16.01 - Purposes of an Operating System (OS) Flashcards
Bootstrap
A small program that is used to load other programs to “start up” a computer
Scheduling
Process manager which handles the removal of running programs from the CPU and the selection of new processes
Direct memory access (DMA) controller
Device that allows certain hardware to access RAM independently of the CPU
Kernel
The core of an OS with control over process management, memory management, interrupt handling, device management, and I/O operations
Multi-tasking
Function allowing a computer to process more than one task/process at a time
Process
A program that has started to be executed
Pre-emptive
Type of scheduling in which a process switches from running state to steady state or from waiting state to steady state
Quantum
A fixed time slice allocated to a process
Non-preemptive
Type of scheduling in which a process terminates or switches from a running state to a waiting state
Burst time
The time when a process has control of the CPU
Starve
To constantly deprive a process of the necessary resources to carry out a task/process
Low-level scheduling
Method by which a system assigns a processor to a task or process based on the priority level
Process control block (PCB)
Data structure which contains all the data needed for a process to run
Process states
Running, ready, and blocked; the states of a process requiring execution
Round robin (scheduling)
Scheduling algorithm that uses time slices assigned to each process in a job queue
Context switching
Procedure by which, when the next process takes control of the CPU, its previous state is reinstated or restored
Interrupt dispatch table (IDT)
Data structure used to implement an interrupt vector table
Interrupt priority levels (IPL)
Values given to interrupts based on values 0 to 31
Optimisation (memory management)
Function of memory management deciding which processes should be in main memory and where they should be stored
Paging
Form of memory management which divides up physical memory and logical memory into fixed-size memory blocks
Physical memory
Main/primary RAM memory
Logical memory
The address space that an OS perceives to be main storage
Frames
Fixed-size physical memory blocks
Pages
Fixed-size logical memory blocks
Page table
Table that maps logical addresses to physical addresses; it contains page number, flag status, frame address, and time of entry
Dirty
Term used to describe a page in memory that has been modified
Translation lookaside buffer (TLB)
This is a memory cache which can reduce the time taken to access a user memory location; it is part of the memory management unit
Segments memory
Variable-size memory blocks into which logical memory is split up
Segment number
Index number of a segment
Segment map table
Table containing the segment number, segment size, and corresponding memory location in physical memory: it maps logical memory segments to physical memory
Virtual memory
Type of paging that gives the illusion of unlimited memory being available
Swap space
Space on HDD used in virtual memory, which saves process data
In demand paging
A form of data swapping where pages of data are not copied from HDD/SSD into RAM until they are actually required
Disk thrashing
Problem resulting from use of virtual memory. Excessive swapping in and out of virtual memory leads to a high rate of hard disk read/write movements, thus reducing processing speed
Thrash point
Point at which the execution of a process comes to a halt since the system is busier paging in/out of memory rather than actually executing them
Page replacement
Occurs when a requested page is not in memory and a free page cannot be used to satisfy allocation
Page fault
Occurs when a new page is referred but is not yet in memory
First in first out (FIFO) page replacement
Page replacement that keeps track of all pages in memory using a queue structure. The oldest page is at the front of the queue and is the first to be removed when a new page is added
Belady’s anomaly
Phenomenon which means it is possible to have more page faults when increasing the number of page frames
Optimal page replacement
Page replacement algorithm that looks forward in time to see which frame to replace in the event of a page fault
Least recently used (LRU) page replacement
Page replacement algorithm in which the page which has not been used for the longest time is replaced
