The architecture of computer hardware and systems software an information technology approach ch15p1

Chapter 15 – Part 1
The Internal Operating System
The Architecture of Computer Hardware and
Systems Software:
An Information Technology Approach
3rd Edition, Irv Englander
John Wiley and Sons 2003


OS Internals – Part I
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Process Scheduling
CPU Scheduling
Memory Management
Virtual Storage

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Target Model

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Loading and Executing a Program
Network Services
Translates logical file
requests

File management

IOCS (I/O control system)

Device management /
Resource allocation

Load programs into MM
Allocates execution time
Provides overall system
control
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Memory management /
Scheduling
Monitor
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Multi-Tasking System
 The OS must allocate resources (CPU,
memory, I/O) to multiple processes
 Different scheduling routines are used for
different objectives

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Processes
 Process: basic unit of work in the OS
 A program together with all the resources that are
associated with it as it is executed
 Program: a file or listing
 Process: a program being executed

 Independent vs. cooperating processes
 PID (process ID): a unique identifier for each
process
 Process creation: user vs. system
 Forking, spawning, cloning a new process
 Parent and child processes

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Process Control Block
 A block of data for
each process in the
system
 Contains all relevant

information about the
process
 Typical process
control block on the
right 
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Two Processes Sharing a
Single Program

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Process States
 Three primary process operating states
 Ready state
 Running state
 Blocked state

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Dispatching - Move from ready state to running state

Wake-up - Move from blocked state to ready state
Time-out - Move from running state to ready state
Process completion
 killed, terminated, destroyed

 Additional states – suspend, swap
 Resumption – Move from suspended state to ready
state

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Process State Diagram

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Threads
 ‘Miniprocess’ that can be run independent of
other parts of the process
 Event-driven programs
 No control blocks
 Shares resources allocated to its parent process
including primary storage, files and I/O devices

 Advantage of process/thread families over

multiple independent processes:
 Reduced OS overhead for resource allocation and
process management
 Substantially less information than a normal PCB

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CPU Scheduling
High-level scheduling
Short-term scheduling
(dispatcher)
Mid-level scheduling
I/O scheduling

Chapter 15

Adding a program to the pool of
programs to be executed
Deciding which process shall be
executed next by the processor
Swapping processes
Deciding which process’s pending
I/O request shall be handled by an
available I/O device

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Dispatching Objectives
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Maximize throughput
Minimize turnaround time
Maximize CPU utilization
Maximize resource allocation
Promote graceful degradation
Provide minimal and consistent response time
Prevent starvation

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Nonpreemptive Dispatching
 First in, first out (FIFO)
 Unfair to short processes and I/O based
processes
 Shortest Job First (SJF)
 Longer jobs can be starved
 Priority Scheduling

 Dispatcher selects among jobs with the
same priorities
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Preemptive Dispatching
 Round robin
 Inherently fair and maximizes throughput

 Dynamic Priority
 Based on ratio of CPU time to total time process has been in
the system
 Smallest ratio has highest priority
 Linux, Windows 2000

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Preemptive Dispatching
 Multilevel feedback queues
 Favors short jobs, I/O bound jobs
 Each level assigns more CPU time

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Memory Management
 Memory Partitioning
 Fixed
 Variable


Best fit, first-fit, largest-fit algorithms

 Memory fragmentation

 Overlays
 Programs are divided into small logical pieces for
execution
 Pieces are loaded into memory as needed

 Memory Relocation
 Addresses have to be adjusted unless relative
addressing is used

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Memory Overlays

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Virtual Memory
 Virtual memory increases the apparent
amount of memory by using far less
expensive hard disk space
 Provides for process separation
 Demand paging
 Pages brought into memory as needed

 Page table
 Keeps track of what is in memory and what is still
out on hard disk
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Frames and Pages
Program

Memory

Unit

Page

Frame

Address

Logical

Physical

Size

2 to 4KB

2 to 4KB

Amount

# of bits in
Installed memory
instruction word

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Frames and Pages

Binary Paging

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Dynamic Address Translation

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Page Table
Page Frame
1
2
3
4
5
6
7
8
9
10
11

6
4

Pages not in main memory:
page fault when accessed

8

10
1
2

Disk

1

2

3

4

5

6

7

8

9

10 11

7

Swap space
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Virtual Memory Pages

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Steps in
Handling a
Page Fault

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Locality of Reference
 Most memory references confined to small
region
 Well-written program in small loop, procedure or
function
 Data likely in array and variables stored
together
 Working set
 Number of pages sufficient to run program normally,
i.e., satisfy locality of a particular program
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