Instruction Set Architecture

The basic differentiation in the type of internal storage in a processor. The major choices of architecture are,

            ~Stack

            ~Accumulator

            ~Set of  Register

Operands may be named explicit or implicit.

STACK

            The operands in a stack architecture are implicit on the top of stack.The code of sequence for C=A+B is,

                                    Push A

                                    Push B

                                    Add

                                    Pop C

Here,The top of stack register,points to the top input operandswhich is combined with the operand below.The first operand is removed from the stack ,the result takes the place of the second operand.The TOS is updated to print the result. All operands are implicit in it.

ACCUMULATOR

            The operands in an accumulator architecture are implicit. the code of sequence for C=A=B of Accumulator is,

                                    Load A

                                    Add B

                                    Store C

Here,The first operand is load into Accumulator.The second operand from memory to Add instruction and the result is store in accumulator. so that input operand and result is both an implicit

SET OF REGISTER           

            The set of register is general purpose register architecture have only explicit operands, either register or memory location. The classes of register,                  

• Register to Memory Architecture
• Load to store Architecture
• Memory to Memory Architecture

Register to Memory Architecture

            This class can access memory as part of any instruction is called Register to Memory Architecture. The code of sequence for C=A+B is,

                                    Load R1,A

                                    Add R3,R1,B

                                    Store R3,C

Here,The first input operand is a register and another input is in memory and the result goes to a register. The add instruction has explicit operands.

Load and store Architecture

            This class can access memory only with load and store instruction is called load and store Architecture.The code of sequence for C=A+B is,

                                    Load R1,A

                                    Load R2,B

                                    Add R3,R1,R2

                                    Store R3,C

Here,All operands are register and is like the stack architecture

Memory to Memory Architecture

• This class keeps all operands in memory is called a memory to memory architecture.
• Instruction with multiple memory operands per typical ALU instruction

            The major reason for using the General Purpose Register computer are twofold.

• The register are faster than memory
• The register are more efficient for a compiler to use than other form          of storage.

TYPES  AND  SIZE OF OPERANDS

·          The data can be annoted with tags that are implemented by the hardware. These tags specify the type of operand and the operation.

TYPES OF OPERANDS	SIZE OF OPERANDS
Integer Charater Half word Word Single precision floating point Double precision floating point	16 bits 8 bits 16 bits 32 bits 32 bits 64 bits

OPERATION IN THE INSTRUCTION SET

·                     All architecture is that the most widely executed instruction are the simple operation of an instruction set. For example,

OPERATOR TYPE	EXAMPLES
Arithmetic and Logical	Integer arithmetic and logical operation : add,subtract,multiply,divide,AND,OR
Data transfer	Loads- stores(move instruction on computer with memoryaddressing)
Control	Branch,jump,Procedure call and return, traps.
System	Operating system call,virtual memory management instruction.
Floating point	Floating point operations : add, multiply, divide,compare.
Decimal	Decimal add, Decimal multiply,decimal to character conversion.
String	String move, string compare, String search.
Graphics	Pixel and vertex operations, compression/decompression Operation

·         Hence, the implementor of these instruction should be sure to makethese fast,as they are the common case.

·         This instruction are found in every computer for every application of desktop,servr,embedded with the variation of operation is largely depending on instruction set.