution.

Ready state

Process waiting in Memory for CPU.

Running state

Process executing instructions on CPU.

Waiting state

Process waiting for event or I/O completion.

Terminated state

Process finished execution.

Text section

Executable code portion of process memory.

Data section

Global variables of process.

Heap

Dynamically allocated memory.

Stack

Temporary storage for function calls and local variables.

Activation record

Stack frame containing parameters, return address, locals.

Process Control Block (PCB)

OS data structure representing a process and stores all the info about the process.

What does the PCB process state hold

Current state of process.

What does the PCB program counter hold

Address of next instruction.

What do the PCB CPU registers hold

Saved register contents.

What does the PCB scheduling information hold

Priority and queue pointers.

What does the PCB memory-management information hold

Base/limit registers or page table info.

What does the PCB accounting information hold

CPU time used, job number.

What does the PCB I/O status information hold

Open files and allocated devices.

Context switch

Saving current process state and restoring another.

Context-switch time

Overhead time where no useful work is done.

Independent process

Does not share data with others.

Cooperating process

Can affect or be affected by other processes.

Interprocess communication (IPC)

Mechanism allowing processes to exchange data.

Shared memory

IPC model where processes share memory region.

Message passing

IPC model where processes exchange messages.

Producer-consumer problem

Classic example of synchronization using shared buffer.

Empty buffer condition

in == out.

Full buffer condition

(in + 1) % BUFFER_SIZE == out.

Pipe

Communication conduit between processes.

fork()

Creates new process copy of calling process.

fork() return values

0 in child, child PID in parent, -1 on failure.

open()

Opens file and returns file descriptor.

O_RDONLY

Open file for reading only.

O_WRONLY

Open file for writing only.

O_RDWR

Open file for both reading and writing.

O_CREAT

Create file if not exists.

O_TRUNC

Truncate file to length 0.

O_APPEND

Append writes to end of file.

read()

Reads bytes from file descriptor.

write()

Writes bytes to file descriptor.

close()

Closes file descriptor.

wait()

Parent waits for child process to finish.

Thread

Basic unit of CPU utilization consisting of thread ID, program counter, register set, and stack.

Multithreaded process

A process containing multiple threads sharing code, data, and resources.

Responsiveness benefit

Multithreading allows application to remain responsive while part is blocked.

Resource sharing benefit

Threads share memory and OS resources by default within same process.

Economy benefit

Thread creation and context switching are cheaper than processes.

Scalability benefit

Threads can run in parallel on multicore systems.

Multicore system

System with multiple cores appearing as separate CPUs.

Concurrency

System supports more than one task making progress.

Parallelism

System performs more than one task simultaneously.

Concurrency without parallelism

Possible on single-core systems via context switching.

Data parallelism

Distributing subsets of same data across cores performing identical operations.

Task parallelism

Distributing different tasks across cores.

Pthreads

POSIX thread standard defining API for thread creation and synchronization.

pthread_t

Data type for thread identifier.

pthread_create()

Creates new thread; takes pointer to thread ID, attributes, function pointer, and argument.

pthread_join()

Waits for specified thread to terminate.

pthread_self()

Returns ID of currently executing thread.

CPU scheduling

Process of selecting which ready process runs next.

Multiprogramming objective

Keep CPU busy at all times.

CPU–I/O burst cycle

Process alternates between CPU bursts and I/O bursts.

Ready queue

Queue of processes waiting for CPU.

Preemptive scheduling

OS may interrupt running process.

Nonpreemptive scheduling

Running process keeps CPU until it blocks or terminates.

What are the Scheduling criteria?

CPU utilization, throughput, turnaround time, waiting time, response time.

CPU utilization

Percentage of time CPU is busy.