Evolution of Operating System

1.Mainframe Systems

Reduce setup time by batching similar jobs Automatic job sequencing – automatically transfers control from one

job to another. First rudimentary

operating system. Resident monitor

•  initial control in monitor
•  control transfers to job
•  when a job completes control transfers pack to monitor

2. Batch Processing Operating System:

•  This type of OS accepts more than one jobs and these jobs are batched/ grouped together according to their similar requirements. 
• This is done by the computer operator.
•  Whenever the computer becomes available, the batched jobs are sent for execution and gradually the output is sent back to the user.
•  It allowed only one program at a time.
•  This OS is responsible for scheduling the jobs according to priority and the resource required.

3. Multiprogramming Operating System:

• This type of OS is used to execute more than one jobs simultaneously by a single processor. it increases CPU utilization by organizing jobs so that the CPU always has one job to execute.
•  The concept of multiprogramming is described as follows:

1. All the jobs that enter the system are stored in the job pool( in the disc). The operating system loads a set of jobs from job pool into main memory and begins to execute.
2.  During execution, the job may have to wait for some task, such as an I/O operation, to complete. In a multiprogramming system, the operating system simply switches to another job and executes. When that job needs to wait, the CPU is switched to another job, and so on.
3.  When the first job finishes waiting and it gets the CPU back.
4.  As long as at least one job needs to execute, the CPU is never idle.
5. Multiprogramming operating systems use the mechanism of job scheduling and CPU scheduling.

3. Time-Sharing/multitasking Operating Systems

Time-sharing (or multitasking) OS is a logical extension of multiprogramming. It provides extra facilities such as:

1.  Faster switching between multiple jobs to make processing faster.
2.  Allows multiple users to share the computer system simultaneously.
3.  The users can interact with each job while it is running.

These systems use a concept of virtual memory for effective utilization of memory space. Hence, in this OS, no jobs are discarded. Each one is executed using the virtual memory concept. It uses CPU scheduling, memory management, disk management, and security management. Examples: CTSS, MULTICS, CAL, UNIX,  etc.

4. Multiprocessor Operating Systems

Multiprocessor operating systems are also known as parallel OS or tightly coupled OS. Such operating systems have more than one processor in close communication that sharing the computer bus, the clock, and sometimes memory and peripheral devices. It executes multiple jobs at the same time and makes the processing faster.

Multiprocessor systems have three main advantages:

 Increased throughput: By increasing the number of processors, the system performs more work in less time. The speed-up ratio with N processors is less than N.

 The economy of scale: Multiprocessor systems can save more money than multiple single-processor systems because they can share peripherals, mass storage, and power supplies.

Increased reliability: If one processor fails to do its task, then each of the remaining processors must pick up a share of the work of the failed processor. The failure of one processor will not halt the system, only slow it down.

The ability to continue providing service proportional to the level of surviving hardware is called graceful degradation. Systems designed for graceful degradation are called fault-tolerant.

The multiprocessor operating systems are classified into two categories:

1. Symmetric multiprocessing system

2. Asymmetric multiprocessing system

•  In symmetric multiprocessing system, each processor runs an identical copy of the operating system, and these copies communicate with one another as needed.
•  In an asymmetric multiprocessing system, a processor is called master processor that controls other processors called the slave processor. Thus, it establishes a master-slave relationship. The master processor schedules the jobs and manages the memory for the entire system.

5. Distributed Operating Systems:

• In a distributed system, the different machines are connected in a network and each machine has its own processor and owns local memory.
• In this system, the operating systems on all the machines work together to manage the collective network resource.

 It can be classified into two categories:

1. Client-Server systems

2. Peer-to-Peer systems

Advantages of distributed systems.

 Resources Sharing

 Computation speed upload sharing

 Reliability

 Communications

 Requires networking infrastructure.

 Local area networks (LAN) or Wide area networks (WAN)

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6. Desktop Systems/Personal Computer Systems:

• The PC operating system is designed for maximizing user convenience and responsiveness. This system is neither multi-user nor multitasking.
•  These systems include PCs running Microsoft Windows and the Apple Macintosh. The MS-DOS operating system from Microsoft has been superseded by multiple flavors of Microsoft Windows and IBM has upgraded MS-DOS to the OS/2 multitasking system.
•  The Apple Macintosh operating system has been ported to more advanced hardware, and now includes new features such as virtual memory and multitasking.

7. Real-Time Operating Systems (RTOS):

•  A real-time operating system (RTOS) is a multitasking operating system intended for applications with fixed deadlines (real-time computing). 
• Such applications include some small embedded systems, automobile engine controllers, industrial robots, spacecraft, industrial control, and some large-scale computing systems.

 The real-time operating system can be classified into two categories:

1. hard real-time system and 2. soft real-time system.

• A hard real-time system guarantees that critical tasks be completed on time. This goal requires that all
• delays in the system be bounded, from the retrieval of stored data to the time that it takes the operating system to finish any request made of it. Such time constraints dictate the facilities that are available in hardreal-time systems.
•  A soft real-time system is a less restrictive type of real-time system. Here, a critical real-time task gets priority over other tasks and retains that priority until it completes. Soft real time system can be mixed with other types of systems. Due to less restriction, they are risky to use for industrial control and robotics