1.2.1 - systems software Flashcards
7, 8 (30 cards)
operating system
Controls the hardware and software of a computer system and provides a user interface.
Name the 5 types of operating systems.
- multi-tasking
- multi-user
- distributed
- embedded
- real-time
multi-tasking OS
Each active program is scheduled to receive a slice of processing time in quick rotation, giving the impression they are operating at the same time.
multi-user OS
Allows more than one person to use a computer at the same time.
distributed OS
Combines the processing power of multiple computers across a network for a single task.
embedded OS
Tend to run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory.
– 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
real-time OS
Processes have to be guaranteed to execute within a known time frame.
Basic Input Output System (BIOS)
Responsible for loading the OS when the computer first turns on. Initialises and tests the system hardware components.
bootstrap
Used to load the OS kernel into memory.
device driver
Software that tells the OS how to communicate with a device.
virtual machine
A program that has the same functionality as a physical computer.
5 functions of an operating system
1- memory management
2- interrupt service routines
3- processor scheduling
4- backing store management
5- management of all input and output
paging
- memory is split into pages of size 4Kb each
- a process currently in memory may be held in several non-contiguous pages
- a page table uses mapping to store a link between the physical memory address and the logical address space of each process
segmentation
The logical division of address space into varying length segments based on the program’s structure.
interrupt
A signal from a software program, hardware device or internal clock to the CPU.
When does a software interrupt occur?
When an application program terminates or requests certain services from the OS.
example of a hardware interrupt
‘printer out of paper’
interrupt service routines
- suspends execution of running process
- disables interrupts of a lower priority
- puts values of registers onto system stack
- interrupt service routine is called
4 objectives of a scheduler
1- maximise output
2- be fair to all users on a multi-user system
3- provide acceptable response time to all users
4- ensure hardware resources are kept as busy as possible
round robin scheduling
Each process is given a time slice controlled by an interval timer. If the process does not complete before its time expires, the despatcher gives the CPU to the next process. Guarantees a reasonable response time for all users.
first come first served scheduling
Jobs are processed in the order in which they arrive. No system of priorities.
shortest remaining time scheduling
The process with the smallest estimated time to completion is run next. However, it requires knowledge of how long a job will take. Possible for batch jobs like payroll.
shortest job first scheduling
The process with the smallest estimated running time is run next.
multi-level feedback queues scheduling
This algorithm is designed to:
- give preference to short jobs
- give preference to I/O bound processes
- separate processes into categories based on their need for the processor
