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COMS 261
Computer Science I
Title: Computer Organization
Date: September 2, 2005
Lecture Number: 3
1
Announcements
• Office hours for today 9/2/05
– 1:30pm – 3:00pm
• Read
– Chapter 1, start chapter 2
2
Review
• Computing Terminology
– Computer systems
– Measurements
– Positional number systems
3
Outline
• Computing Terminology
– Decimal to binary conversion
• Octal
• Hexidecimal
– Programming
• High-Level language
• Assembly language
• Machine Language
– Think – Edit – Compile - Test Cycle
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Operating System
• Windows®, UNIX®, Mac OS X®
• Controls and manages the computing
resources
– Important services provided by an operating
system
• File system
– Directories, folders, files
Operating System
– Commands that allow for manipulation of the
file system
• Sort, delete, copy
– Ability to perform input and output on a
variety of devices
– Management of the running systems
Decimal to Binary Conversion
• Convert 1110  ?2
• Procedure
– Find the highest power of the base (2) the
number will divide
• Find the highest power so that the base raised
to that power is less than or equal to the given
number
5
4
2 2
32 16
3
2
8
2
4
2
1
2
2
0
2
1
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Decimal to Binary Conversion
• 24 = 1610 is larger than 1110, while
• 23 = 810 is less than or equal to 1110
– There is a 23 in the binary representation of the
number 1110
– Subtract the base raised to the highest
power from the number to convert
1110  810  310
1110  1* 2  ...
3
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Decimal to Binary Conversion
– Find the highest power of 2 the remainder
will divide
• 22 = 4 is larger than 310
– There is not a 22 in the binary representation of 1110
• 21 = 2 is less than or equal to 310
– There is a 21 in the binary representation of 1110
1110  1* 2  0 * 2  1* 2 ...
3
2
1
– Subtract the base raised to the highest
power from the remainder
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Decimal to Binary Conversion
310  210  110
1110  1* 2  0 * 2  1* 2 ...
3
2
1
– Find the highest power of the base (2) the
remainder will divide
• 20 = 1 is the same as 110
– There is a 20 in the binary representation of 1110
1110  1* 2  0 * 2  1* 2  1* 2
3
2
1
0
10
Decimal to Binary Conversion
– Subtract the base raised to the highest
power from the remainder
• No remainder, and no more powers of 2,
therefore
110  110  010
1110  10112
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Other Representations
• There are other representations of
quantities
– Octal: base 8
– Hexadecimal: base 16
• Conversions between the
representations
– Similar to binary to decimal and decimal to
binary conversion, but with a different base
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Two’s Complement
•
•
•
•
Used by almost all computers
Binary representation
Includes negative numbers
Contains one representation for the
quantity 0
• Arithmetic operations
– Simpler to perform
– Result in a two’s complement number
• No extra conversion must take place
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Programming
• Programs are specific sequences of
instructions
– Instructions are primitive operations
• Move data from one place to another
• Add two items together
• Check a value for equivalence to zero
•…
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Programming
– Instructions have a binary representation or
encoding
– Instruction set
• The set of legal instructions for a particular
machine
– MIPS
– Intel
– AMD
• Legal bit patterns recognized by the machine
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Programming
10110010 10100110 01001110 11001010
• May mean (for the MIPS processor)
– Add the contents of two registers
– Put the result in a third register
• May not be a part of the instruction set for the
Intel processor
– Illegal instruction
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Programming
• It is possible to write a program in binary
instructions
10110010 10100110 01001110 11001010
11100011 10000100 01001010 11011001
10001001 11100101 11011000 10011011
.
.
.
– The binary instruction set is also called
machine language
• Varies from processor to processor
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Programming
• Do software developers write programs
in machine language?
– NO
• Tedious
• Error prone, single bit out of place
• Specific to only one machine
– Said to be not portable
• Difficult to maintain and change
• Impossible for someone else to work on the
program
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Machine Language
• Programs written using the binary
instruction set are said to be written in
machine language
– The resulting list of instructions is called
machine code, also called object code
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Assembly Language
• Assembly language
– A language directly related to machine
language
– Each instruction has a unique symbol
(mnemonic) associated with it
– Assembly language programmers use the
symbols that represent instructions instead
of binary instructions
– An assembler converts the symbols into
machine language (instructions)
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Assembly Language
• Example assembly language program
mnemonics
push
mov
sub
mov
mov
mov
mov
mov
mov
mov
leave
ret
ebp
ebp,esp
esp,0x8
eax,0xcccccccc
dword ptr [esp],eax
dword ptr [esp+0x4],eax
dword ptr [ebp-0x4],0x6
eax,dword ptr [ebp-0x4]
dword ptr [ebp-0x8],eax
eax,0x0
arguments
near
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Assembly Programming
Editor
Think
Think
Think
Assembly
Language
Program
Assembler
Machine
Language
Program
Different Input
Test Cases
Execute (run)
Program
22
Programming
• Machine language
– Low-level programming
– Binary language
• Assembly language
– Higher-level programming
• Still pretty low-level
– Mnemonics simplify programming
23
Programming
• Assembly language
(Cont.)
– Simpler than machine language
• Still tedious
• Error prone
• Not portable
• Difficult to maintain assembly code program
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HLL Programming
• High-level languages
– More English like
– Powerful constructs
– Simpler to write and maintain code
– More portable
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HLL Programming
• High-level languages
(Cont.)
– Popular high-level languages
•C
• C++
• Java
• Fortran
• Perl
• Smalltalk
• Scheme
•…
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HLL Programming
• Code reusability
– Many operations are common to most
programs
• Printing to the console (screen) or a file
• Mathematical routines
• String processing
• Etc, …
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HLL Programming
• Code reusability
(Cont.)
– Most useful to have common routines
already compiled into machine language
(object code)
– Libraries are the object code for groups of
related routines packaged into a single file
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HLL Programming
• Code reusability
(Cont.)
– Libraries and different object files must be
combined forming a single executable file
• Linking and the linker
– Linking is the process of combining
different files of object code into a single
executable file
– The linker is a program that performs the
linking
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HLL Programming
C++/Fortran
Language
Program
Editor
Compiler
Assembly
Language
Program
Math
Library
Object
Code
Linker
Assembler
Think
Think
Think
Machine
Language
Program
Execute (run)
Program
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IDE’s
• Integrated Development Environments
– Provides one user interface for the
development process
• Editor, Compiler, Linker, Loader, Debugger,
Viewer
– We will be using the CodeWarrior IDE
throughout this course
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