ENVS 1500 Lecture 21: ENVS 1500 Lecture 21 Notes

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ENVS 1500 Lecture 21 Notes Conversational System
Introduction
As a student, you are probably most familiar with interactive systems.
When the system is interactive, the user interacts directly with the program to provide
input data and guidance during program execution.
Interactive systems are sometimes known as conversational systems.
Most personal computing is done interactively.
Many business tasks are performed more effectively in a batch, where the data input for
the program is collected together into a file on disk or tape.
It does not make sense to have a user enter data one record at a time if an entire set of
data is to be processed into monthly credit card bills, for example.
Instead, the user submits the program(s), or job(s), to the computer for processing.
This type of processing is known as batch processing.
The user does not interact with the program during batch processing.
Large-scale billing, payroll, and other similarly data intensive systems are usually
processed this way.
We remind you that a CPU can execute only one instruction at a time
Therefore, time used by the operating system on a single CPU system is not available for
the execution of user programs.
In general, the time used by the OS program is considered overhead.
In reality, though, the operating system actually saves time for the users in most
situations
In a single-user system, the operating system program creates minimal overhead.
While the OS program is available to the user at any time, the executing user programs
have priority
The OS program runs only to distribute CPU time among executing programs
To hadle iterrupts, or if the users’ programs request its services
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