1.2.1 Systems Software

Question 1

Operating System (OS)

Answer 1

A program or set of programs that manages the operations of the computer for the user. Allows the user to interact with the computer’s hardware via a User Interface (UI)

Question 2

Functions of an OS

Answer 2

• Provides a UI
• Memory management
• Interrupt Service Routines
• Processor scheduling
• Backing Store management
• Management of all input/output

Question 3

Paging

Answer 3

Memory is divided into fixed sizes. A page table uses mapping to store a link between the physical memory address and the logical address space of each process.

Question 4

Segmentation

Answer 4

Local division of address space into varying length segments which depend on the program structure.

Question 5

Virtual Memory

Answer 5

Secondary storage is used as an extension of memory to make room for the next process.

Question 6

What happens when the CPU receives an interrupt signal?

Answer 6

• Suspends execution of the running process and disables all interrupts of a lower priority.
• All values of the PC/registers are put onto the system stack.
• An interrupt service routine is called to deal with the interrupt, depending on the priority.
• The original values of the registers are retrieved from the stack and the process resumes from where it left off.
• A test for interrupts is carried out at the end of the FDE cycle.

Question 7

Round Robin

Answer 7

• Programs despatched on a FIFO basis.
• Each process is given a time slice (limited amount of CPU time)
• If the process is not completed at the end of its time slice, or before a higher priority interrupt occurs => moves on to the next process

Question 8

First come first served

Answer 8

Jobs are processed in the order they arrive => with no system of priorities

Question 9

Shortest remaining time

Answer 9

The process with the smallest time to complete, estimated by the user, is run next.

Question 10

Shortest Job First

Answer 10

The process with the smallest estimated time is run next.

Question 11

Multi-level feedback queues

Answer 11

Algorithm designed to give preference to short jobs/IO-bound processes, and separate processes into categories based on their need for the processor.
This maximises processor use.

Question 12

Distributed OS

Answer 12

• A form of a parallel processing system => spreads the load over multiple computer servers
• A single job is split up into several tasks => each is run on a separate computer

Question 13

Multi-Tasking System

Answer 13

The OS can run many jobs simultaneously/at the same time.

Question 14

Multi-User System

Answer 14

Many users can use the same OS at the same time.

Question 15

Embedded System

Answer 15

Designed for one specified purpose. Has a minimal UI, accepts input from sensors, and has limited RAM.

Question 16

Real-time OS

Answer 16

Responds very quickly to any inputs or sensors simultaneously, has failsafe mechanisms, and incorporates redundancy.

Question 17

Basic Input Output System (BIOS)

Answer 17

• Stored in ROM.
• Initialises/tests the system hardware components and loads the OS from the hard disk into RAM.
• Used to provide an abstraction layer => allows a consistent way for apps/OS to interact with input/output devices

Question 18

Device Drivers

Answer 18

Provides a software interface to a particular hardware device, which enables the OS to access hardware functions without needing to know the details of the hardware being used.
They are hardware-dependent and OS-specific.

Question 19

Virtual Machine

Answer 19

Software is used to take on the function of the machine by running an OS within another to emulate different hardware.