Chapter 10 Instruction Sets: Characteristics and Functions Suzy Hanko

1. Chapter 10 Instruction Sets: Characteristics and Functions Suzy Hanko

2. Machine Instructions • Machine instructions are the instructions executed by the processor. • These determine what the processor will do • Inside the computer, each instruction is represented as a series of bits. • Because this is difficult to remember, symbolic representation is common.

3. Elements of Machine Instructions • Operation code (opcode): Tells the processor which operation to perform • Source operand reference: tells the processor where the operands can be found • Result operand reference: Tells the processor where to store the result • Next instruction reference: Tells the processor where to fetch the next instruction from • Not all elements are used in every instruction

4. Types of Instructions • Four main types of instructions: • Data processing: Arithmetic and logic • Data storage: Moving data between registers and memory locations • Data movement: Transferring data and programs to memory or the user • Control: Tests the value of data and/or branches to a different set of instructions

5. Transfer of Control • This is when the next instruction performed is not the one that immediately follows the current one in memory. • Branch/Jump: jumps to an instruction other than the next one in sequence. • Skip: skips the next instruction in sequence • Procedure call: executes a procedure before coming back and executing the next instruction

6. Types of Operands • Four main types of operands: • Numbers • Characters • Logical data • Addresses • The actual names and exact effects of the operands varies between machines

7. Call/Return Instructions • These instructions call and return from functions. • Four Instructions in x86 architecture: Call, Enter, Leave, and Return • When a function is called must push the return point and frame pointer onto the stack, then move the frame pointer to a new frame and place the stack pointer in that frame.

8. Condition Codes • Condition codes set status flags, which are set by certain operations and used in conditional branch instructions. • Each status flag, and some combinations of status flags, can be tested as a condition for a jump.

9. Stacks • A stack is a LIFO (last-in-first-out) data structure • A stack (called the run-time stack) is used to manage procedure calls and returns, and variables.

10. Stacks (continued) • To operate the stack, three addresses are needed to be kept in registers: • The stack pointer, which contains the address of the top of the stack. • The stack base, which contains the address of the bottom of the reserved block. • The stack limit, which contains the address of the top of the reserved block.

11. Little- and Big-Endian • There are two main ways to store numbers in a computer • Big-endian stores the most significant byte in the lowest numerical address, similar to the way we write numbers • Little-endian stores the most significant byte in the highest numerical address • Both styles have advantages and disadvantages, with neither being better on average.