Computer Architecture : Lecture 2
Computer Architecture :
The First Commercial Success : Study Case
Instruction Groups
We all know that computer works with the help of instructions. We have divided the different instructions in different groups, for better understanding. Their name are as follow
1. Data Movement instructions
a. Deals with data movement from memory to processor or processor to memeory
b. Deal with movement from register to register ot from register to memory / processor
2. Arithmetic / Logic Instructions
a. Deals with mathematical function ( + , – multiply ) or logical functions (and, Xor)
3. Program Control Instruction
a. We know normally the instructions are carried out one by one (consecutively) . However some times we do not need to run consecutive instruction. For these purposes , such commands are use (You man like to think about command “if”)
4. Special instructions
a. They are used to force processor to change its behavior as per our will
DATA MOVEMENT Instructions
Mov ax,bx ; move data from bx to ax
Lda 0246 ; load 0246 to accumulator
Arithmetic Instruction
Add ax,1234 Add 1234 with ax
Add bx,ax add ax to bx
Add bx,[1212] add data from address and add it to bx
Program Control
Cmp ax,0 compare ax with 0
Jne 1234 jump if not equal to the instruction and mov at address 1234
Special Instruction
Cli disable interrupts
The First Commercial Success : Study Case
Model : IBM PC
Reason : Easily available platform , and free software available to program
Processor: IAPX88 (Intel Advance Processor 88)
This was the first processor that was implanted on a IBM system. It was the first commercial success. Later on intel released IAPX 38086
IAPX88 was a 16 bit microprocessor.
Intel created 4 bit processors , however the first 8 bit processor by intel was 8080. Later on a advance version 8085 was introduced, which was 8 bit processor but had more computational power as compared to its ancestors
The 8088 had a 1 MB memory , which was a big achievement. The first IBM Machine had 4.1 Mhz , which was considered a high speed.
In this case study we will have a look at intel IAPX architecture. The processor is a 16 bit processor. First of all we will have look at its general purpose registers .
The registers were named as AX,BX,CX,DX
Register Architecture
| General Purpose registers | Pointer Index Base Register | Flag Register | Segment Register |
| AX
BX CX DX |
SI
DI |
CS
DS SS ES |
General Purpose Register
AX : Accumulator Register
AX
| 8 Bit | 8 Bit |
| AH | AL |
Al= A low side
Ah A High side
Hence you can use this as 16 bit register or as two 8 bit register.
BX : Base Register –> Used to Access Memory
CX : Counter Register –> It is used where we need to count special instruction
DX : Destination Register –> Destination of I/O
INDEX BASE REGISTER
//16 bit register
SI–> Holds memory addresses for source
DI–>Holds memory addresses for destination
IP–>Instruction Pointer (Used in program while accessing memory)
SP–>It will be discussed in later (used while accessing memory)
BP –>Base pointer
Flag Register
C=Carry Bit // Holds carry after addition
P=Parity Bit// used for parity checking (w.r.t number of 1s )
A=Auxiliary Carry // We already know that 4 binary bits group together to create a hexadecimal number called “NIBBLE”. While doing addition /subtraction if one group of nibble produces carry for next group of nibble such carry is called auxiliary carry
Z=Zero bit // The Z bit is set (1) if last mathematical or logical operation produces zero in result .
S=Sign bit // The most significant bit represents the sign (1= ive)
T=Trap flag // pending
I= Interupt flag // Either we need interrupt or not to effect our program
D= Direction Flag // While copying memory , do we need to copy contents from up to down or down to up
O=Over flow = used in signed arithmetic
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