The Operating System Flashcards
What is an Operating System?
An Operating System (OS) is software that manages computer hardware and software resources.
All computer programs (other than basic firmware systems) require an operating system to function
It provides a layer of software services which are used to interact with the hardware. It acts as a layer between the software (and user) and the hardware.
Why will not always the OS be loaded into main memory
Operating systems can be extremely large and so not all of the operating system will be loaded into the main memory.
The Kernel or main part of the Operating System is loaded into RAM when the computer boots up and this is responsible for managing processes, hardware and other important low-level tasks.
What are the functions of an OS
Process Management: Ensuring that different processes/programs can be run and in a multi-tasking Operating System appearing to run simultaneously using scheduling
Input/Output Management: Communicating with devices such as keyboards, mice, printers, monitors, etc.
Backing Store Management: Ensuring data can read/written to disk drives, maintaining a hierarchical file system, etc.
Memory Management: ensuring that programs and data can share memory and are stored correctly without interfering with each other
Human Computer Interface: To display information to the user and accept input.
Utilities: software that comes with the OS to help with the running of the computer, e.g. File Management, backup, virus scanning, etc.
Security: OSs will typically have security built-in such as login/passwords, encryption, file access rights, etc.
What are the functions of an OS
Process Management: Ensuring that different processes/programs can be run and in a multi-tasking Operating System appearing to run simultaneously using scheduling
Input/Output Management: Communicating with devices such as keyboards, mice, printers, monitors, etc.
Backing Store Management: Ensuring data can read/written to disk drives, maintaining a hierarchical file system, etc.
Memory Management: ensuring that programs and data can share memory and are stored correctly without interfering with each other
What are the functions of Hardware drivers
Consider a device such as a screen (but this would apply to all device types);
There are potentially hundreds of different types of screen, by different manufacturers, that use different cable types, etc;
Therefore the Operating System has to have a generic/standard way of talking to screens;
This generic communication isn’t understood by the hardware itself so the hardware manufacturers produce software called hardware drivers and these perform the translation between the generic OS instructions and the specific binary control signals that the hardware understands;
Managing backing store
Storage devices are managed by the OS which will be able to read and write files and folders/directories and maintain a hierarchical structure, file access rights, etc;
Typically access rights can be set to specify which users or groups of users are able to read and/or update each file or folder
Files can become fragmented as discussed in topic 2.1 and operating systems may periodically defragment the drives automatically.
Where is information stored in an index
Hierarchical structure - Backing store
The root folder/drive of a directory can contain files or sub-folders/directories
These sub-directories can also contain files or further sub-directories, etc. in a tree structure:
The directories can be ordered in a logical way;
For fast access to files;
For added security (see below).
Access rights can be set at a directory or file level to determine whether a particular user is able to access the folder, whether they have just read access, read or write, etc;
On a network drive each user may have a folder for their documents. Each user folder would have read and write access for the user and perhaps the Administrators group. In a school system a teacher might be given read access to each pupil’s folder.
Name the different types of utility software
File Management: e.g. to copy, move, rename, delete files and directories;
Compression Software: to compress the size of files (they will be slower to open or execute each time as they will need to be decompressed first) – see topic 1.3;
Task Managers: to view processes/programs that are running, check how much processor time they are taking up and kill unresponsive processes if necessary;
Anti-virus software: needs to be updated at least daily;
Backup software: to allow data to be backed up to an external drive or cloud storage.
List the different types of Human Computer Interface
Operating Systems use a variety of user interfaces. It is important to design systems that are appropriate to the variety of different users at all levels and in different environments.
Examples
Command Driven (e.g. MS-DOS, Unix)
WIMP (windows, icons, menus and pointers) e.g. Windows, Apple OSX
Touch, voice, etc.
Options for accessibility (to allow easier use by people with particular disabilities)
List the types of OS
Single tasking - the OS supervises the loading and running of one program at a time and the input/Output of data from peripheral devices.
Batch system - will run a series of programs or jobs allocated to it in a batch file. This may be ran overnight e.g. a master file with a transaction file. Once started it doesn’t need human interaction to run
Multi programming - This type of OS allows more than one program to be held in main memory at the same time. Although a single CPU can only be running the code for one of the programs at a time, it does allow it to have one program performing Input/Output operations while it is processing another or if time-slicing is used it can give each process a fair allocation of its processor time. Multi-programming usually involves either or both multi-access and multi-tasking
Multi-user / Multi-access - Traditionally this is the type of OS used on main-frame computers and is another form of multi-programming. The OS handles several different programs running at once but these programs can be owned by different users attached to the computer from terminals. The processor again allocates time-slices to each program so that each user’s program appears to be running at the same time. This is often referred to as a time sharing system.
Multi-tasking - A multi-tasking OS is an example of multi-programming and the terms are often used interchangeably. An example of a multi-tasking OS is Windows 10, where there can be different programs in memory and appearing to run at the same time. Users can switch between tasks/applications. Obviously a single processor is actually only able to run one process at a time and a time-slice based scheduling policy is used.
Stand-alone - A stand-alone OS is one which runs on a single computer and is not designed to be connected to others via a network (e.g. Internet). MS-DOS had no built-in networking facilities so was an example of a single-tasking, stand-alone system. This may benefit security – reduced chance of hacking/unauthorised access via a network, not susceptible to network or server failure. However it can’t communicate or share devices, software, data.
Slide 20
