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Mid Term review
CSC345
• What is an Operating System?
• Various systems and their pros and cons
– E.g. multi-tasking vs. Batch
• OS definitions
– Resource allocator
– Control program
– Kernel
Abstract View of System Components
Important OS Features/services
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Process Management (CPU scheduling)
Main Memory Management
File Management
I/O System Management
Secondary Management
Networking
Protection System
Command-Interpreter System
OS Control Structure
Memory Tables
Process Image
Memory
I/O Tables
I/O
File
File Tables
Processes
Primary Table
Process 1
Process 2
…
Process N
User data
User program
System stack
PCB
Process State Diagram
dispatch
admit
New
Ready
Running
time-out
activate
release
event
wait
Suspend
Blocked
suspend
Exit
• System call vs. System program
Chapter 2: Computer-System
Structures
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Computer System Operation
I/O Structure
Storage Structure
Storage Hierarchy
Hardware Protection
General System Architecture
Two I/O Methods
Synchronous
Asynchronous
Dual mode operation & why ?
Use of A System Call to Perform
I/O
Use of A Base and Limit
Register
Hardware Address Protection
OS structure & Layered Approach
• The operating system is divided into a
number of layers (levels), each built on top
of lower layers. The bottom layer (layer
0), is the hardware; the highest (layer N) is
the user interface.
• With modularity, layers are selected such
that each uses functions (operations) and
services of only lower-level layers.
UNIX System Structure
Process Management
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Process vs. Thread creation
Process scheduling
Process Termination
Unix process creation fork() & exec()
– Identify parent vs. child
• How to find out process infomation
Process Control Block (PCB)
Process vs. Thread creation
Multithreading Models
• Many-to-One
• One-to-One
• Many-to-Many
---------------------------------------------• Pthread, JAVA thread, Kernel vs. User
thread
CPU Switch From Process to
Process
Process Scheduling Queues
• Job queue – set of all processes in the
system.
• Ready queue – set of all processes
residing in main memory, ready and
waiting to execute.
• Device queues – set of processes waiting
for an I/O device.
• Process migration between the various
queues.
Representation of Process
Scheduling
Schedulers
• Long-term scheduler (or job scheduler) –
selects which processes should be
brought into the ready queue.
• Short-term scheduler (or CPU scheduler)
– selects which process should be
executed next and allocates CPU.
• Midterm scheduler
Addition of Medium Term
Scheduling
Scheduling Criteria
• CPU utilization – keep the CPU as busy as possible
• Throughput – # of processes that complete their
execution per time unit
• Turnaround time – amount of time to execute a particular
process (finishing time – arrival time)
• Waiting time – amount of time a process has been waiting
in the ready queue
• Response time – amount of time it takes from when a
request was submitted until the first response is
produced, not output (for time-sharing environment)
Class Exercise
Each team works on finding an average turnaround time for a
quantum time at 1, 2, 3, 4, 5, 6, 7
Process
p1
P2
P3
p4
Time
6
3
7
1
First-Come, First-Served (FCFS)
Scheduling
ProcessBurst Time
P1
24
P2
3
P3
3
P
P
Parrive in
• Suppose that
the processes
the
order: P1 , P2 , P24
3
0
27
30
The Gantt Chart for the schedule is:
1
2
3
Turnaround Time Varies With The
Time Quantum
Context Switch
• When CPU switches to another process,
the system must save the state of the old
process and load the saved state for the
new process.
• Context-switch time is overhead; the
system does no useful work while
switching.
• Time dependent on hardware support.
User program & Kernel interface
Note: This picture is excerpted from Write a Linux Hardware Device Driver, Andrew O’Shauqhnessy, Unix world
Two I/O Methods
Synchronous
Pooling or
interrupt
Asynchronous