*IN PROGRESS* OPERATING SYSTEMS Flashcards
(27 cards)
Explain the role of device drivers when using input and output devices on a computer system
- A program/software
- That controls a piece of hardware
- Providing an interface/bridge between the device and operating system
Give examples of a device driver that a home user would need
- Printer driver
- Webcam driver
- Sound card driver
- Graphics card driver
Describe the similarities between paging and segmentation
- Both ways of partitioning / splitting up memory
- Use virtual memory / backing up to swap parts of programs
- Allow programs larger than memory to run / insufficient memory
- ALlows programs to be stored in memory non contiguously
Give the name of three other types of operating system, and for each state its purpose.
Multi-tasking…
…runs multiple programs at the same time
Multi-user…
… allows multiple users at the same time (must
be clear that candidate is not discussing an OS
that simply has multiple accounts)
Distributed…
…allows multiple computers to work together on
a single task
Embedded…
…has a dedicated/limited function
…is read-only/ cannot be changed
Explain why the computer’s operating system uses a first come first served algorithm
when sending documents to the printer.
For printer queue
All documents/users have equal priority
Whichever document is received first is printed first
First in First Out/ Last in Last Out
Explain why the computer’s operating system uses a round-robin algorithm for allocating
processor time.
To enable multitasking to take place
To switch between active processes and those
running in the background
To limit each process to a certain amount of
time//allow processes an equal share of processor
time….
…to ensure the OS cycles through all processes //
the process then goes to the back of the end of the
queue
…so that users can receive an immediate response
…to handle an interrupt immediately
Explain why First Come First Served is a suitable scheduling algorithm for Arnold’s
router.
Jobs dispatched on a FIFO basis
Each job/packet is equal priority
Each job/packet switch has the same processing
time
The scheduling algorithm Arnold’s router uses is First Come First Served.
State the name of one other scheduling algorithm.
Round Robin
Multi-level feedback queues
Shortest job first
Shortest time remaining
Define the term ‘embedded operating system’.
System software/software used to
manage the device
Which is built into the device itself
Stored in the device’s ROM/cannot be
changed
Specific to the hardware/purpose
When running the anti-virus software, an operating system uses a scheduling algorithm to
determine an allocation of CPU time to the anti-virus software.
Explain why a First Come First Served scheduling algorithm would not be suitable in this
situation.
FCFS means jobs are completed in the
order they arrive
ineffective in catching viruses/the virus
may run first
…the virus checker may never run/take
a long time to start running
the virus checker may be continuously
running…
…this will temporarily stall the system/
all other processes have to wait.
Explain why the self-driving system will use a real-time operating system.
Needs to be able to respond instantly to
changes…
such as someone stepping in front of car (or
other sensible example)
RTOS offerss a guaranteed response time.
A non RTOS might be busy dealing with other
tasks and not respond until it is too late.
See And Believe is a company that specialises in computer-generated imagery (CGI) for films.
Producing CGI requires lots of processing power and so the company has a large number of high performance computers.
Explain why See And Believe would use a distributed operating system.
Allow multiple computers/resources…
…To be treated as one/work on the same problem
Meaning all the computers can work on producing
the same special effect.
State what is meant by the term real-time.
The system gives a response within a
guaranteed time frame
Explain why a real-time operating system would be suitable for Intensive Care Units.
If something happens to a patient, a
response must be immediate
Other types of system may have
delays in response
This could result in a patient not
receiving treatment in time
Explain why scheduling is necessary.
Process as many jobs as possible…
…in least possible time / quicker
Ensure all jobs are processed (fairly)
Maximise number of interactive users…
…with fast response times / real time
Efficient use of resources//processor time
A software development company is building an operating system for a mobile phone that is in the process of
being designed.
One of the developers is responsible for writing the code for what happens when the CPU receives an interrupt.
Outline what the code must do.
Complete the current FDE Cycle
- Check the priority of the incoming
interrupt.
- If its of a higher priority than the current
task.
- Contents of registers stored in
memory..
… in a stack.
- Flags are set to determine if interrupts are enabled /
disabled
- The relevant interrupt service routine is
loaded.
- ..by loading the relevant value into the
program counter.
- When the ISR is complete the previous
state is popped from the stack
- And are loaded back into the registers in the correct order
- Flag is reset
- If higher priority interrupt received during servicing of
interrupt…
…this is added to stack and new interrupt dealt with
An operating system uses scheduling. One method of scheduling is first come, first served.
Explain why the first come, first served scheduling method may not be efficient.
Once a job starts it prevents other jobs
from being processed
A job using a slow resource (eg printer)
wastes processor time
Describe the scheduling algorithms other than FCFS and RR
Shortest job first/ shortest remaining time
Process which has the shortest time (remaining) is
completed first
Multilevel feedback queues
Uses queues with different priorities
Jobs can be moved between queues
The operating system needs to load program C into memory but there is not enough
space. Describe how the operating system would use virtual memory to load program С.
Operating system uses area of secondary storage
as virtual memory.
Move unused pages/parts (of program A and/or
B) into virtual memory
Load program C into (physical) memory.
What is the purpose of an operating system
It is a system software
That provides the interface between the user and the hardware
How does an operating system handle multitasking
- When you have more than one program open and running at the same time
- The operating system allocates a small amount of time to each process and cycles between them
- As this happens so quickly, it appears as if multiple programs are executing simultaneously
How does an operating system handle user management/security
- Allows multiple users to log into the same computer
- The operating system will retain settings for each user such as icons, desktop backgrounds, etc
- Each user may have different access rights to files and programs
- A client-server network may impose a fixed or roaming profile for a user and manage login requests to the network
How does an operating system handle user interfaces
WIMP: Windows, Icons, Menus and Pointers
- Visual
- Interactive
- Intuitive
- Optimised for mouse and touch gesture input
What is memory management
Ensuring RAM is used efficiently and is not wasted
