Real Time or Reactive Systems are systems subject to time constraints. These are bounds which act as operational deadlines for processes.
While driving a vehicle, if we apply the breaks for a particular time(bound), the car stops. Similarly, if a bound is met the process stops.
A system may be classified as soft real time(deadlines met generally) or hard real time(deadlines met deterministically).
A soft real time may only lead to decrease in service quality while a heard real time may lead to complete failure of the system on meeting a bound.
Real time systems are used to guarantee that deadlines are met, are where throughput is not the major aim. These are used largely in medical equipment, missile systems, etc.
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Distributed Computing Systems consist of multiple computers which together form & communicate through a computer network.
A program is divided(distributed) into many individual jobs, each of which is then solved by the computers in the network. One job, per computer.
This is in contrast to parallel systems, where the job is divided but solved by the same computer.
Hence, in case of parallel systems, we have the same memory but different processes, while in case of distributed systems, there are different processes on different memory units.
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(A4) Parallel Computing Systems:
In parallel systems, large jobs are divided into smaller ones which are then processed simultaneously(hence, the name parallel). Since, the task is broken down, the efficiency largely increases.
Parallel computing has a number of advantages over other paradigms:
-It leads to a large increase in efficiency.
-It helps in power consumption.
It is the hence, the most dominant paradigm in computer architecture.
The disadvantages regarding parallel computing are:
-The processes difficult to write.
-Gives more scope for bugs to crawl in.
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(A3) Time Sharing Systems
The main idea of time sharing systems is to allow a large number of users to interact with a single computer(system) concurrently.
Hence, it extended the idea of multiprogramming to allow multiple terminals with each-in-use terminal to be associated with one or more jobs.
Hence, the there are spaces for more than one user, each associated with a program or more.
The main objective of these systems is to minimize the response time to user commands.
(and lead to interactive work)
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In Multiprogramming Batch systems, when one job waits for the completion of an I/O operation, another is executed.
A multiprogramming system is responsible for:
-starting jobs
-taking I/P for jobs
-switching between jobs
(& ensuring protection while doing so)
Classified jobs as foreground and background jobs.
When a foreground jobs encounters an operation requiring input or giving output to the user, a background job is executed.
Hence, more than one program could be executed, but, by the same user.
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