Архитектура системы. Архитектура набора команд Распределение функций, реализуемых системой, между ее уровнями.
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adding the contents of memory locations A and B
The Arithmetic and Logic Unit (ALU)
The ALU implements a variety of operations
The list of operations the ALU can perform is referred to as the Instruction Set
Different CPUs implement different Instruction Sets
Computers use the Fetch Execute Cycle to execute instructions
The Fetch-Execute Cycle
At a generic level, computers use a Fetch-Execute Cycle
PC = Program Counter (stores the address of the next instruction to be executed)
IR = Instruction Register (stores the instruction to be executed)
AC = Accumulator (General Purpose Register)
Memory is 16 bits long.
1 = Local memory address to Accumulator
5 = Add value in memory address to Accumulator,
2 = Store value in accumulator to memory address
A simple example of how this is implemented
The list of instructions that a CPU can execute are called the Instruction Set
Obviously, CPUs implement different types of Instructions
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- (IN, OUT)
(JC, JZ, REP)
(EMMS, MOVQ, ..)
Different Instruction Sets are classified by size of their instruction
Consider the difference in coding the Expression
A=(B x C) + D
When using three Address instruction, A = (B X C) + D
Mult B,C,A//A = B x C
ADD D,A,A//A = A + D
Two Address Instruction
Load B,A\\ A = B
Mult C,A\\ A = A x C
Add D,A\\A = A + D
When using one address instruction, a special register on the CPU called the Accumulator is used. The Accumulator implicitly stores the results of operations
Load B\\ Acc = B
Mult C\\ Acc = Acc X C
Add D\\ Acc = Acc + D
Store A\\ A = Acc
. , . CISC-, omplexInstructionSetComputers. , , Intel 80x86 Motorola 68000. , , RISC-, ReducedInstructionSetComputers. RISC-: DEC Alpha, Power PC, IntelItanium.
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