January 2010 Preliminary Exams Computer Operating Systems (Questions 1-4)
... Describe how and the OS schedules read/write head of the disk. Explain the need for such
scheduling. Describe LOOK and C-LOOK disk scheduling algorithms. Give an example
of read/write head scheduling using these two algorithms. One of the algorithms results in
less read/write head movement. Name whi ...
CS 354 (Park) Midterm Oct. 19 (Mon.), 2015
... current (i.e., old) process that is context switched out, and retoring the state of the (new) process that is context
switched in. What is the sequence of steps performed—specify what each step does in words (i.e., no need to write
assembly code)—to save the state of the old process? Restoring the s ...
The following is reprinted from European Journal of Operational
... A.V. Naik, A. Baveja, R. Batta, and P. Caulkins, “Scheduling crackdowns on illicit drug
markets,” pp. 231-250, ©1996, with permission from Elsevier.
This paper presents an analytical approach for scheduling crackdowns on street-corner
drug markets. The crackdown scheduling problem is shown ...
... Scheduling (as an Optimization task):
How to best order the ready queue for efficiency purposes.
CPU utilization: % of time CPU in use
Throughput: # of jobs completed per time unit
Turnaround Time: wall clock time required to complete a job
Waiting Time: amount of time process is ready but waiting t ...
... c. Allot a longer amount of time to processes deserving higher priority, in other words,
have two or more quantums possible in the round-robin scheme. (Adaptive quantums for
each process. A higher priority process can use up to 2/3/4/etc.)
Question 4 [8 marks]. Explain the differences in how much th ...
... Levels 100-120: reserved for real-time threads.
Time-sharing threads are scheduled according to
their priority number and a logarithmic scale of 2.
• So a thread with a priority number greater by 2 is
four times as likely to be chosen to execute.
Windows XP - British Columbia Institute of Technology
... – Traditionally via motherboard with multiple processor slots
– Multiple processors are now incorporated into single
packages containing multiple ‘cores’
• Single core, dual core, quad core, etc..
– Individual processes, threads can run simultaneously on
Threads in Java
... Timed Waiting: sleeping for a specific
amount of time
Blocked: waiting for resources
Terminated: thread is complete
Processes and Threads
... A Race Condition may occur when
Two or more processes want to access a shared resource at
same time and the result depends upon who runs when.
CS 411 – Operating Systems II
... 3. Explain why synchronization is necessary for a concurrent processes scenario, and design
synchronization solutions (ABET Outcomes: A, J)
4. Apply appropriate algorithms to avoid deadlock for given concurrent processes (ABET
Outcomes: A, B, C, I, J)
5. Explain the strengths and weaknesses of sever ...
... Parallel – old and new run together
Direct cutover (or plunge) – replace the old system with new
Pilot – introduce to a small are of the organization
Phased – introduce in stages
... In the Resource Aware Scheduling, it is mentioned that it has
workload sensitive form of admission control. How does it
actually measure whether a given thread is near to complete ?
Template for project specification
... 1. A military base controls some remote devices whose feedback and reaction
time is critical. The devices are managed through some software programs.
Each program receives a signal from the device, elaborates the signal and
must reply within a certain time.
Criteria: Since feedback and reaction is c ...
... – Ability to mask access to memory, I/O or communication by
having another thread execute in the meantime (but how quickly
can execution switch between threads?)
... We’ve got thread basics worked out…
But it’s very helpful to understand how the
OS deals with thread scheduling
This lesson, we’ll work on scheduling threads
– understanding how each one gets executed
on the machine
RAL Tier 1a
... • Maui scheduler has been in production for
last 3 months.
• Allows extremely flexible scheduling with
many features. But ….
– Not all of it works – we have done much work with
developers for fixes.
– Major problem – MAUI schedules on wall clock
time – not CPU time. Had to bodge it!!
GNoC - Technion - Electrical Engineering
... Complete-exchange periodic traffic pattern.
No buffering, deflecting or dropping packets.
Equal propagation times and capacity on links.
Equal packet sizes.
Batch Processing and Timesharing
... OK for jobs such as payroll processing
Not OK for jobs such as airline reservations – cancellations
and reservations must be entered as they occur
In computing, scheduling is the method by which work specified by some means is assigned to resources that complete the work. The resources may be virtual computation elements such as threads, processes or data flows, which are in turn scheduled onto hardware resources such as processors, network links or expansion cards.A scheduler is what carries out the scheduling activity. Schedulers are often implemented so they keep all compute resources busy (as in load balancing), allow multiple users to share system resources effectively, or to achieve a target quality of service. Scheduling is fundamental to computation itself, and an intrinsic part of the execution model of a computer system; the concept of scheduling makes it possible to have computer multitasking with a single central processing unit (CPU).A scheduler may aim at one of many goals, for example, maximizing throughput (the total amount of work completed per time unit), minimizing response time (time from work becoming enabled until the first point it begins execution on resources), or minimizing latency (the time between work becoming enabled and its subsequent completion), maximizing fairness (equal CPU time to each process, or more generally appropriate times according to the priority and workload of each process). In practice, these goals often conflict (e.g. throughput versus latency), thus a scheduler will implement a suitable compromise. Preference is given to any one of the concerns mentioned above, depending upon the user's needs and objectives.In real-time environments, such as embedded systems for automatic control in industry (for example robotics), the scheduler also must ensure that processes can meet deadlines; this is crucial for keeping the system stable. Scheduled tasks can also be distributed to remote devices across a network and managed through an administrative back end.