Batch Systems :
Batch means group. Batch systems were introduced to reduce the computer’s CPU idle waiting time for the operator to ask it to do something or waiting for other tasks to finish. To overcome this, the jobs that the computer was being asked to do were submitted in batches.
A batch process performs a list of commands in sequence. It be run by a computer’s operating system a script or batch file, or may be executed within a program using a macro or internal scripting tool. For example, an accountant may create a script to open several financial programs at once, saving him the hassle of opening each program individually. This type of batch process would be executed by the operating system, such as Windows or the Mac OS.
Multi-programming Systems :
Multi-programming is a method of operating such that several programs appear to be running at once.
The jobs are usually given priorities. The operating system switches jobs in and out of processor time according to priority. For example, while one job is being allocated printer time, another will be being processed in memory. The processor is so fast that it seems that many jobs are being processed at the same time.
In multi-programming systems, the running task keeps running until it performs an operation that requires waiting for an external event (e.g. reading from a tape) or until the computer’s scheduler forcibly swaps the running task out of the CPU. Multi-programming systems are designed to maximize CPU usage.
CPU Scheduling :
CPU scheduling is a process which allows one process to use the CPU while the execution of another process is on hold (in waiting state) due to unavailability of any resource like I/O etc, thereby making full use of CPU. The aim of CPU scheduling is to make the system efficient, fast and fair.
- Allocation of devices:
Means peripheral devices allocation or allocate for different jobs.
Time-Sharing System – Interactive Computing :
An operating system feature allowing several users to run several tasks concurrently on one processor or in parallel on many processors, usually providing each user with his own terminal for input and output. Time-sharing is multi-user multitasking.
- A job swapped in and out of memory to the disk. Each user has at least one separate program in memory. To obtain a reasonable response time, jobs may have to be swapped in and out of main memory.
- On-line communication (or Interaction) between the user and the system is provided, when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.
- On-line system must be available for users to access data and code.
Desktop System :
A desktop is a personal computer designed for regular use at a single location on or near a desk or table due to its size and power requirements.
- Personal computers – computer system dedicated to a single user.
- I/O devices – keyboards, mice, display screens, small printers.
- User convenience and responsiveness.
- Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features.
- May run several different types of operating systems (Windows, MacOS, UNIX, Linux)
Multiprocessor System :
Multiprocessing is a type of processing in which two or more processors work together to process more than program simultaneously. It allows the system to do work in a shorter period of time. UNIX is one of the most widely used multiprocessing systems. Multiprocessor system is also known as parallel system or tightly coupled system. It means that multiple processors are tied together in some manner.
Advantages of Parallel System:
- Throughput: An increase in the number of processes completes the work in less time.
- Reduced Cost/Economical: Multiple processor share same resources. Separate power supply or motherboard for each chip is not required this reduces the cost.
- Reliability: The reliability of system is also increased the failure of one processor does not affect other processors though it will slow down the machine.
Symmetric Multiprocessing (SMP) :
Symmetric multiprocessing (SMP) is the processing of programs by multiple processors that share a common operation system and memory. In symmetric (or “tightly coupled”) multiprocessing the processors share memory and the I/O bus or data path. A single copy of the operating system is in charge of all the processor.
- Each processor runs an identical copy of the operating system.
- Many processors can run at once without performance deterioration.
- Most modern operating system support SMP.
Asymmetric Multiprocessing :
Asymmetric multiprocessing (AMP) was the only method for handling multiple CPU, before symmetric multiprocessing (SMP) was available. It has also been used to provide less expensive options on systems where SMP was available.
- Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.
- More common in extremely large systems.
Distributed Systems :
Distributed system is a collection of computers that act, work, and appear as one large computer. There are several distributed computing projects on the Internet that help work on complex problems by sharing the processing power of millions of different peoples computers. To participate and help these programs, often you only need to download a small program that is run whenever your computer is not being used. Below is a listing of some of these programs.
A distributed computer system consists of multiple software components that are on multiple computers, but run as a single system. The computers that are in a distributed system can be physically close together and connected by a local network, or they can be geographically distant and connected by a wide area network. A distributed system can consist of any number of possible configurations, such as mainframes, personal computers, workstations, minicomputers, and so on. The goal of distributed computing is to make such a network work as a single computer.
Loosely Coupled System :
Each processor has its own local memory; processors communicate with one another through various communication lines, such as high-speed buses of telephone lines.
Advantages of Distributed Systems :
- Resources sharing: means online sharing memory or RAM.
- Computation speed up – load sharing
- Reliability
- Communication
Distributed System (Cont.) :
- Require networking infrastructure.
- Local area network (LAN), Bluetooth device communication, metropolitan area network (MAN) or wide area network (WAN).
- May be either client-server or peer-to-peer systems(like university network).
Clustered System :
A computer cluster consists of a set of loosely or tightly connected computers that work together so that, in many respects, they can be viewed as a single system. Unlike grid computers, computer clustershave each node set to perform the same task, controlled and scheduled by software.
Essentially, many many computers hooked up together to do lots of processing work. You will mostly always find clustered systems in IT offices, research laboratories.
- Clustering allows two or more systems to share storage (linked via LAN networking).
- Provides high reliability & availability.
- Asymmetric clustering: one server runs the application while other servers standby.
- Symmetric clustering: all N hosts are running the application
Real-Time System :
A real-time system is a type of hardware or software that operates with a time constraint.
Definition:
A real time system is a system that ensures the exact time requirements for a job. If a real time system does not complete a task in certain time it may cause a breakdown of the entire system it is running .Some applications required to be serviced within a time period.
(1)Industrial control system, (2) Automobiles break, (3) Airline guidance, (4) Medical devices.
- Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.
- Well-defined fixed-time constraints.
- Real-Time systems may be either hard or soft real-time.
Real-Time Systems (Cont.):
Hard real-time:
- Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM)
- Conflicts with time-sharing systems, not supported by general-purpose operating systems.
Soft real-time:
- Limited utility in industrial control of robotics
- Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.
Single user system :
A computer system that allows only one user to use the computer at a given time is known as single user system.They may run different types of operating system, including Dos ,Window and Mac operating system. In single user system the system may permit only one program to be active at a given time.
Multi user system :
A computer system that allows multiple user to use the computer at a given time is known as multi user system. They may run different types of operating system including UNIX, LINUX etc. The operating system for multi-user system maintain more than one programs in main memory simultaneously to perform effective sharing of cpu time the storage space and other resources among the active programs.
Handheld Systems :
A handheld computer is a computer that can conveniently be stored in a pocket (of sufficient size) and used while you’re holding it. Today’s handheld computers, which are also called personal digital assistants (PDAs), can be divided into those that accept handwriting as input and those with small keyboards.
A mobile device is a small computing device, typically small enough to be handheld (and hence also commonly known as a handheld computer or simply handheld) having a display screen with touch input and/or a miniature keyboard and weighing less than 2 pounds (0.91 kg).
Issues:
- Limited memory.
- Slow processors.
- Small display screens.
Computing Environments :
- Traditional computing
- Web-Based Computing such as windows ME (handhelds, PDA, cellphones,…)
- Embedded Computing (embedded real-time OS, car engines, VCR, microwave ovens,…)