Operating Systems

The operating system is a collection of programs that work together to tell the hardware what to do. They are necessary on all computer systems ranging from mobile phones right up to the most powerful supercomputers.

The Operating System:

• Provides a user interface (UI)
• Provides an interface between the running programs (applications)
• Manage the computer hardware and peripherals
• Manage programs installed and running
• Manage data transfer between memory locations, the CPU and secondary storage
• Provide a file system for storing and retrieving files
• Manage security and organising data so that it is not overwritten

(a peripheral is a hardware device that is outside the normal computer enclosure)

The available space in the primary storage is limited and the Operating System will allocate memory to each application as it needs it. The application will also hand back any RAM that it no longer needs. It is very likely that the space available will be less than is actually needed, and the operating system will use techniques such as virtual memory to temporarily use the secondary storage space to store excess data.

When a program is closed (which may be because of a "crash" where an error causes the program to suddenly stop), the operating system will try to reclaim all the allocated memory so that other programs can use it.

Occasionally, poorly written software may not hand back all the memory it has been allocated, and this situation is known as a "memory leak" which will gradually lock up the computers RAM and may cause a complete system crash. Whenever the computer is re-booted, the RAM is completely cleared.

Multi-tasking

As well as managing the amount of RAM and other system resources that each application requires, the operating system has to divide the amount of processing power that is available between all of the programs that require it. This may include each program that is loaded, but also many background tasks such as transferring files to storage, printing documents, anti-virus checks and many many more.

The operating system does this by allocating small "slices" of time, which may each last for hundredths of a second, to each program. Once the program has used its allocation, then the operating system will pass control to the next one in the queue. This will repeat continually and it will appear that the computer is doing more than one thing at once, but in reality it is switching between the applications very rapidly.

Peripheral Management and Drivers

It is possible to connect a very wide range of devices to a modern computer and we expect that the system will automatically deal with each new piece of hardware and allow us to use it without issue. This is done by using a piece of software known as a "driver". The driver will deal with the specific hardware and pass any signals to the operating system in a standard way. A good example of this is the computer mouse, you can connect many different types of mouse such as roller ball mice and even "gyro mice" which work in very different ways but all pass the same signals to the PC.

A USB memory pen is another good example - essentially they all appear in exactly the same way but use different technology depending on the manufacturer and age of the pen drive. When you plug the device in, the operating system will load and configure the driver software and the pen drive will then appear as a new drive.

Driver software may need to be updated, either to fix any bugs, or to introduce new features. This can either be done automatically or when the user asks the operating system to check for any updates.

User Management

Most operating systems will allow user accounts to be created. Each user can have different settings such as desktop background, default colours and fonts, and can have their own user area. Accessibility features such as using a screen reader or reversing the mouse buttons can also be set to each user.

The operating system is responsible for managing these users and applying the correct settings to each account. Most user accounts will be unable to access work and documents created by other users, unless they have been explicitly given permission to access them.

The user accounts may be protected so that other users cannot log on as the wrong person. This may be done by using a password or PIN, but could also user a fingerprint reader or other biometric device.

File Management

Every computer system needs to be able to manage files, including programs and data files. The basic operations necessary include saving and loading files, renaming files, copying files, moving files and deleting files.

When you save a large number of files, it is very easy to lose them. Operating systems can organise the files by using "folders", or "labels" which allow you to add a contextual description to them. By using sensible, descriptive file names and folder names, it is much easier to keep track of every document.

Files can also have a "file type" associated with them, which allows a particular program or application to be used to "handle" them. One way of doing this is to use a "file extension" which is added to the file name. A document called "diary.docx" means that the document called "diary" has a file extension of ".docx" which is the default file extension for Microsoft Word.

The operating system may also encrypt the files to keep them more secure and could use compression techniques to reduce the file size without losing detail. This would allow more documents to be saved in the same sized file space.

Data is always at risk of being lost, either by failure of the hardware, or by the operator making an error that can lead to the data being over-written or deleted by mistake.

Keeping the data safe is very important, and regular backups should be performed. A backup utility will automate this process, and can be set to run automatically at set times. The backups may be stored on a removable storage device, or could be saved to a remote location, either on the network or even in an entirely different location.

A full backup is where every item is copied, regardless of whether another backup has already been made. This will produce very large backup files and may take many hours to complete.

Incremental backups will only back up any files that have recently changed. This will be much quicker, but has the disadvantage that it takes longer to fully restore files because each separate incremental backup must be restored in sequence.