Midterm Terms Flashcards
Process Control Block
data package that contains register contetns, values of all variables, state of any I/O, pointers to all open files, any interruptes, the program in memory, the program counter
Time quanta
The period of time a process is allowed to run uninterrupted
Context Switching
The switching of the CPU from one process to another
Turn Around Time
Completion time - arrival time
Multilevel queue
A scheduling algorithm that gives preference to short jobs, I/O processes, and separates processe sinto categories based on the need of the processor
Deadlock
A problem occuring when resources for Job A to occur are competing with Job B. B cannot start until A finishes.
Preemptive multitasking
A multitasking method that shares processing time with all running programs.
Process/Resource diagram
R1, P1, R2, P2, R3, P3
Recovery Algorithm
Identify the victim process, the one with the lowest priority and pull the process out of the key so its resources are available
Volume
A single accessible storage area with a single file system
Volume descriptor
Describes the characteristics of the file system information present on a given CD-ROM or volume.
Master File Directory
An essential data structure on any ITS file system, one level of directories instead of hierarchial.
Block
A portion of allocated memory.
Single User System
Only one program can be run at a time.
Fixed Partitions
The OS has a job scheduler. It keeps track of incoming jobs and which partitions are free, and if there is enough space for a program to fit.
Dynamic partitions
Good at assigning space for initialprograms, but suffer from external fragmentation over time
Relocatable Dynamic Partitions
Dynamic partitions that the operating system can move around to free up space for a new process in the queue.
Kernel
Responsible for resource allocation, low-level hardware interfaces, security.
Compaction
Moves all the allocated blocks to one end of memory (defragmentation)
Page
Small, fixed sized blocks of virtual memory.
Page Frame
Just like a page but in physical memory, not logical memory
Demand Paging
A page is not loaded until it is referenced by a process
Program Counter
A processor register that indicates where a computer is in its program sequence
Page Fault
Occurs when the kernel needs a page, finds it doesn’t exist in physical memory because it has been paged-out, and re-reads it in from disk
Page Replacement Policy
The steps carried out by the operating system when a page fault occurs
Segment
Are user defined logical modules in a program.
Segmentation Fault
An error in which a running Unix program attempts to access memory not allocated to it and terminates with a segmentation violation error and usually a core dump.
Pipe
A form of redirection to send the output of one program to another program for further processing
Symbolic Link
A file that links to another file.
External Fragmentation
When free memory is separated into small blocks and is interspersed by allocated memory
Internal Fragmentation
A partition is split to hold more jobs
Memory Map Table
Keeps track of which page frames are free.
Process
An instance of a program in execution
Process scheduling algorithms
FIFO, Shortest Job First, Priority, Round Robin, Multilevel queue
Redirection
In Unix, to send output from a process to a different file or device.
Round Robin
Process scheduling algorithm
Virtual Memory
Using a disk as an extension of RAM
CPU Bound Processes (in multilevel queues)
When the time for a task to complete is determined principally by the speed of the CPU
I/O Bound Processes
When the time it takes to complete a computation is determined principally by the period spent waiting for I/O operations to be completed.
