1.2.1 Systems Software Flashcards
1.2.1 A)
What is an os
collection of programs that work together to give an interface between user and computer
1.2.1 B)
Why is memory managment needed
memory must be shared fairly between multiple programs as ram not large enough to hold all. so os allocated amount of procosser time each task gets
1.2.1 B)
What are the three types of memory managment
paging, segmentation and virtual memory
1.2.1 B)
What is paging
memory is split up into equal sized section these can be swapped in and out of memory from secondary storage. However could seperate instructions like a loop.
1.2.1 B)
What is segmentation
splits memory into logical size division which may vary in size. Represents the structure and logical flow of program.
1.2.1 B)
What is virtual memory
uses a section of seconday storage to act as ram. part of program not in use temp moved through paging.
However disk thrashing can occur, this is when the computer freezes due to pages being swapped to frequently so they are spending move time moving instructions then executing them.
1.2.1 C)
What is an interrupt
Are signals generated by software or hardware to indicate to the cpu that a process needs attention
1.2.1 C)
How are interrupts stored
based on priority on urgent stored in order of priority within an abstract data structure callled priority qeue which is in the interrupt register
1.2.1 C)
How does Interrupt servies routine work
1)At the end of the fde cycle processor checks content of interrupt register
2) if an iterrupt of higher prority is found the content of the memory registers are temp transfered to a stack
3)cpu then responds to interrupt by loading the correct interrupt servies routine into the ram. A flag is sent to signal that the ISR began
4) Queue checked again for interrupts, this is repeated untill all have been servises. All interrupts have higher priorty then regular programs
5) pop the frame of the stack to continue the fde cycle
1.2.1 D)
What is scheduling
function of OS to ensure all sections of programs being run (jobs) recieve a fair amount of processing time.
How long , what next ??
1.2.1 D)
What catagories can schedulings algorthims be placed into
pre-emptive
non pre-emptive
1.2.1 D)
pre-emptive vs non pre-emptive
Pre - jobs are activly made to stop and start by using the os
non pre - once job starts left alone untill completion
1.2.1 D)
What are types of pre-emptive scheduling algorthims
Round robin
multi-level feedback
shortest time remaining
1.2.1 D)
What are types of non pre-emptive scheduling algorthims
First come first serve
shortest job first
1.2.1 D)
explain the round robin scheduling algorthim
Each job given section of processor time (slice) to execute. All jobs have equal time untill complete and removed from queue. Long jobs are ineff , doesnt take prority into account
1.2.1 D)
explain the first come first serve scheduling algorthim
Chronological order from joining queue
1.2.1 D)
explain the multi-level feedback scheduling algorthim
multiple queues with diffrent priorites , difficult to implicate
1.2.1 D)
explain the shortest job first scheduling algorthim
req processer to calc how task takes. risks processor stavation if continuious short jobs join queue
1.2.1 D)
explain the shortest time remaining scheduling algorthim
req processer to calc how task takes. risks processor stavation if continuious short jobs join queue but if a shorted job joins queue it will take priorty
1.2.1 E)
What are the diffrent types of OS explain
1) distributed - runs across multiple devices allowing the
load to be spread accross multiple computer cpus
2) Embedded - preforms a small range of specific tasks consumes less power
3) multi-tasking - multiple userrs make use of some computer must use scheduling alg risk of cpu starvation
4) real time - used in critcal time computers were takes happen in a guaranteed time frame
1.2.1 F)
What is BIOS
Basic input output system, first system to run pc relies on it for running tests before loading OS into memory
1.2.1 F)
What are the tests that bios carry out
1) POST - power on self test ensures hardware are correctly connected and functional
2) checks cpu clock , memory and cpu is operational
3) tests for external memory
1.2.1 F)
Why is bios needed
As OS can only be loaded into the RAM from secondary storage
1.2.1 F)
What is a bootstrap
Loads OS kernel into main memory
1.2.1 F)
What is a kernel in terms of BIOS and OS
Kernel ensures smooth OS interface between hardware and software
1.2.1 G )
What is a device driver
Program that provided by the OS allowing OS to interact with hardware by translating OS instructions into instructions the hardware will understand
specific to computers architecutre
1.2.1 H)
What is a virtual machine
A Virtual Machine (VM) is a computer resource that uses software instead of a physical computer to run programs and deploy apps
1.2.1 H)
What are the benifits of a virtual machine in terms of a server
can split a physical server into many so if one fails another can pick it up.
1.2.1 H)
What are the properties of a VM
+ve and -ve
Provides an environment with a translator to run intermediate code. +VE )This allows for an evironment for testing different OS saves time and money of purchasing another device with a different OS.
-VE ) can ve slower running intermediate code on a VM compared to low level code.
1.2.1 H)
What are some other uses for VM’s
Protection from malware - malware will effect the VM not the physical device its being run on.
Allows user to run incompatable software - able to run os specific programs like a console on a pc
1.2.1 H )
What is intermediate code
halfway between machine code and object code
often used in the process of compiling a high-level language into machine code
