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Operating Systems Essay Sample

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Operating Systems Essay Sample

1. Identify and fully describe the main developments of Operating Systems, giving examples of their origins and use.

Batch Operating Systems were an early operating system available, and were first introduced in the mid 50’s. They were designed to make human manual work easier; humans were replicating identical jobs over and over again, hence in batch.

A batch operating system keeps itself eventful; it does this by taking jobs from a batch queue, instead of waiting for people to submit jobs. The jobs are then processed one or more at a time under control of the operating system, however most jobs undertaken in this operating system would be single-task.

These type of operating system were often left to work overnight, mainly because the jobs were ‘batched’ the next job in the queue would be commenced as soon as the previous job had been completed, this way of processing would allow for a large work load to be automatically completed without the requirement to wait and tell the computer to do the next job.

Real Time Operating Systems (RTOS) are often embedded, meaning a integral part of a system inside another device.

They have very little user interface capability.

Real time operating systems like their name implies, respond to an input immediately.

“Real time operating systems are capable of processing data so quickly that the results are available to influence the activity currently taking place.”

[Computer Science 5th Edition, CS French, Ashford Press Gosport, 1996]

Real time operating systems guarantee a certain capability within a specified time constraint; these time constraints are usually very rigid. If the system does not conform to this time limit, the system ultimately fails.

They are used for various purposes; a few of these are medical equipment, industrial control systems and car computers.

Parallel Systems have more than one processor to carry out a single job.

The systems often carry out one single job using the resources of both processors of the machine; however some systems will have a processor dedicated to a single task. These operations work in parallel (side by side) of one another.

Distributed Systems act as an illusion to a user. A multiple number of nodes are set up on a network, to allow data access or device sharing. This allows for other users of different machines to access data on another machine on the network.

For example at college a student logs on to the machine, the machine seems local to the user, the user observes the system as using its own local drives and devices. However these

Drives and devices are setup on a client-server machine but appear to be local to the user.

Time Sharing Operating Systems allow multi-tasking, the operating system shares a slice of the processor resources to designated programs and users logged on to the system.

For example, it is not unusual for a home user to have a word processing package, internet browser and a multimedia package to be open at the same time. Microsoft Windows is a great example for allowing this.

Personal Computer Operating Systems were brought about in the early 70’s.

However it wasn’t until the 1980’s that they became popular, and the focus of the operating system changed from the hardware aspect, to that of the user interface (how the user observes the operating system).

Personal Computer Systems are simply operating systems that share the processors resources for single user’s tasks.

The main concept behind personal computer operating systems is the user interface. The workings are important; however the main principal is that the user is entirely interactive with the system.

These are perhaps the most difficult for designers to produce, as a very high level knowledge of user interface design is required. This is to allow users of any level to use the system comfortably.

It allows for considerable power for a single user to run high-tech graphics and multimedia packages. These operating systems evolved in to very capable systems, allowing for heavy multi-tasking usage.

Examples of Personal Computer operating systems are as follows:

Microsoft Windows


Apple Macintosh MAC OS

2. Identify and fully describe the main purposes of an operating system. All components of the operating system are required to be covered, to clearly show an understanding of what each component does and how they ‘fit’ into the overall system design.

Process Management

Process management is a way of tracking processes and managing them in such a way that there is enough processor resources to correctly function.

Process is another word for a task that is to be performed by the computer. Along with a process is a set of information about the particular process.

The information required to track these processes are stored in a data package called a ‘Process Control Block (PCB).

The process control block contains the following information about a process:

* An identification number that uniquely identifies the process

* Owner ID – An identification of the user/device who the process belongs to

* Priority – A number to represent its priority to the system

* Status – What its current state is. This is 1 of 3 states (Ready, Waiting, Running)

* Units of Processor Time Used

* Resources waiting for – for example paper for the printer.

* Link to Another PCB –

* Registers – the registers the process has contents in.

Process ID


Owner ID

Chris. Oliver





Units of Processor Time Used


Resource waiting for

Disks [printer]

Link to another PCB

Next PCB in wait Queue


Contents of registers when process last stopped running

An example of a PCB is shown below: this is for a print job

A Processes state is diagrammatically shown below, this shows state transition and how it works.

A process can be in one of five states; these five states are as follows:




A process’s state at the beginning, this is when the devices and memory allocation size is decided.


this state is when the process has been allocated all the resources required and is ready for being operated on by the computer


This state is when the process is in the CPU


This is when the process stops because of an input or output waiting to be completed. The process is removed from the processor and is allocated this state. It is given this state until the input or output is given the all clear.


This is when the process has been finished, and all the devices used by the process have been released ready for the next process.


Deadlocks occur when a multiple number of processes fight for very little resources available from the processor.

For example one process has been granted the allocation of the modem, however is waiting for a text file, but process two has the text file and is waiting for the modem. In this instance each process will not gather the resources required because they have been allocated to another process, this is where a deadlock occurs.

Process Management in an operating system has the job to destroy one of the processes to allow for one of the processes to be put in the ‘ready’ queue.


Scheduling is a method in the operating system that allows processes to enter the ready queue allowing them to then take execution.

The strategies used to take these processes and allow them to be ready for execution are as follows:

* Process the maximum amount of jobs.

* Sharing out processing time equally to users

* Providing acceptable response times, this is in the form of not running intensive programs while users are logged on to the system.

* Keeping devices as busy as possible.

* Attempting to gradually freeing up of processes, instead of crashing.

* Avoid Deadlocking

Scheduling is comprised of three sections:

1 – Long Term Scheduling – this is where processes are batched together, when the resources and space are free the process is then executed. This type of scheduling is used for jobs like heavy overnight print jobs.

2 – Mid-Term Scheduling – this is where a decision is made as to whether the processor is to busy for the amount of processes attempting to use it, the decision can be then fixed by terminating processes. When the system is free again the process can be re-executed.

3 – Short Term Scheduling is a where the next process is selected from the ready queue; it uses algorithms to do this.

Shortest burst time – being the time spent running before the process will have to wait before an input or output operation.

Shortest remaining time is the processes that have very little time left; this inevitably allows space for another process to execute.

Priority scheduling – a control that allow special circumstance processes to execute through the system quickly.

Round robin – limits the time a process is allowed to run before it is removed, it is then placed back in the ready queue.

Memory Management

Memory is an area in which data and instructions are stored. These operations must be managed by an operating system in order for the system to be stable and to run fluently.

Memory management within an operating system must ensure that a process has enough memory to run, ensuring it does not go in to another processes slot as this causes corruption. This management is a way of protecting memory from becoming unstable.

Memory management is also responsible for using the computers other memory sources effectively, to ensure programs run smoothly and effectively.

This is handled by using virtual memory; using the hard disc drive as a temporary memory source for processes and data.

This can benefit the user in various ways:

– The user is not rigidly restricted to space available. Using a large virtual memory space provides convenience for instances where large programs etc. are required to be stored in memory.

– Users are using less physical memory; therefore the system can handle more users on the system.

High Speed Cache is a fast memory storage; cache predicts the data that the CPU may need next, it then retrieves it from RAM and places it in to the high speed cache, this speeds up system performance, as cache is a lot faster than RAM is in providing for the processor.

The operating systems task is to control an even flow of the processes and decide where they should go practically, moving processes to the best location as the scheduler asks it to do so. This scheduler knows what process is next in line therefore can tell memory it is next and to move it to a suitable location for it to be quickly accessed.


Paging is a method used in operating systems to make a program’s memory non-contiguous, in simple terms; allowing a program to be allocated to any memory location available.

This is used when a bulk of data is bigger than the memory allocation it has been given; it firstly fills the memory allocation provided, and then stores the rest of the data in any space available in memory. This method of splitting the data is known as ‘Fragmentation’.

This decreases system performance.


To enhance the performance of the memory of a secondary storage medium, the operating system runs an operation called ‘Defragmentation’.

Defragmentation is a process that sorts data in to a contiguous sequence. If a non-contiguous set of data is found, it will be relocated and stored as a whole.

The image above is an illustration to show pictorially how a storage device could look in a data structure.

As you can see fragmented files are scattered. If this data was attempted to be retrieved it would be slower feedback to the user as the data has been fragmented and would have to be found first.

If data is to be found quickly and retrieved without a problem, the diagram below shows how a data structure should pictorially look. The image shows a contiguous data structure, with no fragmented files. This is the idea state for a system to be operated under.

File and Disk Management


CONTIGIOUS – Blocks of data are assigned in a complete row, using this method the files are simple to access.

The space must be large enough to store all the data

Files may become larger, therefore the space may be too small in the future, then it will need relocating (moved)

This then causes fragmentation of the storage device.


Files are recognised by operating systems and worked upon by using file extensions.

A file consist of two parts, one being the unique name to the user, second being the file extension related to the program that runs that type of file.

The operating system recognises exactly which program to open when the file is run.

The way that files and data are managed, is critical to the performance of the computer and the security of the data.

File management within an operating system provides a logical way for the user to observe there data, instead of having the complication of the physical implementation.

Operating systems main job in this area is to ensure that data is stored and relocated correctly, as well as having the responsibility to process files, find space to store them, and to retrieve this data at any time.

For example a .PDF file when run will be recognised by the operating system to be open in Adobe Acrobat Reader, providing the program is installed on the computer.

An operating system can perform several different tasks towards files, they are as follows:




finding space for it on storage medium, a new record made in directory


Finds the file from directory and adds data to it.


Finds the file then puts it in to memory and a read pointer is used to track where the next read place is to take place. In most operating systems however, a write pointer is held at this point, in-case the user intends to write to the file while reading


finds the file, then frees all space given to it, this is then erased from the computer

Files are a collection of saved information that is stored on a type of storage medium for later retrieval.

File attributes are the information related to the file, just like we have information related to ourselves, i.e. telephone number and home address.

A files attributes are vital in order for the operating system to create a file structure system, it does this by using the attributes to sort the files in to some kind of order.

For computer data files there are a set of minimum attributes related to them, they are as follows:

Attribute Name



an identifier to the user, in the form of a string of characters


the type of file it is, this is important as different operating systems handle different types of files differently.


Information held about where the file is stored, usually in the form of a path to it.

e.g. C:\Documents and Settings\Chris\Assignment.doc.


The size of the file (in bytes) e.g. 270kb.


Permissions to who can access the file. I.e. Read Only


when the file was created, modified or accessed.


the person the file was created and saved by.


Directories are a hierarchical way of separating these files; directories simply make it simpler for users to relocate the file at another time.

The root is the top directory of a file system; the root is determined by the operating system.

The root directory is usually the bootable device on a home computer system. Commonly C:

Paths are a list of directories that the operating system goes through to find a run able file. For example: C:\windows\cdplayer.exe

The operating system will go in to the ‘root’ and then in to the directory ‘Windows’ the file named ‘cdplayer.exe’ will then be located and executed.

Tree Structure – are of a hierarchical nature, therefore the top level is the root of the directory and every other sub directory from which all other directories stem off.

A Backslash is used to separate and indicate directories within directories (sub directories)

Directories allow a method for the operating system to easy locate files.

Volumes are a fixed amount of storage space allocated on a device. If a hard disc drive has two partitions set up, then it is said to have ‘two’ volumes because it has two separate fixed storage spaces.

Formatting a device in turn means to prepare it for read and write access. It does this by wiping all drive information that has been pre-set, it then tests each sector of the disc to ensure they are reliable enough for read and writing in and out of.

File Allocation Techniques

FAT (File Allocation Table) 32

Located on the storage device, basically holds the relevant information in a table, to find the data on the disk. its security does not measure up to that of NTFS and its filename size constraint is poor to that of NTFS.

Searches from top to bottom when looking for a file.

Contains the first block of each file on the disk,

Requires a tremendous amount of space

NTFS (New Technology File System)

Used in Windows NT based operating systems

Uses a similar table to that of FAT32 to keep track of file locations

Looks at directory structure from the side to help speed up the location of files

Uses Link Listed Allocation.

Linked allocation creates inked lists using disk sectors as nodes. For example, if the sector size is 512 bytes, and it takes a 32 bit number to represent the next block address, then only 508 bytes can be used to store data (the other 4 bytes are used to locate the next file sector).

This approach eliminates external fragmentation (since even the smallest block can now be used).

Some problems with this approach are that seeking within a file is now difficult. For example, if we’re interested in the last 100 bytes of a 100mb file, we need to traverse all the sectors of the file (follow links) to get to the last 100 bytes.

Another major issue is that we need to do a disk seek with every disk sector (unless disk sectors are contiguous).

And yet another issue with this is that storing pointers on every disk sector uses up a lot of disk space.


Used I-Nodes – an indexed file allocation method.

Its fast for small blocks of data and can accommodate extremely large volumes of data

RAM Disk

RAM disks are a temporary storage solution, data cannot be permanently saved, and data is lost on any type of system shut off. I.e. system reboots.

A Random Access Memory disk is a segment of the main memory that is left for extra storage if required. This is otherwise known as a ‘Virtual Drive’.

The main use for this area is that of performing operations to files, this is a better way of performing operations as the rate at which they can be performed on are that much higher than that of a physical drive.

Size constraints are a major problem with RAM disks, as they are limited to that only of the RAM contained in the machine. For example in modern home computer systems 256mb of RAM is contained, therefore only 256megabyte of RAM disc can be used. 256mb in today’s computing is very little in comparison to what users require.

OS Services – files, copy, delete, rename, view, find, backup

Directories – create, rename, list, delete

Programming, Open, close, read, write, seek

File allocation methods, FAT 32, NTFS, UNIX,

Disk caching

RAM disk


I/O System Management


DMA takes control of the system by imitating the processor; it does this to enable itself to transfer data to and from the memory using the system bus.

Buffering is required primarily because of the slow nature of I/O Device function.

It is a way of smoothing out an I/O operation,

Virtual Segmentation –

each process is divided in to slices (segments)


Caching and Spooling of Input and output devices


System Components ( CPU, RAM, System Bus, Local Buses, Device Controllers, Control Registers, Devices).

IO response System (polling, interrupts, I/O, DMA

Kernal Layers, Purpose, Device, Drivers, System calls

Device Management

Device management controls hardware resources; this includes the control over selection and operation of the devices used for input, output or storage.


Select an appropriate type of operating system for the following ICT needs, giving the choice of current operating systems [trade names]:

a) Local council office department in charge of the collection, and distribution of council tax.

b) A national car-rental agency, whose main computing centre is located in Sheffield, through which all of the daily transactions for the business are conducted.

c) An electro-plating circuit board manufactures.

d) A travelling company representative, who uses technology to keep in touch with his office.

3. Research and identify the different operating systems currently available for desktop computers. From your research and investigations of these operating systems you must critically evaluate them. This evaluation should clearly demonstrate your understanding of the differences found including and potential disadvantages.








[Computer Science 5th Edition, CS French, Ashford Press Gosport, 1996]

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