the operating system

Question 1

what is an operating system?

Answer 1

software that manages and controls the computer hardware + acts as an interface between user and the hardware
eg windows, macOS

Question 2

OS services (name 3)

Answer 2

• provides user interface
• runs software programs by loading code + data into RAM and activating CPU
• allows multiple programs active at same time by sharing processor time
• allows configuration of hardware eg screen resolution
• displays catalogue of programs and data files
• provides security to prevent unauthorised access

Question 3

how does the OS manage peripherals?

Answer 3

manages peripherals (inputs/outputs) by communicating and sending data output to them using drivers

Question 4

how does the OS manage memory?

Answer 4

OS loads data into RAM when needed and unloads it when it isn’t
partitioning
buffering

Question 5

partitioning

Answer 5

dividing memory into multiple partitions and allocating each partition to instructions and data for one specific task

Question 6

buffering

Answer 6

allocating part of memory to temporarily store data in transit between computer and a slower device eg webcam/printer
cannot be filled and emptied at same time so double buffer can be used so one can be filled while the other is emptied to speed up data transfer.

Question 7

how does the OS manage the backing store?

Answer 7

allocate physical disk space as files are added, edited or deleted providing hierarchical, searchable structure for users.

Question 8

utility software

Answer 8

software that performs tasks that support the operating system
analyses processes, optimises processes or maintains the system

Question 9

categories of utility software (name 4)

Answer 9

anti-virus
compression
debuggers
screensavers
system monitors
encryption
defragmentation

Question 10

anti-virus

Answer 10

checks the computer for malware and notifies the user of any is found

Question 11

compression

Answer 11

allows a file/folder to be reduced in size for storage or transmission

Question 12

debuggers

Answer 12

identify and help to resolve problems in software

Question 13

screensavers

Answer 13

starts automatically after a pre-set interval to prevent screen burn and save power

Question 14

system monitors

Answer 14

utilities allow the user to track memory and processor usage + network connection speed and more

Question 15

name 3 uses of a user interface

Answer 15

• allows copying/ deleting/ moving/ sorting/ searching of file or folders
• allows access to system settings such as hardware
• allows users to have more than one window open
• provides graphical user interface
• provides user with error messages

Question 16

modes of operation

Answer 16

different ways that operating systems have of working
batch processing
real time control processing
real time transaction processing

Question 17

batch processing

Answer 17

a series of tasks completed at the same time (normally without intervention overnight when resources are available)
uses a transaction file to record events and updates the master file at the end of the period
eg running pay roll, gas billing ( as bills are issued regularly in response to meter readings)
simpler/faster with transactions being stored in order they are recieved

Question 18

real time control processing

Answer 18

reacts to a signal to make changes which will take place immediately (but doesn’t need to happen quickly)
eg traffic lights changing or autopilot detecting obstacle and moving

Question 19

real time transaction processing

Answer 19

task completed immediately and the master file is updated when an occurrence is completed to give and accurate view of data at any time
much more complex algorithms
eg used to avoid double bookings at concerts

Question 20

master file

Answer 20

holds descriptive data (the actual data that is supposed to be processed) and holds the resultant data after the process is completed
data is held sequentially in key field order
eg customer details for electricity company

Question 21

transaction file

Answer 21

contains the transactions (changes supposed to be made to master file)
data is help serially in order it was collected
eg customer meter readings for electricity company

Question 22

singer user OS

Answer 22

single user can be active at any one time (can have multiple users but one one at a time)
protected with user names and passwords
home directories are created for each user with a hierarchical file structure
can also be a multi tasking OS

Question 23

multi user OS

Answer 23

system resources timeshared between multiple users at once - each can access their own terminals with usernames and passwords
often used on servers
can also be a multi tasking OS

Question 24

multi tasking OS

Answer 24

switching tasks in and out of the CPU done by the OS to give the impression it is running everything simultaneously
can falter if one process takes a lot of processing time or crashes as other processes may delay or become unresponsive

Question 25

multi programming OS

Answer 25

allows multiple processes to reside in main memory at the same time to make them appear to be processed by the computer's CPU simulaneously optimises use of CPU by preventing it from being idle while waiting for slower peripherals. OS may perform scheduling

Question 26

scheduling

Answer 26

a processor appears to carry out multiple processes at a time whereas it is actually just switching between them extremely quickly. scheduler ensures CPU is utilised as much as possible has different methods of scheduling: - first come first served - round robin - fixed priority

Question 27

first come first served scheduling

Answer 27

each process handled from start to finish in the order in which is arose

Question 28

round robin scheduling

Answer 28

each process received a fixed time slice and when time slice expired the CPU moves on to next process and come back to incomplete one later

Question 29

fixed priority scheduling

Answer 29

high priority processes jump the queue and are handled first. low priority processes can have status upgraded if they are left waiting for a long time

Question 30

time slice

Answer 30

a small chunk of processor time

Question 31

states of a process

Answer 31

ready - in main memory awaiting execution by CPU running - currently being executed by CPU blocked - awaiting access to a resource that is currently unavailable (needs intervention)

Question 32

polling

Answer 32

sending a signal to a device eg printer, to check if it is ready. will repeat until device is ready or computer has polled a predetermined number of times

Question 33

interrupt

Answer 33

a signal generated by hardware or software that puts the normal FDE cycle on hold and diverts CPU's attention to source of the interrupt has priority levels so another interrupt of higher priority can interrupt an interrupt a low level interrupt will not interrupt a high level task

Question 34

examples of hardware interrupts

Answer 34

mouse click keyboard press insertion of new piece of hardware

Question 35

examples of a software interrupt

Answer 35

detection of imminent power loss a runtime error eg attempt to divide by 0 software fault

Question 36

fixed partitioning

Answer 36

dividing memory into non-overlapping sections that are fixed in size process may be loaded into a partition of equal or greater size and is confined to that partition internal fragmentation can occur

Question 37

internal fragmentation

Answer 37

when a small process leaves unoccupied space in a partition

Question 38

variable partitioning

Answer 38

system for dividing memory into non-overlapping sections with variable sizes is more flexible than fixed and doesn't allow for internal fragmentation

Question 39

dynamic partitioning

Answer 39

system for making partitions during run-time according to process' needs instead of doing it during system configuration efficiently utilises RAM

Question 40

memory buffering

Answer 40

small block of memory in devices where current data is being held and is used to compensate for slower devices ensures work is not lost when the processor is busy eg key press on keyboard may be held in buffer if text doesn't appear when you are typing

Question 41

buffer process for storing and loading data from a device

Answer 41

chunk of data sent by CPU to device and stored in a buffer device will slowly save the data while CPU free do to other tasks when buffer is empty an interrupt is sent to CPU CPU processes interrupt by informing OS then more data is sent and cycle repeats

Question 42

double buffering

Answer 42

one buffer used to store the data the second buffer will process the data once the data is processed, data from buffer 1 sent to 2 and process repeated avoids delays and increases processing speed

Question 43

ping pong (method of double buffering)

Answer 43

buffer 1 holds data buffer 2 interrupts and sends the data buffer 1 interrupts and sends its own data while buffer 2 holds next set of data

Question 44

threading

Answer 44

a thread is a sequence of instructions that make up part of a process. 2 threads belonging to the same process can share resources.