Computer Organization Executing an Instruction popo Computer Organization

Computer Organization, Executing an Instruction popo

Computer Organization, Executing an Instruction • Fundamental Concepts • Processor fetches one instruction at a time and perform the operation specified. • Instructions are fetched from successive memory locations until a branch or a jump instruction is encountered. • Processor keeps track of the address of the memory location containing the next instruction to be fetched using Program Counter (PC). popo

Computer Organization, Executing an Instruction • Fetch the contents of the memory location pointed to by the PC. • The contents of this location are loaded into the IR (fetch phase). • IR ← [[PC]] • Assuming that the memory is byte addressable, increment the contents of the PC by 4 (fetch phase). • PC ← [PC] + 4 • Carry out the actions specified by the instruction in the IR (execution phase). popo

Computer Organization, Executing an Instruction popo

Computer Organization, Executing an Instruction • Type of instructions • Transfer a word of data from one processor register to another or to the ALU. • Perform an arithmetic or a logic operation and store the result in a processor register. • Fetch the contents of a given memory location and load them into a processor register. • Store a word of data from a processor register into a given memory location. • All operations and data transfers are controlled by the processor clock. popo

Computer Organization, Executing an Instruction • Register Transfers popo

Computer Organization, Executing an Instruction • Performing an Arithmetic or Logic Operation • The ALU is a combinational circuit that has no internal storage. • ALU gets the two operands from MUX and bus. • The result is temporarily stored in register Z. • What is the sequence of operations to add the contents of register R 1 to those of R 2 and store the result in R 3? – R 1 out, Yin – R 2 out, Select. Y, Add, Zin – Zout, R 3 in popo

Computer Organization, Executing an Instruction • Fetching a Word from Memory • The response time of each memory access varies (cache miss, memory-mapped I/O, …). • To accommodate this, the processor waits until it receives the requested operation has been completed (Memory-Function-Completed, MFC). • Move (R 1), R 2 • MAR ← [R 1] • Start a Read operation on the memory bus • Wait for the MFC response from the memory • Load MDR from the memory bus • R 2 ← [MDR] popo

Computer Organization, Executing an Instruction Execution of a Complete Instruction Add (R 3), R 1 Fetch the instruction Fetch the first operand (the contents of the memory location pointed to by R 3) • Perform the addition • Load the result into R 1 • • popo

Computer Organization, Executing an Instruction • Execution of a Complete Instruction • Add (R 3), R 1 popo

Computer Organization, Executing an Instruction popo

Computer Organization, Executing an Instruction • Layered view of a computer system • • The layered hierarchical view of the computer system illustrates how the operating system interacts with the users of the computer system: popo

Computer Organization, Executing an Instruction popo

Computer Organization, Executing an Instruction • A computer system can be divided into four components • Hardware • Operating System • Application programs • Users popo

Computer Organization, Executing an Instruction popo

Computer Organization, Executing an Instruction • Hardware: the CPU, the memory and the I/O devices • Provides the basic computing resources for the system • Application programs: - like word processors, spreadsheets, compilers, web browsers • Provides the way in which these resources are used to solve user’s problems • OS: controls and coordinates the use of the h/w among the various application programs for the various user • Users • The ultimate use of the computer is to provide one or set of applications • The user of these applications is called end users • Is not concerned with the computer architecture • User views a computer in terms of an application popo

Computer Organization, Executing an Instruction • That applications can be expressed in a programming language and is developed by an application progm • An application is a set of machine instructions that is completely responsible for controlling the h/w • Some of these prog are called utility prog such as • Management of files • Control of i/o • The most important system prog is called OS • Os masks the details of the h/w from the programmer and provide an interface with system • OS acts as a mediator making it easier for the programmer and for the application programs to access and use those facilities and services. popo