I dealt with computers first when I was in the elementary school around 1998, where I used to play Sky Roads on DOS computers. 2000 was the year I convinced my father to buy a computer at home, Some guy came at home and installed Windows so that we can deal with the computer, This Windows was like a mysterious thing or like a ghost that controls my PC, Actually I didn’t pay attention to know what Windows is all about rather than it is a kind of “Operating System” ! but as an end-user I was very good at using it.

Now as a computer science student, I figured out what Operating System – abbreviated OS – is all about, this article intend to give a brief overview to Operating Systems.

What is OS?

• A program that controls the execution of application programs, and act as an interface between the application and the computer hardware.
• It has 3 objectives:
  • Convenience; makes computer more convenient to use.
  • Efficiency; allows us to use computer resources in an efficient manner.
  • Ability to evolve; allow for further development to allow to system functions.

OS as a user/computer interface

• OS provides a variety of services in the following areas:
1. Program development: editors, debuggers they are tools supplied with the OS.
2. Program execution: automate a number of steps to execute a program.
3. Access to I/O devices: act as a façade to I/O devices.
4. Controlled access to files: provide protection mechanism to control access to files.
5. System access: protect system data and resources from unauthorized users.
6. Error detection and response: detect program and hardware errors so as to clear the error condition with the least impact on the running applications.
7. Accounting: monitoring system resources and collect usage statistics, help in judging whether to upgrade the resources or it is efficient enough.

OS as a Resource Manager

• Memory allocation is controlled by the OS and the MMU (Memory Management Unit).
• The OS decides when I/O device can be used by a program in execution.
• Control access to and use of files.
• The processor operation itself is controlled by the OS, that OS decides how much time the processor can spend on a particular program.

What makes OS evolve ?

1. Hardware upgrades and new types of hardware: New types of hardware require that the OS be able to deal with it, so OS should be built with support for that hardware.
2. New services: OS offers new services demanded by the users or system managers.
3. Bug Fixes: Bugs appear over time, and detected by users, so OS should be fixed for this bugs, and sometimes fixing a bug raise another bug.

OS Evolution

In the dark ages, when there was no OS from late 1940s to mid-1950s (I call this years: before OS, abbreviated BOS like BC) the programmer had to deal directly with the computer hardware, These computers were run from a console consisting of display lights, toggle switches, some form of input device.

• Serial Processing:

• This systems presented two main problems
  1. Scheduling: users had to sign-up sheet to reserve computer time, users couldn’t`t know precisely how long it will take to finish their program.
  2. Setup time: A single program called a job had to be installed before used with its compiler and code, saving the object program and linking and so on to run the program.
• Users have access to computer in series.
• Simple Batch Systems
• Monitor: a software program that handle executing the jobs provided by the user on tapes or disks.

• Multiprogrammed Batch Systems

• The I/O devices are much slower than the processor, leaving the processor idle most of the time waiting for the I/O devices to finish their operations.
• Uniprogramming: the processor starts executing a certain program and when it reaches an I/O instructions, it must wait until that I/O instructions is fully executed before proceeding.
• Multiprogramming: in contrast to the uniprogramming, when a job needs to wait for an I/O instruction, the processor switches to another job executing it until the first job finishes its waiting I/O instructions, the processor continue to swap between jobs as it reaches an I/O operation.
• Multiprogramming batch system must rely on certain hardware capabilities such as process switching when swapping between program execution.
• Interrupt-driven I/O or DMA helps a lot in multiprogramming environments, allowing the processor to issues an I/O command and proceed executing another program.

• Time-Sharing Systems

• As multiprogramming allows processor to handle multiple batch jobs at time, it can allow the processor to handle multiple interactive jobs at time, through time sharing.
• Time Slicing: there is a system clock that generates interrupts at a constant rate, allowing the OS regain control and assign the processor to another process.

Time sharing and multiprogramming raise a host for new problems

• If multiple jobs are in memory they must be protected from interfering with each other.
• File systems must be protected from access by unauthorized users.
• The programs contention for resources (mass storage, printer, … ) must be handled by the OS.

Major Achievements in OS

• The Process
  • Possible Definitions:
    • A program in execution.
    • An instance of a program running on a computer.
  • The interrupt helped programmers in developing early multiprogramming and multiuser interactive systems.
  • Errors caused by handling more than one process at time is:
  1. 1. Improper synchronization
     2. Failed mutual exclusion: allow only one routine at a time to perform an update against the file.
     3. Non-determinate program operation: programs may interfere with each other when they share memory and their process is interleaved by the processor.
     4. Deadlocks: 2 programs hung up waiting for each others to release a resource.
  • The execution context or the process state is the internal data by which the OS is able to control the process.
  • The context contains the content of the processor registers, as with information to use by the OS as the priority of the process.
• Memory Management
  • Process Isolation: OS should prevent independent processes from interfering with each other.
  • Automatic allocation and management: Programs should be dynamically allocated, and allocation should be transparent to the programmer.
  • Support of modular programming: Programmers should be able to write their own programs and create, destroy and alter the size of it dynamically.
  • Long-term storage: saving information for extended periods of time.
  • Protection and access control.
• Information Protection and Security
  • the use of time-sharing systems, computer networks has brought concern for the protection of information.
  • We are concerned with the problem of controlling access to the computer system.
  • Work in this area can be grouped in:
    • Availability: protect the system against interruption.
    • Confidentiality: users cannot read data for which access is unauthorized.
    • Data integrity: protection of data from unauthorized modification.
    • Authenticity: verification of the identity of the users and validity messages.
• Scheduling and Resource Management
  • Any resource allocation and scheduling policy must consider:
    1. Fairness: jobs of the same class competing for a resource are to be given equal and fair access to that resource.
    2. Differential responsiveness.
    3. Efficiency: OS should maximize processor utilization, minimize response time, and accommodate as many users as possible.
  • OS elements involved in the scheduling of process and the allocation of resources in a multiprogramming environment:
    • Short-term queue: contains processes in the main memory and are ready to run as soon as the processor is made available.
    • Short-term scheduler: decides which process in the short-term queue to use the processor, a common strategy is to give each process some time in term (round-ribbon) technique.
    • Long-term queue: list of all new jobs waiting to use the processor, the OS adds jobs to the system by transferring process from the long-term queue to the short-term queue.
    • I/O queues: each device has a queue for the processes waiting to use that device; it is the OS that decide which process to assign to an available I/O device.

References

What is batch system?

In early days computer work was given on punch cards and then these punch cards behave as input to the computer. These jobs or batch jobs were then executed by the computer one by one. So that computers were called as batch computers or batch systems. The work done by batch systems are in parts i.e. one job is processed then another job in the queue is processed and so on. T25 download free.

Why batch systems are used?

As batch systems load less stress on processor and involve less user interaction so that is why we can use batch system in current days also. Another advantage of batch systems is that the large repeated jobs are given to the system and we don’t have to interact with computer to tell the system that you have to do that job after finishing that job. Old batch systems were not interactive i.e. the user interaction was not involved when the job is running. Now in modern batch systems we have interactions also. For example we can set the timer on the job and when the specific time comes then computer send message to the processor that time is over. This helps us to avoid too many errors and makes us easy to debug.

Best practice in using batch systems

The batch systems are used by large organizations and also large jobs are done in sequence by the system. So it is best practice to divide the big job into small parts and run them so it is easy to debug the job when error comes. You can also set timer on computer for each job so you can check and interact with job to check and debug errors. Yakuza ishin english patch.

Advantages of batch processing systems

Here are some advantages of batch systems:-

• Repeated jobs are done fast in batch systems without user interaction.
• You don’t need special hardware and system support to input data in batch systems.
• Best for large organizations but small organizations can also benefit from it.
• Batch systems can work offline so it makes less stress on processor.
• Processor consumes good time while processing that mean it knows which job to process next. In real time systems we don’t have expectation time of how long the job is and what is estimated time to complete it. But in batch systems the processor knows how long the job is as it is queued.
• Sharing of batch system for multiple users.
• The idle time batch system is very less.
• You can assign specific time for the batch jobs so when the computer is idle it starts processing the batch jobs i.e. at night or any free time.
• The batch systems can manage large repeated work easily.

Disadvantages of batch processing systems

• Computer operators must be trained for using batch systems.
• It is difficult to debug batch systems.
• Batch systems are sometime costly.
• If some job takes too much time i.e. if error occurs in job then other jobs will wait for unknown time.

Examples of batch systems

1.Payroll system

Batch systems are ideal for making payrolls. The salaries of employees can be printed at the end of month by the batch systems. Keygen logitrace v12 bus. So the statements can be made easy by using batch systems.

2.Bank statements

At the end of month the bank makes statements for each account holder. So these bank statements can be made easily by batch systems at the end of month.