ch16 Flashcards
bootstrap
program that loads par of the operating system into the main memory (RAM) from hard disk SSD and initiates the start up procedure in computers// a small program that is used to load other programs to ‘start up’ a computer
The flash memory is split into two parts
- the part where the OS resides, it reads only
- the parts where the apps and any associated data are stored
scheduling
process management which handles the removal of running programs from the CPU and the selection of new proccesses
direct memory access DMA controller
device that allows certain hardware to accesses RAM independently of the CPU
how does a DMA work
when the CPU is carrying i/o operations it is fully utilized during the entire read/write operations; the DMA frees up the CPU to allow it to carry out other tasks while the slower i/o operations are taking place.
1. the DMA initiates the data transfer
2. the CPU carries out other tasks while the data is being transferred
3. once the data transfer is complete, interrupt signals are sent from the CPU by the DMA
kernel
the core of an OS that controls process management, device management, memory management, interrupt handling and input/output file communications and communication between hardware software and memory
multitasking
function that allows a computer to process more than one task (process) at a time (a process is a program that has started to be executed)
two types of multitasking operating systems
1- preemptive: is a method of multitasking in which the operating system can interrupt the execution of a currently running task to allocate the CPU time to another task, typically based on the priority or the predetermined scheduling algorithm
2- non-preemptive: a multitasking method which voluntarily yields control of the CPU to other tasks. tasks will continue to execute until they relinquish control, typically by waiting for the input/output operations to complete
low level scheduling
method which decides which process should next take the use of CPU time based on priority level //// y 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
the states of a process which require execution. running, ready and blocked
condition when changing from one process state to another
table 16.3 pg 378
round robin scheduling
scheduling algorithm that uses time slices assigned to each process in a job queue
summarises what happens during the round robin process
1- each process has an equal time slices (known as a quantum)
2- when the time slice ends the low level scheduler puts the process back in the ready queue allowing another process to use the CPU
3- when the slice time ends, the status of each process must be saved to ensure it can resume from where it left off during the next allocation time of the CPU
4- the CPU registers’ contents, such as Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), and Accumulator (ACC), are saved to the process control block (PCB), with each process having its own PCB.
5- When the CPU switches to executing the next process (burst time), the previous process’s state is reinstated or restored, a process known as context switching.
name the four scheduling routine algorithms
1- first come first served scheduling (FCFS)
2- shortest job first scheduling (SJF)
3- shortest remaining time first scheduling (SRTF)
4- round robin
interrupt dispatch table (IDT)
table links a device description with the appropriate interrupt routine.
interrupt priority levels (IPL)
–values given to interrupts based on values 0 to 31.
paging
form of memory management which divides up physical memory and logical memory into fixed-sized memory blocks
segments memory
logical memory that is divided into variable-sized memory blocks
virtual memory
type of paging that gives the illusion of unlimited memory available
page replacement
occurs when a requested page is not in the memory and a free page cannot be used to satisfy allocation
what are the page replacement algorithms
1- first in first out (FIFO)
2- optimal page replacement
3- least recently used page replacement
4- clock page replacement/ second chance page replacement
first in first out
the OS 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 needs to be added.
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 page replacement
page replacement algorithm in which the page which has not
been used for the longest time is replaced
virtual machine
an emulation of an existing computer system. A computer OS running within another computer’s OS.
emulation
the use of an app/device to imitate the behaviour of another program/device
host OS
an OS that controls the physical hardware
guest OS
an OS running a virtual machine
hypervisor
virtual machine software that creates and runs virtual machines
how does an OS hide the complexities of the hardware from the users
1- using GUI rather than CLI
2- using a device driver (simplifies the complexities of a hardware interfaces)
3- simplifies the saving and retrieving of data from memory and storage device
4- carrying out background utilities such as virus scanning
