Systems Software Flashcards
0
Q
Resource allocation
A
- The OS allocates resources to other programs such as applications. For example:
- Scheduler to share processor - batch, foreground/background, timesharing
- Memory management - e.g. Virtual memory paging, swapping memory contents to hard disc
- Ensures drivers are given access to hardware devices
- Mechanisms for accounting; limit enforcement -e.g. no. of pages printed, file space per user etc.
1
Q
Single User Operating System
A
- This is a program that controls the entire operation of the computer and any devices that are attached to it.
- The OS is often thought of as a series of modules or layers.
- One design is as follows:
- Command Language Interpreter is the layer that the user interacts with to give instructions to the computer. It can be command-driven, menu-driven or a GUI which may use a WIMP system.
- Memory Management System controls where programs and data are placed in main memory. Many OS’s allow more than one program to be in memory at the same time. MMS tries to make sure that any program does not overwrite any other program (including the OS itself!).
- File Management System deals with the user of the computers backing storage devices. It uses part of the disc as a file catalog, which holds details of where data is stored on disc. Files are organised into a hierarchical filing system storing files in separate directories and subdirectories.
- Input Output System communicates directly with peripherals and handles the transfer of data between peripherals and the CPU.
- Kernel manages processes (when a program runs it starts a process and this may start further processes) and handles interrupts.
- One design is as follows:
- The layers work together to carry out operations, data being passed between them.
2
Q
Operating system can be ROM based or disc. based
A
- If disc based, then there must be a small part of the OS in ROM - the bootstrap loader - to load the main OS from disc to RAM.
3
Q
What additional features are provided by a Network Operating System?
A
- Multi-user access and security. If more than one person can access the system, then they need to ‘log on’ by giving an ID and password.
- File Server. Different users have different levels of access to the files e.g. file read and write privileges for a certain file.
- Print Server. The OS may provide a print server program to queue print jobs for all users, using a central printer spooler.
4
Q
Utility Software
A
- Utility programs are programs that aid the maintenance of the computer. They are not normally essential for the running of the computer and are usually kept on disc until needed. They include:
- Virus Checkers
- Scans discs/memory for viruses
- Disc Editors
- Allows the user to view the bytes of data held on disc and make changes to them. This is useful if disc errors occur to allow for data to be repaired or
parts of files to be extracted.
- Allows the user to view the bytes of data held on disc and make changes to them. This is useful if disc errors occur to allow for data to be repaired or
- Disk Defragmenter
- When discs have been used many times (i.e. files saved and deleted from them), as the disc fills up, free space appears between sectors with data, files have to be split up into these gaps as there is no room to save them in one continuous place. This makes loading programs slow as lots of fragments of file have to be found and linked. The defragmenter program moves files around on disc until they are all stored in consecutive sectors and the free space is maximised.
- Virus Checkers
5
Q
Standard Graphics File Formats
A
- JPEG - Joint Photographic Expert Group
- GIF - Graphics Interchange Format
- TIFF - Tagged Image File Format
6
Q
JPEG
A
- Compression
- Yes, lossy - can be varied - more compression, less resolution
- Colour depth
- Up to 24 bit
- Supports transparency
- No
- Supported on Web Pages
- Yes
- Used for
- Photographs, pictures on Web
7
Q
GIF
A
- Compression
- Yes, lossless
- Colour depth
- Up to 8 bit
- Supports transparency
- Yes
- Supported on Web Pages
- Yes
- Used for
- Web Graphics with blocks of colour
8
Q
TIFF
A
- Compression
- Not in standard TIFF
- Colour depth
- 24 bit colour or 8 bit greyscale
- Supports transparency
- No
- Supported on Web Pages
- No
- Used for
- Saving high resolution graphics
9
Q
Malicious Programs
A
- Virus
- Trojan Horses
- Worms
10
Q
Definition of a Virus
A
- A computer virus is a small program written to alter the way a computer operates, without the permission or knowledge of the user.
- A virus executes itself and will replicate, e.g. it may replace other executable files with a copy of the virus infected file.
- Viruses can infect desktop computers and network servers alike.
11
Q
Types of Virus
A
- File viruses
- Infect program files - normally executable code, such as .com and .exe files
- Can infect other files when an infected program is run from floppy, hard drive, or from the network
- Boot sector viruses
- Infect the system area of a disc - i.e. the boot record on floppy discs and hard discs
- Activate when the user attempts to start up from the infected disc
- Macro viruses
- The virus code written as a macro mainly infects data files (especially Microsoft Office files)
- Because of the ease with which these viruses can be created, there are now thousands of them in circulation
12
Q
Virus Actions
A
- Replication
- They spread as files are copied and sent between computer users.
- Camouflage
- It is possible for a virus to avoid detection by changing its characteristics from that which detection software is programmed to look for.
- Watching
- The virus damage routines may activate when certain conditions are met e.g. opening a particular application or on a particular date.
- Delivery
- This is how the virus gets from one computer to another:
- Infected disks brought in from the outside.
- E-mail now provides the ideal delivery vehicle.
- This is how the virus gets from one computer to another:
13
Q
Trojan Horses
A
- The difference between Trojan horse programs and true viruses is that Trojans do not replicate themselves.
- Trojans contain malicious code that when triggered cause loss, or even theft, of data.
- For a Trojan horse to spread, you must, invite these programs onto your computers - e.g. by opening an email attachment or downloading and running a file from the Internet.
14
Q
Worms
A
- Worms spread from computer to computer, but unlike a virus they do not infect other files.
- A worm takes advantage of data transport features on your system e.g. using email, which allows it to travel unaided. It can send out hundreds or thousands of copies of itself.
- The end result in most cases is that the worm consumes too much system memory (or network bandwidth), causing Web servers, network servers, and individual computers to stop responding.
