Computer Architecture & Organization

Computer Architecture
- is the study of the components that make up a computer system and how they are interconnected.

Computer Organization
- is concerned with the implementation of a computer architecture.


General purpose (revised Von Neumann) architecture




Functions:

Processor
- executing instruction
- processing the data
- components: control unit, register set, and arithmetic/logical unit

Memory
- where data reside

Control Unit
- fetches the instruction from the memory or I/O devices place it in a queue
- update the program counter
- also decodes the fetched instruction into binary form
- performs the address translation
- controls the timing of all computer operations according to the system clock

System bus
- acts as the bridge for the processor and other components for them to communicate

Internal bus
- acts as the subway within the processor for the other components to communicate

ALU
- where arithmetic and logical operation is processed

Register Set
Segment register
- used as base location address for instruction

Code segment (CS)
o holds the base location for all executable instruction (code) in a program

Data Segment (DS)
o base location for variables


Stack Segment (SS)
o holds the stack base location

Extra Segment (ES)
o additional base location


Pointer Register
- contain the offset of data instruction

Instruction pointer
o contains the offset address of the next instruction to be executed
o associated with CS

Base Pointer (BP)
o contains an assumed offset from SS
o used by subroutine to locate variables
o associated with DS

Stack Pointer (SP)
o contains the offset of the top of the stack
o SS and SP combine to form a complete address of the stack


General Purpose Register
- data registers
- used for arithmetic and data movement

AX (accumulator)
o arithmetic operations

BX (base)
o hold addresses of a procedure or variable

CX (counter)
o a counter for repeating or looping instruction

DX (data)
o a special role in multiply and divide operation


Index Register
- contain the offset of data instructions

Source Index (SI)
o source string is pointed to by SI

Destination Index (DI)
o acts as the destination for string movement instruction


Flags Register

O = overflow
- indicate overflow of the left most bit

D = direction
- determine left or right direction for moving or comparing data

I = interrupt
- indicate that all interrupts to be processed or ignored

T = trap
- permit operation of the processor in single-step-mode

S = sign
- indicate the resulting sign of an arithmetic or comparison operation 0 (negative), 1 (positive)

Z = zero
- indicate the resulting value if 0 (nonzero), 1 (zero)

A = auxiliary carry
- contain a carry out of bit 3 on 8 bit data

P = parity
- indicate even or odd parity, 0 (disparity), 1 (parity)

C = carry
- contain leftmost bit


Bit = 0 or 1
Byte = 8 bits
Word = 2 bytes or 16 bits

Representation of nonnumeric data

ASCII – American Standard Code for Information Interchange

A – Z (41h – 5Ah)
a – z (61 – 7Ah)
0 – 9 (30h – 39h)

EBCDIC – Extended Binary – Coded Decimal Interchange Code

A – I (C1h – C9h)
J – R (D1h – D9h)
S – Z (E2h – E9h)
a – i (81h – 89h)
j – r (91h – 99h)
s – z (A2h – 9h)
0 – 9 (F0h – F9h)