1. Computer Architecture CST 250
Microprocessor Registers
Prepared by:Omar Hirzallah

2. Contents General Purpose Registers Index Registers Segment Registers
Special Registers
Programming Languages

3. The Registers in CPU C.P.U Registers
Processor uses a very high speed small in size memory device during data processing which are called registers
C.P.U Registers
General Purpose Registers
Index Registers
Segment Registers
Special Registers
Accumulator
Base
Count
Data
Stack Pointer
Base Pointer
Source Index
Destination Index
Code Segment
Data Segment
Stack Segment
Extra Segment
Instructions Pointer
Flags Register

4. General Purpose Registers:
Accumulator (AH, AL, AX, EAX):
It accumulates the results from mathematical calculations and can be used for data movement. AH 8 bits, AL 8 bits, AX 16 bits, EAX 32 bits
Base (BH,BL,BX, EBX): It points to memory locations and it can be used for data movement and arithmetic. (Points to data in the Data Segment) BH 8 bits, BL 8 bits, BX 16 bits, EBX 32 bits
Count (CH, CL, CX, ECX): This counter is used typically for loops. It can be automatically incremented or decremented. CH 8 bits, CL 8 bits, CX 16 bits, ECX 32 bits
Data (DH,DL, DX, EDX): It is used in calculations. It is also used significantly for multiply / divide operation. DH 8 bits, DL 8 bits, DX 16 bits, EDX 32 bits

5. C.P.U Registers

6. INDEX REGISTERS:
Stack Pointer (SP, ESP): It points to the location of the stack (points to the end of the stack). SP 16 bits, ESP 32 bits
Base Pointer (BP, EBP): It is also used to point inside the stack. It is used to access the sub routine data. BP 16 bits, EBP 32 bits
Source Index (SI, ESI): It is used for string operations (points to the source). SI 16 bits, ESI 32 bits
Destination Index Register (DI, EDI): It is used for string operations (points to the destination). DI 16 bits, EDI 32 bits

7. SEGMENT REGISTERS (ALL 16 bits)
Code Segment (CS): It points to the memory area where program's instructions are stored.
Data Segment (DS): It points to the memory area where program's data is stored.
Stack Segment (SS): It points to the memory area where stack is stored.
Extra Segment (ES): It can be used to point to additional data segments, if necessary.

8. SPECIAL REGISTERS: SPECIAL REGISTERS:
Instruction Pointer (IP, EIP): It points to the next instruction that the processor is going to execute. (also called program counter)
Flags Register (Flag, Eflag): It contains individual bits set by different operations.
CF  Carry
OF  Overflow
ZF  Zero
SF  Sign

9. Programming Languages:
There are basically two types of programming languages:
High Level Languages
(Pascal, Basic, Cobol, C, Fortran etc.)
Low Level Languages
(Assembly)
Each processor has a set of assembly instructions called “Instruction Set”.
CISC stands for Complex Instructions Set Computers
RISC stands for Reduced Instructions Set Computers
Assembly Language Assembler Machine Language