A real-time system is used when there are rigid time requirements on the operation of a processor or the flow of data, and thus is often used as a control device in a dedicated application. Sensors bring data to the computer. The computer must analyze the data and possibly adjust controls to modify the sensor inputs. Systems that control scientific experiments, medical imaging systems, industrial control systems, and some display systems are real-time systems. Also included are some automobile-engine fuel-injection systems, home-appliance controllers, and weapon systems.

1. Operating System 10
Real Time Operating System
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Real Time Systems
• Another form of a special-purpose operating system is
the real-time system.
• A real-time system is used when there are rigid time
requirements on the operation of a processor or the
flow of data, and thus is often used as a control device
in a dedicated application.
• Sensors bring data to the computer. The computer must
analyze the data and possibly adjust controls to modify
the sensor inputs.
• Systems that control scientific experiments, medical
imaging systems, industrial control systems, and some
display systems are real-time systems.
• Also included are some automobile-engine fuel-injection
systems, home-appliance controllers, and weapon
systems.

3. Real Time Systems
• A real-time system is defined as a data processing system in
which the time interval required to process and respond to
inputs is so small that it controls the environment.
• The time taken by the system to respond to an input and
display of required updated information is termed as the
response time.
• Real-time systems are used when there are rigid time
requirements on the operation of a processor or the flow of
data and real-time systems can be used as a control device in
a dedicated application.
• A real-time operating system must have well-defined, fixed
time constraints, otherwise the system will fail.

4. Real Time Systems : Time
Constraint
• A real-time operating system has well-defined, fixed time
constraints.
• Processing must be done within the defined constraints,
or the system will fail.
• For instance, it would not do for a robot arm to be
instructed to halt after it had smashed into the car it
was building.
• A real-time system is considered to function correctly
only if it returns the correct result within any time
constraints.
• Contrast this requirement to a time-sharing system,
where it is desirable (but not mandatory) to respond
quickly, or to a batch system, where there may be no
time constraints at all.

5. Hard Real Time Systems
• A hard real-time system guarantees that critical
tasks complete on time.
• This goal requires that all delays in the system
be bounded, from the retrieval of stored data to
the time that it takes the operating system to
finish any request made of it.
• Such time constraints dictate the facilities that
are available in hard real-time systems
• Secondary storage of any sort is usually limited
or missing, with data instead being stored in
short-term memory, or in read-only memory
(ROM).

6. Hard Real Time Systems
• Most advanced operating-system features are absent
too, since they tend to separate the user further from
the hardware, and that separation results in
uncertainty about the amount of time an operation
will take.
• For instance, virtual memory is almost never found
on real-time systems.
• Therefore, hard real-time systems conflict with the
operation of time-sharing systems, and the two
cannot be mixed.
• Since none of the existing general-purpose operating
systems support hard real-time functionality

7. Soft Real Time Systems
• A less restrictive type of real-time
system is a soft real-time system,
where a critical real-time task gets
priority over other tasks, and retains
that priority until it completes.

8. Memory Management in RTS
• Memory Management: In real-time operating
system there is a little swapping of program
between primary and secondary memory.
• Most of die time, processes remain in primary
memory in order to provide quick response,
therefore, memory management in real-time
system is less demanding compared to other
types of multiprogramming system.
• On the other hand, processes in real- time system
tend to cooperate closely thus providing feature
for both protection and sharing of memory

9. I/O Management in RTS
• I/O Management: Time-critical device
management is one of the main
characteristics of real-time systems.
• It also provides sophisticated form of
interrupt management and I/O buffering.

10. File Management in RTS
• File Management: The primary objective of file
management in real-time systems is usually the
speed of access rather than efficient utilisation of
secondary storage.
• In fact, some embedded real-time systems does
not have secondary memory.
• However, where provided file management of
real-time system must satisfy the same
requirement as those found in time sharing and
other multiprogramming systems

11. Assignment
• Explain the concept of real time operating
system