Computer Science
Give 4 functions of the OS
- User Interface
- Memory management
- File management
- Security
- Interrupt handling
- Processor scheduling
What does the OS do
Hides the complexity of the hardware from the user by providing a user interface
What are pages?
Avavilable memory which is physically divided into fixed size chunks
Why is memory management important
- It allows programs to share/allocate memory to each other
- It allows programs larger than RAM to run
- Organises RAM use by converting logical addresses to physical addresses
Give 3 features of paging
- Memory is physically divided into fixed size chunks
- Each page has an address
- Used for virtual memory
Define 'Segmentation'
Where memory is logically divided into segments which acn be different lengths
Give 3 features of segments
- They're logical divisions
- They're complete sections of programs
- They're different sizes
Give 3 similarities of paging and segmentation
- Both allow programs to run even with insufficient memory
- Both are stored on a disk
- Both are transferred to memory when needed
What is virtual memory
Extra storage for when RAM is too full
What is disk thrashing?
Where pages are repeatedly swapped in & out of virtual memory causing the computer to slow down
What happens to sections of programs which aren't in use
They're temporarily moved into virtual memory by paging
What is an interrupt
A signal from an app/device to a processor indicating it needs attention
Give 3 examples of interrupts
- A printer running out of paper
- An error occurring in a program
- Power Failiure
At what point in the cycle does the CPU check for interrupts
At the end
Give 2 features of interrupts
- They're processed in the order of priority
- They can interrupt themselves if the new interrupt is of a higher priority
What does a distributed OS do
Coordinates the processing of a single job across multiple computers
Give an example of where a distributed OS can be used
In an online shopping site, where one server handles your basket whilst another handles querying of items
What is an embedded OS
An OS that provides limited specialist functionality
Give 2 examples of devices with embedded OS's
- Washing machine
- Traffic lights
- Air Fryer
- Tumble dryer
What is a real time OS
An OS designed to perform a task within a guaranteed time range
Give examples of devices that operate in real time
- Hospital monitoring machines
- Burglar Alarms
- Smoke detectors
- Aircraft autopilot systems
When are real time OS's usually used
In safety critical environments
What does BIOS do and what is it responsible for and where is it stored
- It boots up the computer
- Responsible for loading the OS when the computer switches on
- Stored in ROM
What's the first thing BIOS does
Checks if the hardware it needs is connected and working using a power on self test(POST)
What does the bootstrap (boot loader program do)
The program responsible for starting up the OS
Where are the BIOS settings stored and why?
Stored in flash memory so they can be changed and retained when switched off
What is a device driver
A software that enables communication between the OS & a hardware device
What is a driver
A program that provides an interface for the OS to interact with the user
Why are drivers important
To allow the OS to control hardware devices
What is a virtual machine
Where an entire OS runs inside another OS
What can a virtual machine be used for
They create isolated test environments that leaves the host OS unaffected. This allows a developer to see how their software affects system performance
Describe the ISR routine
The processor checks for interrupts at the end of the FDE cycle. If there's an interrupt of a higher priority than the process being executed, the current contents in the special purpose registers are pushed into a stack. The interrupt is then executed. Once the interrupt is completed, the processor restores the contents of the registers.
How does a device driver work
It translates the OS's instructions into a series of instructions that the hardware will understand