1. Computer organization & Assembly Language Programming
Rabie A. Ramadan

2. Class Style Do not think of the exam Feel free to stop me at any time
Just think of the class materials and how much you learn from it
Feel free to stop me at any time
I do not care how much I teach in class as long as you understand what I am saying
There will be an interactive sessions in class
you solve some of the problems with my help
Chapter 2 — Instructions: Language of the Computer — 2

3. When the time is up , just let me know….
Chapter 2 — Instructions: Language of the Computer — 3

4. Textbook
S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.

5. Grading

6. Course Objectives
To introduce basic concepts of computer organization.
To illustrate the computer organization concepts by Assembly Language programming.
To teach Assembly language of most recent processor such as Intel Pentium processor.

7. Outline Why program in assembly language?
Time-efficiency
Space-efficiency
Accessibility to hardware
Typical applications
Why learn assembly language?
Performance: C versus assembly language
Multiplication example
A user’s view of computer systems
What is assembly language?
Relationship to machine language
Advantages of high-level languages
Faster program development
Easier maintenance
Portability

8. What is a Machine ?
Process
Directives
Raw
Material
Final
Product
Machine
In General: Device that processes a series of raw materials into the desired product following a well-defined process

9. Types of Machines Device Raw Material Products Computer Data
Food Processing Factory
Natural Fruits, Vegetables, Meats, Dairy and Spices
Manufactured (Packaged) Food Products
Airport
Planes, Travelers, Goods
Administrative Office
Application Files
Decisions
Computer
Data

10. Computer Machine Model
Machine = Computer
Process = Program
Directives
Program = Suite of
Instructions
Instruction = Simple Operation

11. Basic Computer Organization (1)
Central Processing Unit (CPU)
Need a Unit to Execute Instructions
Need a Unit to Contain Programs
Need a Unit to Contain Input Data
Need a Unit to Contain Intermediate Stage Data
Need a Unit to Input Data
Need a Unit to Output Data
Memory IO

12. Basic Computer Organization (3)
Memory
Cpu
I/O
Buses
Buses: Groups of Electrical Signals or Wires That
Establish The Communication Between The
Different Computer System Components

13. Memory Similar to a set of Storage Bins Data 1 Data 2 11 2
Data 1
Data 2
Each Bin is Called:
A Memory Location
Each Location has a Content
And an Index
The Content is The Data
and the Index is The Address
Data is Written in Memory
And Read from The MEmory
The CPU Reads Data From Memory
And Writes Data Into Memory

14. Basic Computer Organization (3)
Memory
Cpu
Address Bus
Data Bus
I/O
Control Bus
Address Bus: Specifies the Address of the Data being Accessed
Data Bus: Carries the Data to be Transferred
Control Bus: Specifies the Nature of the Transfer:
(Memory Read/Write or I/O)

15. Memory 2n Storage Device
Stores Programs and Data coded in binary format.
Technically “similar” to a two-dimensional array of “switches”
A “switch” called a bit (abbr. for binary digit)
n Address lines means 2n words of m bits each 2n n
Address m 1
Data

16. Memory
2 Operations:
Read: Copy Data stored in word of Address (on Address lines) to Data Bus
Write: Store Data on Data Bus into word of Address (on Address lines) n
Memory
Addr
Read
Write m
Data
COE 205

17. Concept of Address It is an index in the memory
It represents a “geographic” location of a word in the memory
Number of Address lines and Word size determine Memory Capacity (Size)
Most of the time:
Memory size = 2n words = 2n * m bits
COE 205

18. RAM RAM: Random Access Memory
Although the name is about the way memory is accessed. Historically, volatile memory has been called RAM.
Volatile (do not retain information on power off)
Used mainly as Central Memory for CPUs
Two types of RAM
Static: Continuous Retention of Information
Dynamic (DRAM): needs refresh cycle to maintain information
COE 205

19. ROM
Non Volatile
Used to store data (programs) that do not change often (fixed)
Many types
Mask ROM: Values set at fabrication stage. Values cannot be changed
Fuse PROM: Values set at burning phase. Values cannot be changed
EPROM: Can be erased (UV)
EEPROM: Electrically erased
Flash EEPROM: Easily reprogrammable.
New: NVRAM (Non Volatile RAM): Fast access time.

20. Disk Drives
Hard Drive: suite of magnetic disks. Mechanically read and write data by moving a set of magnetic head over the disks
CD-ROM, DVD-ROM: Suite of optical disks read by measuring the time of laser reflexion between “1” and “0” N S
“1”
“0”

21. Program Execution A Program is a suite of instructions
Program Execution is Sequential
Program is stored in Memory
Program is executed by CPU
Instruction 1
Instruction 2
Instruction 3
Instruction n
COE 205

22. CPU Executes Programs Stored in Memory
Executes Instructions ONE by ONE
Only “knows” instructions: Instruction Set
DO NOT know any notion of Program as a single entity.
Everything is a suite of instructions
COE 205

23. CPU Structure (1) Is Mainly a Data Processing Unit Controlled
by a Control Unit.
Data Processing Unit: Datapath
Registers (Scratch pad working space or temporary data storage)
ALU: Arithmetic and Logic Unit
Internal Buses
Control Unit: Generates Commands to “drive” Datapath operations
COE 205

24. CPU Structure (2) Control Unit Datapath ALU Register Register
Data Path is Similar to a Pipe Structure where valves are controlled by the Control Unit
Control Unit
Datapath
ALU
Register
Register
COE 205

25. Master Clock Instructions Executed step by step
Need a “Rhythm” Generator to move forward in the steps:
Time
Clock Cycle
Clock Frequency = 1/Clock Cycle Period : MHz
Every CPU needs a Clock to control the transition from one execution step to the next
COE 205

26. Instruction Set Instruction Set is the Catalog of the CPU
Defines what are ALL the possible operations that the CPU can execute
Only Instructions are recognized by CPU.
CPU does NOT “understand” High Level Language (text).
CPU understands instructions coded in numbers called machine code.
COE 205

27. Instruction parameters
Each Instruction specifies an action or a suite of actions:
Action(s) “identifier” or Operation Code or Opcode
Action arguments or operands
Methods specifying how to access the operands, called addressing modes
Instruction specified as:
<Opcode> <Operand 1, addr_mode1> <Operand 2, addr_mode2> ….
COE 205

28. Number of Operands Many types of Instruction Sets
Instruction Set with One Operand: Implicit Register Called Accumulator. Everything goes to and from the accumulator:
Instruction Set with Two Operands: Many registers can be used as accumulators
Instruction Set with Three Operands: Mainly Register Based.
COE 205

29. Fetch – Decode - Execute
Address
of next Instruction
Cpu
Memory
Fetch
Fetch
Instruction
Read Command
Opcode
Reg
Immediate
Decode
Instruction
Decoder
Decode
Execute
Execute
COE 205

30. Address of Programs Where the Address of next instruction is Stored ?
Need for an Instruction Pointer
Called: “Program Counter” PC
Critical Component of CPU
Conveniently useful for changing program sequence (Branch instructions)

31. Instruction Register
Where is the current instruction going to be stored during its execution ?
Need for a Register
Called: “Instruction Register”
Data Bus
Critical Component of CPU
Internal Register. Cannot be used (accessed) by instructions
Holds the current instruction until its execution is completed
Tightly Coupled to the decoding portion of the control unit
Connected to the datapath (to transfer operand fields)
Opcode
Op1
Op2
Instruction Decoder

32. Program in Memory Binary code (machine code). Memory (8-bit) B8 00
MOV AX,5 05 03
ADD AX,BX C3 EB
JMP Next E7

33. High Level Languages Machine independent.
Cannot be run directly on the target machine
Need to be translated to machine language
Compiler: program that translates a HLL program to a machine language program of a specific platform
The Machine language program produced by the compiler is the executable program.
Translating HLL programs to machine language programs is not a one-to-one mapping
A HLL statement translated to one or more machine language instructions
Usually, machine language programs produced by compilers are not efficient
Deals with Data types (integer, real, complex, user-defined) vs. machine language: no data types only binary words.
COE 205

34. Assembly Language Text version of machine language
Human friendly representation of machine language
Based on mnemonics (easy to memorize abbreviations of actions) instead of dealing with opcode numbers.
Complicated format simplified with some conventions
Text file translated into machine code by the Assembler
COE 205

35. Assembler
Program that assemble the programs written in assembly language into machine language
Because there is a ONE to ONE mapping between instructions written in assembly language and machine language instructions, the process is called: assembly rather than translation.
Disassembly (reverse process) is also easy because of the ONE to ONE relation between the assembly language instructions and the machine language instructions
MOV DX, 1
MOV AX, BX
MOV AX, CX
MOV AX, DX
ADD AX, 1
ADD AX, 2
ADD AX, BX
ADD AX, CX
ADD AX, i
SUB AX, 1
SUB AX, BX
ADD AX, 1234h
BA 0001
8B C3
8B C1
8B C2
83 C0 01
83 C0 02
03 C3
03 C1
83 E8 01
2B C3
COE 205

36. Linker
Program used to link together separately assembled/compiled programs into a single executable code
Allows the programmers to develop different parts of a large program separately, test them separately and ‘freeze’ them for future use.
Allows the programmer to develop store portions of programs that have been intensively tested and used into a “program library” for anyone to re-use them.
Produces modular programs and greatly enables the management of large programming projects

37. Debugger/Monitor
These are tools that allow the assembly programmers to:
Display and alter the contents of memory and registers while running their code,
Perform disassembly of their machine code (show the assembly language equivalent),
Permit them to run their programs, stop (or halt) them, run them step-by-step or insert break points.
Break points: Positions in the program that if are encountered during run time, the program will be halted so the programmer can examine the memory and registers contents and determine what went wrong.

38. A User’s View of Computer Systems

39. What Is Assembly Language?
Some example assembly language instructions:
inc result
mov class_size,45
and mask1,128
add marks,10
Some points to note:
Assembly language instructions are cryptic
Mnemonics are used for operations
inc for increment, mov for move (i.e., copy)
Assembly language instructions are low level
Cannot write instructions such as
mov marks, value
MIPS Examples
andi $t2,$t1,15
addu $t3,$t1,$t2
move $t2,$t1

40. What Is Assembly Language? (Cont’d)
Some simple high-level language instructions can be expressed by a single assembly instruction
Assembly Language C
inc result result++;
mov class_size,45 class_size = 45;
and mask1,128 mask1 &= 128;
add marks,10 marks += 10;

41. What Is Assembly Language? (Cont’d)
Most high-level language instructions need more than one assembly instruction
C Assembly Language
size = value; mov AX,value
mov size,AX
sum += x + y + z; mov AX,sum
add AX,x
add AX,y
add AX,z
mov sum,AX

42. What Is Assembly Language? (Cont’d)
Readability of assembly language instructions is much better than the machine language instructions
Machine language instructions are a sequence of 1s and 0s
Assembly Language Machine Language
(in Hex)
inc result FF060A00
mov class_size,45 C7060C002D00
and mask, E0080
add marks, F000A

43. What Is Assembly Language? (Cont’d)
MIPS examples
Assembly Language Machine Language
(in Hex)
nop
move $t2,$t A2021
andi $t2,$t1, A000F
addu $t3,$t1,$t A5821

44. Why Program in Assembly Language?
Two main reasons:
Efficiency
Space-efficiency
Time-efficiency
Accessibility to system hardware
Assembly code tends to be compact
Assembly language programs tend to run faster
Only a well-written assembly language program runs faster
Easy to write an assembly program that runs slower than its high-level language equivalent

45. Typical Applications
Application that need one of the three advantages of the assembly language
Time-efficiency
Time-convenience
Good to have but not required for functional correctness
Graphics
Time-critical
Necessary to satisfy functionality
Real-time applications
Aircraft navigational systems
Process control systems
Robot control software
Missile control software

46. Performance: C versus Assembly Language
C version
AL version
Last slide