Operating Systems

An operating system is the software that runs the basic operations of your computer. Famous examples are Windows, Linux, OSX and Android.

You need to know some of the things an operating system does. Here they are:

• User Interface - two types. GUI - Graphical User Interface: has pictures on screen that you can click and drag e.g. Windows, Android. CLI - Command Line Interface: just a text entry screen and you have to know the commands e.g. CMD, Linux Bash.
• Memory Management - the operating system deals out the available memory to the programs running so that no two programs have the same spot and try to overwrite each other. If the computer runs out of RAM then it will allocate a part of the hard drive instead (virtual memory). Using virtual memory is much slower than using RAM.
• Peripheral Management - a peripheral is a device that plugs into your computer. The OS manages all keyboards, mice, scanners, microphones, etc. It does this using device drivers which are the software link between the peripheral and the OS.
• Multitasking - an OS lets you run more than one program at once. This is called multitasking. It does this by giving each task a slice of time with the processor and makes sure each task gets a fair share of processing time.
• Security - the OS helps to keep your PC safe with a Firewall and Anti-Virus.

Utility Software

Utility software helps to protect and maintain your PC. You need to know the purpose of these:

• Anti-virus - periodically scans your system looking for suspected malware. It compares programs against a known database of malware. If it suspects a program might be malicious it flags it and it can either be quarantined or deleted.
• Spyware protection - spyware tries to watch your keystrokes and PC activity so it can feed back information to a malicious person. Spyware protection attempts to prevent this.
• Firewall - checks all data coming into your computer to make sure it meets suitable criteria. This means it is likely to filter out viruses and other malicious programs.
• Disk formatter - prepares a disk for use by the computer. Useful for brand new disks. If you format an old disk then all the files are erased!
• File transfer - useful for transferring files. This is often used to transfer a file from a PC to a web server across the internet. Uses ftp (file transfer protocol)
• Disk defragmenter - when files are written to your hard disk they are often scattered all across the disk making performance slow. A defragmenter puts all related files together to speed up your drive and free up space.
• System information - gives you info about all the components inside your computer. This is useful for troubleshooting or finding suitable parts for upgrades.
• System diagnostic - scans your system looking for devices and drivers that are not functioning correctly. If any are found it tries to give you a solution e.g download update or report fault to manufacturer.
• System cleanup - makes space on your hard drive by deleting useless files. Files could include temporary files, temporary internet files, cookies, recycle bin, old registry entries.
• Automatic updates - goes to the website of your software manufacturer to see if there is a more up to date version of your software. If there is it downloads it and installs it. This can happen regularly e.g. daily or weekly.

Software Distribution

Software is distributed in a few different ways - both paid and free.

• Proprietary - you buy a license to use the software. The license will forbid you from copying, modying or distributing the software. You just get the finished compiled code - there is no source code so you can't make changes.
• Open source - this type of software is still licensed but the license is usually free and it normally allows copying, modyfying and distribution. You get the source code so you can make changes to customise it to your needs if you are a skilled programmer.


• Off-the-shelf - Software that is made for a huge mass market. You could probably go into PC World and pick it up "off the shelf". It will have a range of useful but general features. Something like Microsoft Office would fit into this category.
• Custom written - Software made especially for a purpose. Can have many special features at the request of the purchaser and could be very specialised. Usually expensive.

How images are stored

Bitmaps

A bitmap is a picture made up of tiny squares called pixels. The more pixels there are the more detailed the image and the higher the resolution. The computer stores a certain number of bits per pixel - this is called the colour depth. The higher the colour depth the more colours available.

The higher the resolution the larger the file size. The higher the colour depth the larger the file size.

Remind yourself about bitmap images with the Learn Computing Bitmap Creator.

Vectors

Vector images are stored differently to bitmaps. The computer stores the co-ordinates of a series of shapes together with attributes like width, height, fill colour, opacity and others.

Remind yourself about the types of attributes that make up a vector image with the Learn Computing Vector Creator.

How Sound is Stored

Sound is analogue. This means it needs to be turned into digital instructions so that the computer can work with it. When this happens it is called sampling.

The number of times per second that the sound is sampled is called the sampling rate. The higher the rate the better the quality but the larger the file size.

The amount of data taken with each sample is called the sampling depth and is measured in bits. The higher the sampling depth the higher the quality but the larger the file size.