Operating systems

Operating systems

1. Role

   • It is the system software and its job is to hide the complexities of the hardware to the user. It also manages the hardware resources to provide and orderly and controlled allocation of the: processor, memory and I/O Devices. Manages and controls the applications.
     • Hiding the complexity- The user to a computer doesnt need to actually know what is going on all they need to be able to do is click on icons and navigate through menus and then the OS does what it needs to. All of the screens shown by the OS, the input and outputs and the menus and icons are all represented by the User Interface. These can be in different forms:menu driven, form based, GUI;windows, icons, menus, command lines and natural languages
     • Controlling and Managing Applications- A PC only has one CPU but you can run multiple applications at once, or so it seems. What the CPU actually does is it works on one application for a certain amount of time and then moves onto the next one and then the next and then comes back and work on the first again. As it flicks between applications so quick it appears that it is doing them at the same time. The OS must also: launch applications, manage applications, flick between applications and manage the I/O Devices.
     • Memory Management- When an application is run the OS finds it in the backup memory and then loads it into RAM in the same way that the OS itself is loaded into RAM. Where in memory the application is placed is down to the OS they need to be placed where they wont interferewith each other or the OS itself.
     • Data Storage Management- When a user wants to save a document they select the drive for it to be saved on and then select appropriate folders and give it a name. It is the OS's job to decide exactly where on the drive that it is saved. The OS keeps a log of where all of the folders are saved by creating a table on each drive with the locations of the folders.

2. It must be loaded into RAM before use. Examples of where they are used is in:pc's, mobile phones, calculators and cars.

3. Classification

   • Interactive OS-Is where the user directly interacts with the OS. The user creates a request using the user interface and sends it to the OS and the OS replies straight away. The time is seen as negligible, a dialogue goes on between the user and the OS hence dialogue boxes.
   • Non-Interactive/Batch processing OS-Is where the user creates a request, in this situation called a job, and sends it to the OS. This job is then placed in a queue to be processed by the OS later. All communications are off line and everything sent must be checked for any errors.

4. Type

   • Real Time-This receives input and then processors the input to create the output and then gives feedback on the output before the next input is received. The output is generated immediately. An example is a ticket booking system as tickets can only be booked that are available so the last output effects the next input.
   • Network-Computer systems designed to allow users to share data and resources at, apparently, the same time.
     • Peer to peer- This is when all the computers on the network have the same rights to access the data. This means that no one computer is in charge and software is needed to allow all the computers to share data. Advantages are that it is easy to setup and that there is less hardware needed as there is no need for a server. Disadvantages are that there is not one central location for storage and it is less secure than client and server.
     • Client to Server- All the computers connected to the network are called clients and then a powerful computer is called the server and this stores all the files, function, applications and security. Advantages are that servers are more stable, the security can be provided through the server, the server can be accessed remotely from any location by any system and that it is easier to integrate new software and hardware into the network. Disadvantages are that the server requires regular maintenance and updates, it is costly to setup and maintain a server and that all the clients are dependent on one central location.
       • Proxy Server- Is a server, computer system or application that acts as an intermediate when one computer wants to access data from another computer or server. The client connects to the proxy server sends their request, for a file or web page, the proxy server then evaluates the request in order to simplify it and then forwards it on to the other server. Its purposes are to: keep machines behind it autonomous for security, to prevent the download of the same thing multiple times and save bandwidth, scn transmitted content for malware before delivery, scan outgoing messages for data loss prevention and speed up access to resources
   • Device-These are OS on devices such as mobiles and tablets. They are made for the hardware platform but all offer similar things such as: HCI, GUI, Communications and application management.
   • Embedded-These are on computer systems that have a limited or no user interface. They work fully or largely autonomously within other machinery. Firmware is used to describe the OS that manages the embedded device. They are used in cars and microwaves.
   • Desktop-These allow the user to do a wide range of general purpose tasks and it is what we are most familiar with in Windows. For example GUI, file management and launching applications.
   • Server- Provide specific services to all their networked clients. A network cannot work without a Server OS and it sits under the Network OS. Examples are Web servers, Proxy servers, FTP servers and on-line gaming servers.

5. Managing Hardware

   • I/O Devices- When an I/O device is connected to the computer it is the OS it communicates with. To do this drivers have to be downloaded. A driver is a piece of software that allows the successful communication and operation between the device and the OS.
     • Interrupts- When there is an error with the I/O device the I/O controller creates an interrupt and sends it to the OS. As the interrupt needs dealing with straight away the OS stops what its doing and deals with the interrupt.
   • OS's can come with utilities which are small programs that deal with specific tasks that are common among users. Examples in Windows are DEFRAG and SCANDISK.

6. Security and Access

   • Authentication- Is proving you are who you say you are and is split into two parts. The first is accepting proof of identity like a username or retina scanner and is seen as what the user is or does. The second is comparing what the user says to what is know of the user like a password or security question and is seen as what the user knows. Examples of authentication is capthca or an email back when changing password.
   • Authorisation- Is you are permitted to do what you are trying to do and in computing terms means giving control to certain parts of the system. Access rights to parts of the system is when the users to the system are split into groups such as students and teachers at a College and then the groups are given access and rights to the resources. Access rights to individual resources is when only certain users have rights to a resource so it is given further authentication like a password.
   • Accounting- Is the keeping of logs to record the activity on a system. Logs and audit trails are important in detecting and recreating security breaches. The logs need to be reviewed and maintained in order to be passed as sufficient evidence. A clipping level is when the system can generate automatic reports based on certain criteria. For example is a login is failed three times in a row or if somebody tries to access a disabled account. They are important to identify possible break in attempts.
   • Firewall- Is software or hardware that monitors incoming or outgoing packets and decides whether or not they are allowed to pass through based on rules already set by the organisation. Once the other network, usually an external network like the internet, is seen as secure and trusted the firewall will build a bridge between the network or computer it is protecting. It builds a bridge against a network that is not usually trusted.