Transcript Batch Processing and Timesharing

Industrial Computer
Systems
6032B
Mount Druitt College of TAFE
Lesson 3
© Mike Stacey 2008
1
Today’s Topics



Batch processing
Timesharing
Batch files
© Mike Stacey 2008
2
Batch Processing and
Timesharing
Industrial Computer Systems
Mt Druitt College of TAFE
Semester 1, 2008
© Mike Stacey 2008
3
Early Operating Systems

Program execution required preparation of
equipment




mounting tapes
placing punched cards in the card reader
setting switches and so on
If multiple users wanted to share a machine,
sign on sheets were provided so that users
could reserve a machine for a period of time
(session)
© Mike Stacey 2008
4
Batch Processing





Development of computers was involved with streamlining the
transition between jobs and simplifying program set-up
Computer operator hired to perform the operation of the
machine. Users were not permitted into the computer room.
Users submitted their program along with written instructions to
the computer operator and returned later for the results
Operator loaded the programs into the machine’s mass storage
where the operating system could access them for execution
This was the beginning of BATCH PROCESSING
 the execution of jobs by collecting them in a single batch, then
executing them without further intervention from the user
 the jobs residing in mass storage awaited execution in a job
queue
© Mike Stacey 2008
5
Disadvantage of Batch
processing

No user interaction with program while being run





OK for jobs such as payroll processing
Not OK for jobs such as airline reservations – cancellations
and reservations must be entered as they occur
New operating systems were developed to
accommodate these needs
Execution of programs carried on a dialogue with
the user (interactive processing)
Still a problem that only one program can execute at
any one time
© Mike Stacey 2008
6
Multitasking - Timesharing





So the next development was to allow multiple
programs to simultaneously run on the machine
The operating system rotates jobs (programs) in and
out of execution
Each process is allocated a time slice and can only
execute during that interval of time
Called Timesharing
If this process is performed with great speed, the
illusion of several jobs running at the same time is
created
© Mike Stacey 2008
7
Example of Timesharing

These days, everyone sees examples of
timesharing when they are running more than
one program at once on a PC


MS Word, MS Excel, Internet Explorer, Windows
Explorer are all separate processes (programs,
jobs) and they appear to be running
simultaneously
In reality they are running as follows:
© Mike Stacey 2008
8
Scheduling algorithms


Various different algorithms control which
process is running at a particular time
One of the more common scheduling
algorithms is called Round Robin scheduling
© Mike Stacey 2008
9
Round Robin Scheduling
P2
P3
P1
2 time
units
CPU
executing
2 time
units
P4
2 time
units
2 time
units
2 time
units
P8
2 time
units
2 time
units
P7
Some examples of
P1, P2, P3 etc
would be?
P5
2 time
units
P6
Run process for one time slice then move
it to back of job queue, load next process
into memory, execute it...
© Mike Stacey 2008
10