OPERATING SYSTEM
WHAT IS AN OPERATING SYSTEM?
INTRODUCTION OF OPERATING SYSTEM (OS)
“An operating System (OS) is an intermediary between users and computer hardware. It provides users an environment in which a user can execute programs conveniently and efficiently.”
• Without a brain, we are not able to do anything at all. An operating system is the brain of a computer.
• In technical terms, it is software which manages hardware. An operating system controls the allocation of resources and services such as memory, processors, devices and information.
• A computer system can be divided into four components:
the hardware,
the operating system,
the application software,
and the users as shown in figure.
• In technical terms, it is software which manages hardware. An operating system controls the allocation of resources and services such as memory, processors, devices and information.
• A computer system can be divided into four components:
the hardware,
the operating system,
the application software,
and the users as shown in figure.
DIFFERENT VIEWS OF OPERATING SYSTEM
- User's View
- System View
USER VIEW:
- From the user’s point of view, the computer is the interface being used.
- Such systems are designed for one user to monopolize its resources, to maximize the work that the user is performing.
- In these cases, the operating system is designed mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.
SYSTEM VIEW:
- From the System's point of view, the operating system is the program that is most intimate with the hardware.
- The Operating system is viewed as a resource allocator. A computer system has many resources- hardware and software-that may be required to solve a problem: CPU time, memory space, file-storage space, I/O devices, and so on.
- The operating system acts as the manager of these resources.
- An operating system is a control program. A control program manages the execution of user programs to prevent errors and improper use of the computer. The fundamental goal of computer systems is to execute user programs and to make solving user problems easier.
SYSTEM GOALS
- The primary goal of some operating system is convenience for the user. Operating systems exist because they are supposed to make it easier to compute with them than without them.
- The primary goal of other operating systems is efficient operation of the Computer system.In this case for large, shared, multiuser systems. These Systems are expensive, so it is desirable to make them as efficient as possible.
FUNCTIONS AND MANAGEMENT TASK OF OPERATING SYSTEM
- Processor management
- Memory management
- Device management
- File Management
- Security: Preventing unauthorized access to programs and data.
- Error detecting
- Application that allows standard communication between software and your computer.
- User interface: This allows you to communicate with your computer.
Processor management
- Operating system decides which task (process) gets the processor (CPU) when and how much time it will take.
- Allocation and De-allocation of processor (CPU) to processes when required.
- Keeps tracks of processor and status of process by program called traffic controller
- Operating system decides which task (process) gets the processor (CPU) when and how much time it will take.
- Allocation and De-allocation of processor (CPU) to processes when required.
- Keeps tracks of processor and status of process by program called traffic controller
Memory management
- Operating System manages Main Memory. Main memory provides a fast storage that can be access directly by the CPU. A programs to be executed, must in the main memory.
- Keeps track of Main memory: Which part is used and not in used is tracked by Operating System.
- Allocation and De-allocation of memory : Allocation of memory to process when process requests it and De-allocation of memory when the process no needs it.
- OS (operating system) decides which process will get memory when and how much.
- Operating System manages Main Memory. Main memory provides a fast storage that can be access directly by the CPU. A programs to be executed, must in the main memory.
- Keeps track of Main memory: Which part is used and not in used is tracked by Operating System.
- Allocation and De-allocation of memory : Allocation of memory to process when process requests it and De-allocation of memory when the process no needs it.
- OS (operating system) decides which process will get memory when and how much.
Device management
- OS manages device communication via their respective drivers.
- OS decides which process gets device, when and how much time.
- Using I/O controller OS keeps tracks of all devices. Allocation and De-allocation of Devices.
- OS manages device communication via their respective drivers.
- OS decides which process gets device, when and how much time.
- Using I/O controller OS keeps tracks of all devices. Allocation and De-allocation of Devices.
File Management
- Keep track of who gets the resources.
- Operating System keeps track of Status, location and uses of Resources.
- Allocation of resources when requested and De-allocation of resources.
- Keep track of who gets the resources.
- Operating System keeps track of Status, location and uses of Resources.
- Allocation of resources when requested and De-allocation of resources.
Security: Preventing unauthorized access to programs and data.
Error detecting
Application which allows standard communication between software and your computer.
User interface: The OS provide a graphical user interface for higher functions. This allows you to communicate with your computer.
TYPES OF OPERATING SYSTEM
- Batched operating system
- Multi-programmed operating system
- Timesharing operating system
- Network operating system
- Distributed operating system
- Real-time operating system
- Multi-processor operating system
BATCH OPERATING SYSTEM
“The operating system is termed as “batch operating” because the input data (job) are collected into batches or sets of records with similar needs and each batch is processed as a unit(group). The output is another batch that can be reused for computation.”
- In this OS the user did not interact directly with the computer systems.
- The user prepared a job(input data) using off-line device like punch cards,and submitted it to the computer operator.
- After some time the output appeared. The output consisted of the result of the program, as well as a dump of the final memory and register contents for debugging.
- To speed up processing, operators batched together jobs with similar needs and ran them through the computer as a group. Thus, the programmers would leave their programs with the operator.
- The output from each job would be sent back to the appropriate programmer. In this execution environment, the CPU is often idle, because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic devices.
- Operating System's major task was to transfer control automatically from one job to the next. The operating system was always resident in memory.
- In batch environment process is created in response to the submission of a job.
- The user prepared a job(input data) using off-line device like punch cards,and submitted it to the computer operator.
- After some time the output appeared. The output consisted of the result of the program, as well as a dump of the final memory and register contents for debugging.
- To speed up processing, operators batched together jobs with similar needs and ran them through the computer as a group. Thus, the programmers would leave their programs with the operator.
- The output from each job would be sent back to the appropriate programmer. In this execution environment, the CPU is often idle, because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic devices.
- Operating System's major task was to transfer control automatically from one job to the next. The operating system was always resident in memory.
- In batch environment process is created in response to the submission of a job.
ADVANTAGES:
- Batch processing takes much of the work of the operator to the computer.
- Increased performance as a new job gets started as soon as the previous job finished without any manual intervention.
- Increased performance as a new job gets started as soon as the previous job finished without any manual intervention.
DISADVANTAGES:
- Difficult to debug program.
- A job could enter an infinite loop.
- Due to the lack of protection scheme, one batch job can affect pending jobs.
- A job could enter an infinite loop.
- Due to the lack of protection scheme, one batch job can affect pending jobs.
EXAMPLE :
- IBM’s OS360 is a popular batch processing system
MULTIPROGRAMMED OPERATING SYSTEM
“The multiprogramming is interleaved execution of multiple jobs by the same computer.Multiprogramming does mean that there are a number of jobs available to the CPU.To overcome the problem of utilization of CPU and main memory, the multiprogramming was introduced.”
- A program in execution is called a "Process", "Job" or a "Task".
- In multiprogramming system,The operating system keeps several jobs in memory Simultaneously.When one program(task/job) is waiting for I/O transfer; there is another program ready to utilize the CPU.
- So it is possible for several jobs to share the time of the CPU.
- In multiprogramming the execution of jobs is not defined at the same instance of time. Multiprogramming does mean that there are a number of jobs available to the CPU.
- In multiprogramming system,The operating system keeps several jobs in memory Simultaneously.When one program(task/job) is waiting for I/O transfer; there is another program ready to utilize the CPU.
- So it is possible for several jobs to share the time of the CPU.
- In multiprogramming the execution of jobs is not defined at the same instance of time. Multiprogramming does mean that there are a number of jobs available to the CPU.
- A simple process of multiprogramming is shown in given figure. As given in fig. at the particular situation, job' A' is not utilizing the CPU time because it is busy in I/ 0 operations.
- Hence the CPU becomes busy to execute the job 'B'.
- Another jobs C, D, E, F are waiting for the CPU time for getting its execution time. So in this state the CPU will never be idle and utilizes maximum of its time.
- Multiprogramming is a common approach to resource management.
- The difference between non-multiprogrammed system and multiprogrammed system is that in the non-multiprogrammed system, the CPU would sit idle while, in a multiprogramming system, the operating system simply switches to another job, and executes it.
- This idea is common in other life situations. A lawyer does not work for only one client at a time. While one case is waiting to go to trial or have papers typed, the lawyer can work on another case.
- If she/he has enough clients,the lawyer will never be idle for lack of work.
- Hence the CPU becomes busy to execute the job 'B'.
- Another jobs C, D, E, F are waiting for the CPU time for getting its execution time. So in this state the CPU will never be idle and utilizes maximum of its time.
- Multiprogramming is a common approach to resource management.
- The difference between non-multiprogrammed system and multiprogrammed system is that in the non-multiprogrammed system, the CPU would sit idle while, in a multiprogramming system, the operating system simply switches to another job, and executes it.
- This idea is common in other life situations. A lawyer does not work for only one client at a time. While one case is waiting to go to trial or have papers typed, the lawyer can work on another case.
- If she/he has enough clients,the lawyer will never be idle for lack of work.
TIME-SHARING/MULTITASKING OPERATING SYSTEM
“CPU's (Processor's) time which is shared among multiple users simultaneously is called as time-sharing.Time sharing or multitasking is a logical extension of multiprogramming.In Time-sharingmany users located at various places(terminal), can use a particular computer system at the same time.The CPU executes multiple jobs by switching among them, the switches occur so frequently that the users can interact with each program while it is running.”
- A time-shared operating system allows many users to share the computer simultaneously.
- Difference between Multiprogrammed Batch Systems and Time-Sharing Systems:
o In multiprogrammed batch systems, objective is to maximize processor use, On the other hand Time-Shared Systems objective is to minimize response time.
o In multiprogrammed system CPU spends fixed amount of time on one program before moving to another.
o Where as In time sharing environment, thousands of users are each allocated a tiny slice of computer time(about 2 millisecond).In this time slot,each user is free to perform any required operation.At the end of time period,another user is given time slice of the CPU.This arrangement permits many users to be connected to a CPU simultaneously.
- An interactive (or hands-on) computer system provides direct communication between the user and the system. The user gives instructions to the operating system or to a program directly, using a keyboard or a mouse, and waits for immediate results.
- A time-shared operating system allows many users to share the computer simultaneously.Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user. As the system switches rapidly from one user to the next, each user is given the impression that the entire computer system is dedicated to her/his use, even though it is being sharedamong many users.
- A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer.Each user has at least one separate program in memory.
- Difference between Multiprogrammed Batch Systems and Time-Sharing Systems:
o In multiprogrammed batch systems, objective is to maximize processor use, On the other hand Time-Shared Systems objective is to minimize response time.
o In multiprogrammed system CPU spends fixed amount of time on one program before moving to another.
o Where as In time sharing environment, thousands of users are each allocated a tiny slice of computer time(about 2 millisecond).In this time slot,each user is free to perform any required operation.At the end of time period,another user is given time slice of the CPU.This arrangement permits many users to be connected to a CPU simultaneously.
- An interactive (or hands-on) computer system provides direct communication between the user and the system. The user gives instructions to the operating system or to a program directly, using a keyboard or a mouse, and waits for immediate results.
- A time-shared operating system allows many users to share the computer simultaneously.Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user. As the system switches rapidly from one user to the next, each user is given the impression that the entire computer system is dedicated to her/his use, even though it is being sharedamong many users.
- A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer.Each user has at least one separate program in memory.
ADVANTAGES OF TIMESHARING OPERATING SYSTEMS:
- Provide advantage of quick response.
- Avoids duplication of software.
- Reduces CPU idle time.
- Avoids duplication of software.
- Reduces CPU idle time.
DISADVANTAGES OF TIMESHARING OPERATING SYSTEMS:
- Reliability issue.
- Question of security and integrity of user programs and data.
- Problem of data communication.
- Question of security and integrity of user programs and data.
- Problem of data communication.
NETWORK OPERATING SYSTEM
“A network operating system, or NOS, is system software that is designed primarily to controls the various devices like printers, disk drives on a computer network and how they communicate with each other.”
- Network operating system is client – server Architecture model.
- Some tasks of a Network Operating System are similar to those of an OS for individual computers, such as memory management and hardware control.
- A network, in the simplest terms, is a communication path between two or more systems.
- However, a network OS also has specialized tasks. For example, when network devices are used, such as printers and disk drives, the Network operating system ensures these resources are used correctly and efficiently.Specialized functions also include network security and network administration.
Benefits/advantages of Network Operating System:
• Sharing: NOS provide printer sharing, common file system sharing and database sharing, application sharing,
• Management: Network Operating System (NOS) has the ability to manage a network name directory, network security,and network administration. Network security is server managed.
• Remote access: Access to resources of various machines is done explicitly by remote logging into the appropriate remote machine or transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism.
• Ease of Up-gradation: Upgrades to new technologies and hardware can be easily integrated into the system.
- Some tasks of a Network Operating System are similar to those of an OS for individual computers, such as memory management and hardware control.
- A network, in the simplest terms, is a communication path between two or more systems.
- However, a network OS also has specialized tasks. For example, when network devices are used, such as printers and disk drives, the Network operating system ensures these resources are used correctly and efficiently.Specialized functions also include network security and network administration.
Benefits/advantages of Network Operating System:
• Sharing: NOS provide printer sharing, common file system sharing and database sharing, application sharing,
• Management: Network Operating System (NOS) has the ability to manage a network name directory, network security,and network administration. Network security is server managed.
• Remote access: Access to resources of various machines is done explicitly by remote logging into the appropriate remote machine or transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism.
• Ease of Up-gradation: Upgrades to new technologies and hardware can be easily integrated into the system.
- Some disadvantages of network operating systems are: High cost of running server,central location dependency for most of all operation and regular updates and maintenance are required.
EXAMPLE OF NETWORK OPERATING SYSTEM:
• Artisoft's LANtastic
• Banyan VINES
• Novell's NetWare
• Microsoft's LAN Manager
• Windows NT and Digital's OpenVMS come with capabilities that enable them to be described as a network operating system.
• Banyan VINES
• Novell's NetWare
• Microsoft's LAN Manager
• Windows NT and Digital's OpenVMS come with capabilities that enable them to be described as a network operating system.
DISTRIBUTED OPERATING SYSTEM
“Distributed Operating System is a system where distributed applications are running on multiple computers linked by communication lines, such as high speed buses or telephone lines.Distributed systems use multiple central processors to serve multiple real time application andmultiple users.”
- A distributed operating system is an extension of the network operating system that supports higher levels of communication and integration of the machines on the network.
- A network, in the simplest terms, is a communication path between two ormore systems. Distributed systems depend on networking for their functionality.
- By being able to communicate, distributed systems are able to share computational tasks, and provide a rich set of features to users.
- Networks vary by the protocols used, the distances between nodes, andthe transport media. TCP/IP is the most common network protocol.
- To an operating system, a network protocolsimply needs an interface device-a network adapter.
- This system looks to its users like an ordinary centralized operating system but runs on multiple, independent central processing units (CPUs).
- These systems are referred as loosely coupled systems where each processor has its own local memory and processors communicate with one another through various communication lines, such as high speed buses or telephone lines. Loosely coupled systems, mean that such computers possess no hardware connections at the CPU - memory bus level, but are connected by external interfaces that run under the control of software.
- By being able to communicate, distributed systems are able to share computational tasks, and provide a rich set of features to users.
- Networks vary by the protocols used, the distances between nodes, andthe transport media. TCP/IP is the most common network protocol.
- To an operating system, a network protocolsimply needs an interface device-a network adapter.
- This system looks to its users like an ordinary centralized operating system but runs on multiple, independent central processing units (CPUs).
- These systems are referred as loosely coupled systems where each processor has its own local memory and processors communicate with one another through various communication lines, such as high speed buses or telephone lines. Loosely coupled systems, mean that such computers possess no hardware connections at the CPU - memory bus level, but are connected by external interfaces that run under the control of software.
DISTRIBUTED SYSTEMS PROVIDE THE FOLLOWING ADVANTAGES:
1 Sharing of resources: Access to remote resources similar to access to local resources means With resource sharing facility user at one site may be able to use the resources Available at another
2 Reliability:Distributed systems are potentially more reliable than a central system because if a system has only one instance of some critical component, such as a CPU, disk, or network interface, and that component fails, the system will go down. If one site fails in a distributed system, the remaining sites can potentially continue Operating.
3 Communication:These systems are loosely coupled systems where each processor communicates with one another through various communication lines, such as high speed buses or telephone lines.
4 Computation speedup: transfer the computation, rather than the data, across the system.
2 Reliability:Distributed systems are potentially more reliable than a central system because if a system has only one instance of some critical component, such as a CPU, disk, or network interface, and that component fails, the system will go down. If one site fails in a distributed system, the remaining sites can potentially continue Operating.
3 Communication:These systems are loosely coupled systems where each processor communicates with one another through various communication lines, such as high speed buses or telephone lines.
4 Computation speedup: transfer the computation, rather than the data, across the system.
THE EXAMPLES OF DISTRIBUTED OPERATING SYSTEMS:
• IRIX operating system; is the implementation of UNIX System V, Release 3 for Silicon Graphics multiprocessor workstations.
• DYNIX operating system running on Sequent Symmetry multiprocessor computers.
• AIX operating system for IBM RS/6000 computers.
• Solaris operating system for SUN multiprocessor workstations.
• Mach/OS is a multithreading and multitasking UNIX compatible operating system;
• OSF/1 operating system developed by Open Foundation Software: UNIX compatible.
• LOCUS and MICROS are the best examples of distributed operating systems.
- Using LOCUS operating system it was possible to access local and distant files in uniform manner. This feature enabled a user to log on any node of the network and to utilize the resources in a network without the reference of his/her location.
- MICROS provided sharing of resources in an automatic manner. The jobs were assigned to different nodes of the whole system to balance the load on different nodes.
• DYNIX operating system running on Sequent Symmetry multiprocessor computers.
• AIX operating system for IBM RS/6000 computers.
• Solaris operating system for SUN multiprocessor workstations.
• Mach/OS is a multithreading and multitasking UNIX compatible operating system;
• OSF/1 operating system developed by Open Foundation Software: UNIX compatible.
• LOCUS and MICROS are the best examples of distributed operating systems.
- Using LOCUS operating system it was possible to access local and distant files in uniform manner. This feature enabled a user to log on any node of the network and to utilize the resources in a network without the reference of his/her location.
- MICROS provided sharing of resources in an automatic manner. The jobs were assigned to different nodes of the whole system to balance the load on different nodes.
REAL TIME OPERATING SYSTEM (RTOS)
“Real time system is defines as a data processing system in which each task has a deadline to complete. Real Time Operating System (RTOS) adheres to this deadline as missing a deadline can cause affects ranging from undesired to catastrophic. A real-time system has well-defined, fixed time constraints.”
- Let’s understand Real Time Operating System with real life example:
- Suppose a person is driving a car on a highway at a speed of 80 km per hour. Now, unfortunately the car meets with an accident. Fortunately, the airbag deployed at the right time and saved the life of the driver.
- So, we see that airbag is a very good feature in a car which can save a life someday. But, what would have happened if the airbag would have deployed a few seconds late? Yes, we would have lost a life.
- So just imagine the dependency on the accuracy of opening of the airbag.
- The time taken by the system to respond to an input and display of required updated information is termed as response time. So in this method response time is very less as compared to the online processing.
- Real time processing is always on line whereas on line system need not be real time.
o Online processing: Processing performed under the direct control of the CPU whilst the remains in communication user with the computer.
o Offline processing: Processing which is done away from CPU.
- Real-time operating system has well-defined, fixed time constraints other wise system will fail. For example Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, and home-appliance controllers, Air traffic control system etc.
- Suppose a person is driving a car on a highway at a speed of 80 km per hour. Now, unfortunately the car meets with an accident. Fortunately, the airbag deployed at the right time and saved the life of the driver.
- So, we see that airbag is a very good feature in a car which can save a life someday. But, what would have happened if the airbag would have deployed a few seconds late? Yes, we would have lost a life.
- So just imagine the dependency on the accuracy of opening of the airbag.
- The time taken by the system to respond to an input and display of required updated information is termed as response time. So in this method response time is very less as compared to the online processing.
- Real time processing is always on line whereas on line system need not be real time.
o Online processing: Processing performed under the direct control of the CPU whilst the remains in communication user with the computer.
o Offline processing: Processing which is done away from CPU.
- Real-time operating system has well-defined, fixed time constraints other wise system will fail. For example Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, and home-appliance controllers, Air traffic control system etc.
RTOS CAN BE CLASSIFIED INTO THREE TYPES:
• Hard RTOS: These types of RTOS strictly adhere to the deadline associated with the tasks. Missing on a deadline can have catastrophic affects. The air-bag example we discussed in the beginning of this article is example of a hard RTOS as missing a deadline there could cause a life.
• Firm RTOS: These types of RTOS are also required to adhere to the deadlines because missing a deadline may not cause a catastrophic affect but could cause undesired affects, like a huge reduction in quality of a product which is highly undesired.
• Soft RTOS: In these type of RTOS, missing a deadline is acceptable. For example On-line Databases. Features of an RTOS:
- Context switching latency should be short: This means that the time taken while saving the context of current task and then switching over to another task should be short.
- The time taken between executing the last instruction of an interrupted task and executing the first instruction of interrupt handler should be predictable and short. This is also known as interrupt latency.
- Similarly the time taken between executing the last instruction of the interrupt handler and executing the next task should also be short and predictable. This is also known as interrupting dispatch latency.
- Reliable and time bound inter process mechanisms should be in place for processes to communicate with each other in a timely manner.
- An RTOS should have support for multitasking and task preemption. Preemption means to switch from a currently executing task to a high priority task ready and waiting to be executed.
• Firm RTOS: These types of RTOS are also required to adhere to the deadlines because missing a deadline may not cause a catastrophic affect but could cause undesired affects, like a huge reduction in quality of a product which is highly undesired.
• Soft RTOS: In these type of RTOS, missing a deadline is acceptable. For example On-line Databases. Features of an RTOS:
- Context switching latency should be short: This means that the time taken while saving the context of current task and then switching over to another task should be short.
- The time taken between executing the last instruction of an interrupted task and executing the first instruction of interrupt handler should be predictable and short. This is also known as interrupt latency.
- Similarly the time taken between executing the last instruction of the interrupt handler and executing the next task should also be short and predictable. This is also known as interrupting dispatch latency.
- Reliable and time bound inter process mechanisms should be in place for processes to communicate with each other in a timely manner.
- An RTOS should have support for multitasking and task preemption. Preemption means to switch from a currently executing task to a high priority task ready and waiting to be executed.
Some of the most widely used RTOS are:
LynxOS
OSE
QNX
RTLinux
VxWorks
Windows CE
LynxOS
OSE
QNX
RTLinux
VxWorks
Windows CE
MULTIPROCESSOR OPERATING SYSTEM
“Multiprocessor systems also known as parallel systems or tightly coupled systems have more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral devices.”
TYPES OF MULTIPROCESSOR SYSTEM:
• Shared memory multiprocessor system: a natural extension of a single processor system in which all the processors can access a common memory.
• Distributed memory multicomputer system : multiple interconnected computers where each computer has its own memory.
• Distributed memory multicomputer system : multiple interconnected computers where each computer has its own memory.
MULTIPROCESSOR SYSTEMS HAVE THREE MAIN ADVANTAGES:
1. Increased throughput. When multiple processors cooperate on a task, a certain amount of overhead is incurred in keeping all the parts working correctly.
2. Economy of scale. Multiprocessor systems can save more money than multiple single-processor systems, because they can share peripherals, mass storage, and power supplies.
3. Increased reliability. If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down.
• The multiple-processor systems use symmetric multiprocessing (SMP), in which each processor runs an identical copy of the operating system, and these copies communicate with one another as needed.
• SMP means that all processors are peers; no master-slave relationship exists between processors. Each processor concurrently runs a copy of the operating system.
• An example of the SMP system is Encore's version of UNIX for the Multi max computer.
• Some systems use asymmetric multiprocessing, in which each processor is Assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.
2. Economy of scale. Multiprocessor systems can save more money than multiple single-processor systems, because they can share peripherals, mass storage, and power supplies.
3. Increased reliability. If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down.
• The multiple-processor systems use symmetric multiprocessing (SMP), in which each processor runs an identical copy of the operating system, and these copies communicate with one another as needed.
• SMP means that all processors are peers; no master-slave relationship exists between processors. Each processor concurrently runs a copy of the operating system.
• An example of the SMP system is Encore's version of UNIX for the Multi max computer.
• Some systems use asymmetric multiprocessing, in which each processor is Assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.
DIFFERENCE BETWEEN NETWORK OPERATING SYSTEM AND DISTRIBUTED OPERATING SYSTEM:
Network Operating System (NOS)
|
Distributed Operating System (DOS)
|
| Users are aware of multiplicity of machines. | Users are not aware of multiplicity of machines. |
| Access to resources of various machines is done explicitly by remote logging into the appropriate remote machine or transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism. | Access to remote resources similar to access to local resources. |
| Transfer the data, to and from the remote server and only the server performs the all or most of the computation. | Transfer the computation, rather than the data, across the system. |
| Execute an entire process, or parts of it, at the remote server. | Execute an entire process, or parts of it, at different sites. |
| Run process remotely, and needs to transfer all the data to the server for processing. | Run process remotely, rather than transfer all data locally. |
| Employs a client-server model | Employs a master-sl |
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