GENERAL PURPOSE RESISTOR IN X86 ARCHITECTURE MICROPROCESSOR

The 8 GPRs are : 1. Accumulator register (AX) :Used in arithmetic operations. 2. Counter register (CX) :Used in shift/rotate instructions and loops. 3. Data register (DX) :Used in arithmetic operations and I/O operations. 4. Base register (BX) :Used as a pointer to data (located in segment register DS, when in segmented mode). 5. Stack Pointer register (SP) :Pointer to the top of the stack. 6. Stack Base Pointer register (BP) :Used to point to the base of the stack. 7. Source Index register (SI) :Used as a pointer to a source in stream operations. 8. Destination Index register (DI): Used as a pointer to a destination in stream operations. The order in which they are listed here is for a reason: it is the same order that is used in a push-to-stack operation. All registers can be accessed in 16-bit and 32-bit modes. In 16-bit mode, the register is identified by its two-letter abbreviation from the list above. In 32-bit mode, this two-letter abbreviation is prefixed with an 'E' (extended). For example, 'EAX' is the accumulator register as a 32-bit value. Similarly, in the 64-bit version, the 'E' is replaced with an 'R', so the 64-bit version of 'EAX' is called 'RAX'. It is also possible to address the first four registers (AX, CX, DX and BX) in their size of 16-bit as two 8-bit halves. The least significant byte (LSB), or low half, is identified by replacing the 'X' with an 'L'. The most significant byte (MSB), or high half, uses an 'H' instead. For example, CL is the LSB of the counter register, whereas CH is its MSB. In total, this gives us five ways to access the accumulator, counter, data and base registers: 64-bit, 32-bit, 16-bit, 8-bit LSB, and 8-bit MSB. The other four are accessed in only three ways: 64-bit, 32-bit and 16-bit. The following table summarises this : Register Accumulator Counter 64-bit RAX RCX 32-bit EAX ECX 16-bit AX CX 8-bit AH AL CH CL Register Data Base 64-bit RDX RBX 32-bit EDX EBX 16-bit DX BX 8-bit DH DL BH BL Register Stack Pointer Stack Base Pointer 64-bit RSP RBP 32-bit ESP EBP 16-bit SP BP 8-bit Register Source Destination 64-bit RSI RDI 32-bit ESI EDI 16-bit SI DI 8-bit