Unit 2: system software

Question 1

what is an operating system?

Answer 1

An operating system is a program or set of programs that manages the operations of the computer for the user. it acts as a bridge between the user and the computers hardware, since the user can’t communicate with the hardware directly

Question 2

where is the operating system held and how is it loaded?

Answer 2

The operating system is held in permanent storage, for example on a hard disk. A small program called the loader is held in ROM. when a computer is switched on, the loader in ROM sends instructions to load the operating system by copying it from storage into RAM

Question 3

What are the functions of an operating system?

Answer 3

An operating system disguises the complexities of managing and communicating with its hardware from the user via a simple interface.

Apart from providing a user interface, the operating system has to perform the following functions:
-Memory management
-Interrupt service routines
-Processor scheduling
-Backing store management
-Management of all input and output

Question 4

Describe Memory management:

Answer 4

Each program, open file or copied clipboard item, for example, must be allocated a specific area of memory whilst the computer is running. should a user wish to switch from one application to another in a separate window, each application must be stored in memory simultaneously. The allocation and management of space is controlled by the operating system

Question 5

Define Paging and Segmentation:

Answer 5

Paging and segmentation are two different techniques for making the optimum use of memory by splitting it into small sections
Paging:
this is where the memory is divided into fixed sized pages of 4Kb each, and a process currently in memory may be held in several non-contiguous pages.
Example:
Imagine a program which uses 15Kbof consecutive memory addresses - these logical memory locations may be physically stored in four separate pages anywhere within the physical memory space.

Segmentation:
is the logical division of address space into varying length segments which depend on the program structure. As with paging, it is possible to load only a part of a program into memory initially

Question 6

Define virtual memory?

Answer 6

Memory is limited on the computer, so as more and more jobs are loaded into memory, the operating system may swap temporarily inactive jobs out to disk , thus using secondary storage as an extension of memory to make room for the next job which has a share of processor time