Transcript OperatingSystemLectures - Ferdowsi University of Mashhad

Operating System Concepts and Techniques
Lecture 1
Background: hardware concepts review
M. Naghibzadeh
Reference
M. Naghibzadeh, Operating System Concepts and Techniques, iUniverse publisher, first ed. 2011.
To order: www.iUniverse.com, www.barnesandnoble.com, or www.amazon.com
Introduction
Computer: a device which runs programs
Program: a set of instructions to do a specific task
Operating system: an essential program which sits on top of
the computer hardware; acts as an interface between the running
program and the computer hardware to:



Provide basic software modules to be used by programs
Facilitate efficient use of computer resources
Prevent running programs undesirable interferences
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Computer Hardware Organization
Essential Units are:





Control unit,
Arithmetic-logic unit,
Cache memory,
Main memory
Other devices
 Input/Output devices
 Network connectivity

Figure 1 shows essential logical
interconnections
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Logical interconnctions of devices
CPU
Control Unit
Arithmetic-Logic
Unit
Input
Unit
Main
Memory
Output Unit
Figure 1: Computer organization model
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Bus-base connection vs point to point
Bus-based reduces interconnection wiring

Similar to a highway via which different parts of a city are connected.
There are at least three busses, address bus, data bus and
control bus
Some computer devices are not directly connected to the
computer’s internal bus
In a 32-bit computer, for example, the address bus and data bus
are each 32 bits wide
There are mechanisms for possessing the address and data
buses, otherwise data and addresses from different devices
could become mixed up
A model of the bus-based computer organization is shown in
Figure 2.
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Essential Physical interconnctions of a computer’s
devices
Central
Processing Unit
(CPU)
Main
Memory
(MM)
Monitor
Mouse
Control bus
Address bus
Data bus
Hard Disk
(HD)
Internet
Connection
...
Figure 2: A bus-based Computer organization model
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The Fetch-Execute Cycle
Reading an instruction from main memory (RAM) and
moving it to the CPU


Program counter (PC) points to the instruction to be fetched
The instruction is moved to Instruction Register (IR) in the
Central Processing Unit (CPU)
Finding out what has to be done with respect to this
instruction
and
perform
the
actions,
i.e.,
microinstructions
Repeats this cycle of moving an instruction from the
main memory to the CPU and executing it, over and
over again.
This is called Fetch-Execute Cycle
See Figure 3
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The Details of Fetch-Execute Cycle
Fetch cycle
Read the instruction pointed out
by the Program Counter (PC)
register from main memory and
move it to the CPU
Find out what this instruction is
Execute cycle
Move the data upon which the
instruction has to be executed from
main memory to the CPU.
Execute the instruction, i.e.,
perform what is requested by the
instruction. Perhaps this may
readjust the PC.
Adjust PC for the next instruction
Figure 3: A simplified functional model of a computer
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Program Counter (PC) update
How is PC filled?
When the computer is started or restarted, it is
automatically filled with an initial value by the hardware
 The operating system will fill the PC with the first executable
instruction of the new program
 Otherwise, it is updated through fetch-execute cycle
The next instruction to be fetched is most likely the one
immediately following this instruction


However, this is not always the case. Look at the piece of program below
that is written in a pseudo code format.
1. If A > B
2. then print A
3. else print B
4. endif
Most of the time, the PC update during the fetch cycle suffices

Sometimes, its content is modified by the execution of the instruction
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How is fetch-excute cycle Brocken?
Will find out in Lecture 2
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BIOS boot process
The need for BIOS
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Main memory, cache, and internal registers are volatile
Upon turned on, the computer starts the fetch-execute cycle
With volatile memories, at start, there is no instruction in RAM
Therefore, BIOS is stored in a Read Only Memory (ROM)

This program is called Basic Input Output System
At start or restart, the BIOS address is automatically loaded
into the PC thus facilitating its being run
BIOSs are produced by many factories, but perform the same
basic functions.
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BIOS Actions at start/restart
Power-On Self Test

checks to make sure every immediately required
device is connected and functional
BIOS manufacturer’s logo display

Compaq, Phoenix, Intel, IBM, Award plus, or any
other manufactures
CMOS and setup modifications

The Complementary Metal Oxide Semiconductor
memory is a battery-supported memory which keeps
modifiable information like date, time, computer
password…
Loading boot strap of the operating system
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Operating System installation
OS is giant and cannot be stored in a ROM
In addition, we would like computers to be flexible to
run any operating system
Therefore, the OS has to be installed after the
computer is manufactured
During installation, it is transferred from say DVD to
the fastest disk drive
During the transfer other functions such as
decompression and initialization is performed. This
process is called OS installation
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Booting the operating system
At any start/restart begin the process of loading the operating system
BIOS transfers one block of data from the first valid bootable device to
the main memory.
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The block is taken from a fixed place of the (block one of track zero) and is put in a
specific and fixed place of main memory (0xFC00)
The size of the block of data is usually 512 bytes
The block contains General data about the device + the
bootstrap program
After loading the bootstrap, PC is filled with start of bootstrap
This little program will complete the boot process, perhaps by initiating
other phases
The BIOS will then become a passive program which can be used by
the operating system to perform many operations
BIOS contains many other useful procedures, especially for interacting
with input/output devices
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Kernel
Eventually, essential parts of the operating system
will be loaded in main memory
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This includes the Operating system Kernel
Kernel is the essential part, or the inner part, of the seed of
an operating system
Other parts are usually loaded on demand
Kernel is composed of:


many routines for doing activities that are not be performed
by any single machine instruction
In addition, kernel is composed of many essential processes
(threads or agents), each designed to carry out a
responsibility of the operating system
Kernel routines are built using machine instructions
and/or BIOS functions
Kernel is protected
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Our computer looks like
Other layers of the OS
OS Kernel
System BIOS
…
Computer Hardware
(Bare Machine)
“Layer 0”
…
“Layer 1”
“Layer 2”
Figure 4: A four-layer machine with system BIOS, kernel, and processes
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An actual hierarchical OS
System Services/User Applications: Service Controller, Remote Procedure Call, C++ Compiler, Environmental Subsystems
(Posix, OS/2, Win32), etc.
Input/ Output
Manager
Virtual Memory
Manager
Device Drivers
Process/ Thread
Manager
Security
Reference
Manager
Cache
Manager
Windows
Manager
Windows 2000 Kernel
Hardware Abstraction Layer (HAL)
Hardware and Hardware Interfaces: Buses, CPU, Main Memory, Cache, I/O Devices, Timers, Clock, Direct Memory Access,
Interrupts, Cache Controller, etc.
Figure 5: The structure of Windows 2000
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Modes of operations
Every computer has at least two modes of operation:


Kernel mode, or supervisor mode. All machine instructions,
whether privileged or non-privileged, are executable in this
mode of operation
User mode. Privileged instructions are not usable
One of the most remarkable features of any operating
system is the way mode transfer is made possible.
During the system startup the system is in kernel
mode
Right after the startup the mode changes to user
mode
When a program calls a routine of the kernel the
mode automatically changes to kernel and in return
from the routine, the mode changes back to user
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Making Your Own Operating System
With our current knowledge, it is impossible to
write an actual operating system

However, by thinking of making a little operating
system tremendous knowledge is learned
Follow the following steps in writing your own
little, do nothing useful, operating system
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Making Your Own Operating System…
1. Using a running computer, write a mini program to do something
over and over again
1.
2.
3.
I would prefer this program to repeatedly display the word “Hello”
on computer monitor
Make the size less than 512 bytes. This program will be your
operating system
Use any language but compile it and produce the executable file
2. An executable file has two sections:
1.
2.
The file header, i.e., metadata, say 512 bytes
The actual machine language instructions, say 512 bytes, i.e., a “com” file
3. Write a program to transfer the “com” file to sector one of track
zero of a diskette
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Making Your Own Operating System…
4.
5.
Prepare a simple bootable device such as diskette
Transfer the “com” file to sector one of track zero of the
diskette
1.
6.
7.
You have successfully stored your operating system on the
diskette
Reset the computer and enter the BIOS setup/modify
program. Make the first floppy drive be the first bootable
device
Insert your own operating system diskette into the first floppy
drive of the computer and reset the computer again. Wait until
your operating system comes up
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Summary
The following subjects were discussed:
Computer, Program, and operating system
Logical Computer organization, physical
organization, functional organization model
and the Fetch-Execute Cycle
The need for BIOS, BIOS actions, Installing
the OS, Booting the OS
Operating system Kernel, hierarchical
structure, modes of operation
How to make your own small OS
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Find out
Your computer’s instruction categories based on
their length
The benefits of adjusting the PC register during the
fetch cycle even though we have to readjust it
during the execute cycle for some instructions
For a 32-bit computer, the maximum memory size
that the CPU can directly address (without using a
base register)
Your computer’s speed in terms of MIPS
The company which built your computer’s BIOS
The source code of a BIOS from the Internet
A source code for a small OS from the Internet
How to make the above source code actually work
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Any Question?
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