Unit 2 - System Software

Question 1

List all facilities of an operating system and what they do (treat this as a high mark question and go into detail)

Answer 1

Facilities:

User Interface - Puts computer language into text, images or other languages for humans to interact with.
Examples:
Command-line interface
Batch based interface
Graphical User Interface

Program Execution - Loads a program into memory and runs that program, also must be able to end execution.

File system manipulation - Programs need to be read and written as files and directories. Also allows users to create, load, move, read, edit or filter files.

Input / Output Operations - A program may require I/O, which may involve a file or other I/O devices. Users cannot directly govern the I/O devices. So, the OS provide a means to do I/O Input / Output operation which means read or write operation with any file.

Communication - Processes need to swap over information with other processes. Processes executing on the same computer system or on different computer systems can communicate using operating system support. Done using shared memory or via message passing.

Resource Allocation - When multiple jobs are running at the same time, the OS needs to allocate resources to all of them. Resources can be CPU cycles, main memory storage, file storage and I/O devices.

Error Detection - Errors may occur within CPU, memory hardware, I/O devices and in the user program. For each type of error, the OS takes adequate action for ensuring correct and consistent computing.

Accounting - Keeps track of which users are using how much and what kinds of computer resources have been used for accounting or simply to accumulate usage statistics.

Security and protection - Ensuring all access to system resources in a controlled manner. For making a system secure, the user needs to authenticate him or her to the system before using it.

Question 2

What is memory management?

Answer 2

A PC allows a user to be working on several tasks at the same time. The allocation and management of space is controlled by the OS

Question 3

What are paging and segmentation?

Answer 3

Paging and segmentation are two different techniques for making the optimum use of memory by splitting it into small sections.
Using a paging system, memory is divided into fixed pages of 4Kb each and a process currently in memory may be held in. A page table uses mapping to store a link between the physical memory address and the logical address space of each process.
Segmentation is the logical division of address space into varying length segments that depend on the program structure. As with paging, it is possible to load only a part of the program into memory

Question 4

What are interruptions?

Answer 4

A signal from a software program, hardware device or internal clock to the CPU. “Printer out of paper” - is an example of an interrupt.

Question 5

Intrerupt service routines

Answer 5

Interrupts are assigned priorities and lower priority interrupts may be disabled. Examples are given in order of descending priority:
Power Fail
Clock interrupt
And I/O device signalling an interrupt

Question 6

What is Round Robin?

Answer 6

Processes are despatched on a first in first out basis with each process given a limited amount of CPU time called a time slice or quantum.

Question 7

What are distributed operating systems?

Answer 7

A DOS is a form of a parallel processing system which spreads the load over multiple computer servers. A job is split up in several tasks and each of these is run on a separate computer, coordinated by the operating system, in a way in which it appears to be a singular system. Linux and windows are all available in distributed versions

Question 8

What’s a multi-tasking system?

Answer 8

• may run on a standalone computer such as a PC / Laptop

- Can multiple tasks at the same time

Question 9

How does a mobile OS work

Answer 9

Have two operating systems: main - operating UI
-app software
real time OS : operates
radio /hardware

Question 10

What is an Embedded operating system?

Answer 10

Microwaves / Washing machines use this

• minimal user interface
• it will accept input from sensors and send output to control devices
• limited RAM
• no permanent data storage

Question 11

What is a real-time operating system?

Answer 11

Used in aircraft or safety-critical systems
- it must respond very quickly to any inputs or sensors
- it must be able to deal with many inputs
- it must have failsafe mechanisms designed to detect and take appropriate action if a hardware component fails
i- it must have back up hardware

Question 12

What is the BIOS and what does it do?

Answer 12

A program that gets your computer started when you turn it on. It’s stored in the ROM

Question 13

What is a virtual machine?

Answer 13

Can be defined as any instance where software is used to take on the function of the machine, including executing intermediate code or running an os within another.

Question 14

What is system software and what does it do?

Answer 14

Needed to run the computer’s hardware and apps:

Includes OS, utility programs libraries and programming languages translators

Question 15

What are some functions of the OS?

Answer 15

Resource management - hardware, memory disk, drives etc:
provision of a user interface to enable users to perform tasks such as running application software, changing settings on the computer, downloading/installing new software

Question 16

What is a utility program?

Answer 16

System software designed to optimised the performance of the PC - such as restoring corrupted files compressing data

Question 17

What is disk defragmentation?

Answer 17

The program that will organise a magnetic hard disk - this makes reading a file quicker.

Question 18

What is a virus checker?

Answer 18

A virus checker is a utility that checks your hard drive and depending on the level of protection offered also emails and downloads

Question 19

What is general-purpose software?

Answer 19

It could be word - processor, spreadsheet or graphics packs. They can be used for many purposes

Question 20

What is a special purpose software

Answer 20

It performs a specific task, examples include payrolls and hotel booking systems.

Question 21

Off the shelf vs bespoke software

Answer 21

Off the shelf:
Less expensive since the cost is shared among all the other people buying the pack
It May contain a lot of unwanted features and some desirable and non-essential features may be missing
Read to be installed immediately
Well documented, well tested and error-free
Bespoke software:
More costly and requires expertise to analyse document requirements
Features to user requirements and other features can be added as needs arise
It May take a long time to develop
It May contain errors that do not surface immediately

Question 22

Open Source vs Closed Source

Answer 22

Open source:
Software is licensed to use but there is no charge for the license. Anyone can use it
Open-source software may be distributed with the source code so anyone can modify it
Developers can sell software they have created
Any new software from the open-source must also be able to open. This means that it must be distributed in a form that other people can read and edit
Closed source:
There will be restrictions on how the software can be used for example it may permit only a number of people to use it at once
The company that wrote it will hold the copyright. The users will not have access to the source code.
- support from the company
- regular updates

Question 23

What is an assembler?

Answer 23

An assembler is a program that takes basic computer instructions and converts them into a pattern of bits that the computer’s processor can use to perform its basic operations. Some people call these instructions assembler language and others use the term assembly language

Question 24

What is a compiler?

Answer 24

A program that translates a high-level language such as python into executable machine code that a computer can process.

Question 25

What is an interpreter?

Answer 25

An interpreter is a different type of programming language translator. It scans for syntax errors, translates into machine code and runs it

Question 26

What is bytecode?

Answer 26

After a compiler or interpreter is used it results in bytecode that is executed by a bytecode interpreter.
Advantages of bytecode:
Platform independence
Acts as an extra security layer between computer and program and you then execute java bytecode rather than the program itself.

Question 27

What are the advantages and uses of compilers and interpreters?

Answer 27

A compiler has many advantages over an interpreter:
The object code can be saved on disk and run whenever required without the need to recompile. However if an errored is discovered the whole program has to be recompiled.
The object code executes faster than interpreted code
The object code produced by a compiler can be distributed or executed without having the compiler present
the object code is more secure as it cannot be read without a great deal of reverse engineering.
An interpreter has some advantages over a compiler:
platform independence.
it is useful for program development as there is no need for lengthy recompilation.

Question 28

Disadvantages of an interpreter?

Answer 28

The program may run slower than a compiled program because each statement has to be translated to machine code each time it is encountered. So if a loop of 10 statements is performed 20 times all 20 statements are interpreted 20 times

Question 29

What are the stages of compilation?

Answer 29

Lexical analysis:
Superficial spaces are removed
All comments are removed
Simple error checking is performed
Keywords constants and identifiers are replaced by unique symbols.

Question 30

What is syntax analysis?

Answer 30

Process of determining whether the sequence of input characters for a valid sentence in the language.

Question 31

What is Parsing?

Answer 31

Parsing is the task of applying the set of rules to each statement to determine if it’s valid. Stacks will be used to check.

Question 32

What are linkers and loaders?

Answer 32

Linkers put the appropriate machine address at the external call and return instructions so that modules can be linked together appropriately
A relocating loader can load the object code anywhere in memory, provided the programmer has used no absolute addresses.

Question 33

What is a library?

Answer 33

Library programs are ready-compiled programs grouped in software libraries that can be loaded and run when required. Most languages have their own libraries of pre-written functions.

Question 34

What are the advantages of using library routines?

Answer 34

They are tested and error-free

save the programmer time in “re-inventing the wheel” to write code themselves to perform common tasks.