Processor pool model in distributed computing system

Before we start, the prerequisites are to have knowledge about the distributed system.

What is distributed system?

A distributed system is a collection of an independent computer that appears to its user as a coherent (logical) system.

A distributed system consists of concurrent (parallel) processors accessing distributed resources. It consists of autonomous computers linked by a computer network and equipped with a distributed system software. Resources are shared through message passing in a network environment that may be unreliable and contain untrusted components.

Layout of distributed system

What is processor pool?

An approach to the construct of processor pool, a full of Central Processing Units (CPUs) within the machine room, which can be allocated dynamically to users on demand.

Instead of giving individual workstations to users, the processor pool model given high-performance graphics terminals. Actually, this approach is based on the observation on What users really want is a good performance and high-quality graphical interface. It is built with low-cost microprocessors also, the concept known as traditional time-sharing is much closer than the Personal Computers (PCs) model.

A system based on processor pool model of distributed system

Processor-pool Model

• The processor pool model consists of multiple processors and group of workstations.
• The model is based on the observation that most of the time a user does not need any computing power.
• In this model, the process is pooled together to be shared by the users as needed.
• The processor pool of process consists of large microcomputers and minicomputers attached to the network.
• Each processor has its own memory to load and run.
• The processors in the pool have no terminals attached directly to them, and the user accesses the system from terminals that are attached to the network via a special device.

Motivation of processor pool model

A diskless workstation is a step further which is the actual motivation of processor pool model.

A diskless workstation or you can say that a diskless node is a personal computer or workstation working without disk drives, which uses client network booting to load its basic operating system from a server. A personal computer may be known as diskless node also if the disk attached within it is damaged or not working and use network booting option to load OS.

Diskless workstation

Queuing theory

To centralising the power of computing into a processor pool actually comes from Queuing theory is the huge argument. A situation is known as queuing systems. If the server can handle 100 requests/sec, but the users continuously generate 110 requests/sec, the queue will grow without bound. Client continuously sending 110 requests/sec and the server capacity is 100 requests/sec to handle, at that time queue will grow without bound.

A basic queuing system based on Queuing theory

Formal Models of distributed systems

Models of distributed computing

There are other two types of computing models:

• Workstation model
• Workstation-server model

1. It is economically more viable to use a few high-end costly servers and more diskless workstations. Diskless workstations are easier to maintain than disk full ones.
2. In a workstation-server model, the request-response protocol indicates that the client does not get burdened and the process migration becomes unnecessary.
3. The user also has the flexibility of changing his workstation.
4. A workstation is connected in a suitable network configuration using the star topology.
5. Workstation-server model consists of multiple workstations coupled with powerful servers with extra hardware to store the file systems and other software.
6. Workstation-server model is suitable for sharing the resources between different systems in a modular fashion.
7. The processor-pool model uses computing resources more effectively, all the resources of the system being available to present working users.
8. Workstation-server model offers services only to individual clients.
9. A hybrid model of a distributed system may be built by combining the features of the workstation-server model and the processor pool model.