PROCESSES AND OPERATING SYSTEMS
1. Define Process.
can be defined as a program unit in execution the state of which is controlled
by OS. It is a single execution of a program. Process is also defined as
computational unit, which is scheduled and runs on the CPU by a kernel. Kernel
controls the creation of the process and states of the process.
2. Define Thread.
a light weight process. Processes that share the same address space are often
3. What are multi rate systems?
embedded computing systems are very common, including automobile engines,
printers, and cell phones. In all these systems, certain operations must be
executed periodically, and each operation is executed at its own rate.
4. What is release time and deadline of a process?
release time is the time at which the process becomes ready to execute. A
deadline specifies when a computation must be finished. The deadline for an
aperiodic process is generally measured from the release time, since that is
the only reasonable time reference.
5. What is the period and rate of a process?
period of a process is the time between successive executions. The process’s
rate is the inverse of its period.
6. What is a task graph?
A set of
processes with data dependencies is called a task graph.
7. Define CPU utilization.
is the ratio of the CPU time that is being used for useful computations to the
available CPU time. This ratio ranges between 0 and 1, with 1 meaning that all
CPU time is being used for system purposes.
8. What are the three basic scheduling states of a
9. Define scheduling policy.
scheduling policy defines how processes are selected for promotion from the
ready state to the running state.
10. What is hyperperiod?
is the least-common multiple of the periods of all the processes. It is a
finite period that covers all possible combinations of process executions.
11. What is scheduling overhead?
execution time required to choose the next execution process, which is incurred
in addition to any context switching overhead is the scheduling overhead.
12. What do you mean by a context switch?
of registers that define a process are known as its context and switching from
one process’s register set to another is known as context switching.
13. What is process control block?
structure that holds the state of the process is known as the process control
14. What are two major ways to assign priorities to
two major ways to assign priorities: static priorities that do not change
during execution and dynamic priorities that do change.
15. What is Rate monotonic analysis (RMS)?
monotonic analysis is the theory behind the Rate monotonic scheduling. The
simple model of the system is as follows,
run periodically on a single CPU. Context switching time is ignored.
no data dependencies between processes. The execution time for a process is
deadlines are at the ends of their periods.
highest-priority ready process is always selected for execution.
the response time and critical instant of a process?
response time of a process is the time at which the process finishes.
critical instant for a process is defined as the instant during execution at
which the task has the largest response time.
17. What are the two ways of process communication?
can send a communication in one of two ways: blocking or Non-blocking. After
sending a blocking communication, the process goes into the waiting state until
it receives a response. Non-blocking communication allows the process to
continue execution after sending the communication.
18. Define earliest deadline first scheduling
deadline first (EDF) is a scheduling policy which uses a dynamic priority
scheme—it changes process priorities during execution based on initiation
times. As a result, it can achieve higher CPU utilizations than RMS. The EDF
policy is very simple: It assigns priorities in order of deadline. The
highest-priority process is the one whose deadline is nearest in time, and the
lowest priority process is the one whose deadline is farthest away.
19. Define preemption.
is the act of forcing a process out of execution i.e. making a context switch.
set of processes is un-schedulable and you need to guarantee that they complete
their deadlines, give possible ways to solve this problem?
The techniques available are as follows Get a
the processes to take less execution time Rewrite the specification to change
priority inversion problem?
inversion is a situation where in lower priority tasks will run blocking higher
priority tasks waiting for a resource. The two processes may deadlock.