1.2 Software Flashcards
S (53 cards)
What is an os
Program or set of programs that manages the operations of the computer for the user.
Acts as bridge between user and computers hardware
Where is the os stored
Permanent storage e.g) hard disk
What is the loader
Small program held in ROM that send instructions to load the os by copying it into RAM while the computer is switched off.
What are the functions of the os (5)
Memory management
Interrupt service routines
Processor Scheduling
Backing store management
Management of all input and output
How does memory management work
Each program is allocated a specific area of memory whilst the computer is running.
How does paging work
Memory Is divided into fixed size pages and process held in memory may be held in non-contagious pages
How does a page table work
It uses mapping to store a link between the physical memory address and the logical address space of each process
How does segmentation work
Logical division of address ace into varying length segments depending on the program structure.
What happens when a computer has insufficient memory
Deterioration in performance as pages are swapped in and out of RAM to the point where the os is spending time swapping pages in and out
What is an interrupt? +examples
Signal from a software program, hardware device or internal clock to the CPU.
A software interrupt occurs when an application program terminates or requests certain services from the os.
A hardware interrupt may occur when an I/O operation is complete or an error occurs
Interrupts can be triggered regularly by a timer, allowing for multitasking
What happens when the CPU receives and interrupt signal
It suspends execution of the running program or process and disables all interrupts of a lower priority.
It then puts all the value of the PC and each register onto the system stack while an interrupt service routine is called to deal with the interrupt.
Once the interrupt has been services the og values of the registers are retrieved from the stack and the process resumes from where it stopped.
How is multitasking done
Computer carries out small parts of multiple larger tasks in turn, the processor can give the appearance of multitasking
What is the schedular
OS module responsible for ensuring that processor time is used as efficiently as possible
What are the objectives of a schedular
Maximise throughput
Be fair to all users on a multi user system
Provide acceptable response time
Ensure hardware resources are kept as busy as possible
How does round robin work
Each process is given a time slice, os sets and interval timer to generate interrupts at specific times.
How does first come first served work
Jobs processed in order they arrive
How does shortest time remaining work
Process with shortest estimated running time is run next.
How do multi level feedback queues work
Gives preference to short jobs and I/o bound processes.
Separates processes based on need
What is backing store management
Where files and applications are loaded from memory into.
os keeps directory of where files are stored
Also needs to know areas of free storage
What is peripheral management
A process carried out by the operating system managing the way peripherals (hardware) interact with software
What is a buffer
Area of memory where for example data to be printed can be stored so the CPU can continue with another task. It compensates for the difference in speed between the output device and CPU
What is a distributed operating system
Form of parallel processing system that spreads the load over multiple computer servers. A job is split into several tasks run on a separate computer, coordinated by the os
What is a multi tasking system
Running multiple tasks at the same time, switching between them so each one appears to be the only one running.
What is a multi user system
A single powerful machine or supercomputer is connected to dozens or hundreds of terminals all using the mainframe CPU. Each user gets a slice of processor time based on scheduling algorithm.
