Computer Architecture CST 250 Microprocessor Registers Prepared by:Omar Hirzallah

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

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

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

C.P.U Registers

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

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.

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

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