Computer Architecture And Organization UNIT-II General System Architecture

Contents  Store program control concept  Flynn’s classification of computers (SISD, MISD, MIMD)  Multilevel viewpoint of a machine: digital logic, micro architecture, ISA, operating systems, high level language digital logic, micro architecture, ISA, operating systems, high level language  Structured organization; CPU, caches, main memory, secondary memory units & I/O;

What is a Computer? A device that accepts data, processes the data in accordance with a stored program, generates results, and usually consists of input, output, storage, arithmetic, logic, and control units A device that accepts data, processes the data in accordance with a stored program, generates results, and usually consists of input, output, storage, arithmetic, logic, and control units

Block Diagram of Digital Computer Random-access memory (RAM) Central processing unit (CPU) Input-output processor (IOP) Input devices Output devices Block diagram of a digital computer

Block Diagram of Digital Computer A digital computer consists of a number of processors interconnected with memory and Input/Output devices A digital computer consists of a number of processors interconnected with memory and Input/Output devices A Processor or CPU (Central Processing Unit) fetches instructions from memory, and executes them one after another A Processor or CPU (Central Processing Unit) fetches instructions from memory, and executes them one after another A Memory is where programs and data are stored A Memory is where programs and data are stored I/O devices allow for interaction between users and computer (printers, keyboard, mice… ) I/O devices allow for interaction between users and computer (printers, keyboard, mice… )

Computer Architecture And Organization Organization is how features are implemented Organization is how features are implemented physical aspects of computer systems. physical aspects of computer systems. attributes of a system visible to a programmer: instruction set, data types, I/O mechanisms, addressing of memory attributes of a system visible to a programmer: instruction set, data types, I/O mechanisms, addressing of memory e.g., circuit design, control signals, memory types. e.g., circuit design, control signals, memory types. Architecture is those attributes visible to the programmer Architecture is those attributes visible to the programmer Logical aspects of system as seen by the programmer. Logical aspects of system as seen by the programmer. hardware details transparent to a programmer: operational units and their interconnections, peripheral interfaces, memory technology hardware details transparent to a programmer: operational units and their interconnections, peripheral interfaces, memory technology E.g., instruction sets, instruction formats, data types, addressing modes. E.g., instruction sets, instruction formats, data types, addressing modes.

Computer architecture = Computer architecture = Instruction set architecture Instruction set architecture + Machine organisation Machine organisation

Instruction Set Architecture Instruction set architecture is the attributes of a computing system as seen by the assembly language programmer or compiler. This includes Instruction set architecture is the attributes of a computing system as seen by the assembly language programmer or compiler. This includes Instruction Set (what operations can be performed?) Instruction Set (what operations can be performed?) Instruction Format (how are instructions specified?) Instruction Format (how are instructions specified?) Data storage (where is data located?) Data storage (where is data located?) Addressing Modes (how is data accessed?) Addressing Modes (how is data accessed?) Exceptional Conditions (what happens if something goes wrong?) Exceptional Conditions (what happens if something goes wrong?)

Machine Organization Machine organization is the view of the computer that is seen by the logic designer. This includes Machine organization is the view of the computer that is seen by the logic designer. This includes Implementation, Capabilities & performance characteristics of functional units (e.g., registers, ALU, shifters, etc.). Implementation, Capabilities & performance characteristics of functional units (e.g., registers, ALU, shifters, etc.). Interconnections of these units Interconnections of these units Information flows between these units Information flows between these units Control of information flow i.e.Logic and means by which such information flow is controlled Control of information flow i.e.Logic and means by which such information flow is controlled Typically the machine organization is designed to meet a given instruction set architecture. Typically the machine organization is designed to meet a given instruction set architecture.

Design better programs, including system software such as compilers, operating systems, and device drivers. Design better programs, including system software such as compilers, operating systems, and device drivers. Optimize program behavior. Optimize program behavior. Evaluate (benchmark) computer system performance. Evaluate (benchmark) computer system performance. Why study computer architecture and organization?

Computer Evolution First Generation: Vacuum Tubes First Generation: Vacuum Tubes ENIAC (Electronic Numerical Integrator and Computer) ENIAC (Electronic Numerical Integrator and Computer)  John Mauchly and John Eckert ( )  Decimal number system  Memory: 20 registers  30 tons, 1500 Sq Ft, 18,000 vacuum tubes  5000 additions per second John von Neumann helped crystallize the idea; proposed the von Neumann Machine John von Neumann helped crystallize the idea; proposed the von Neumann Machine

EDVAC (Electronic Discrete Variable Automatic Computer) EDVAC (Electronic Discrete Variable Automatic Computer)  Stored-program computer ( )  Prototype for general-purpose computers  Binary data representation  Main memory (data and instructions)  ALU & CU  Input/Output Computer Evolution

The Von Neumann machine The model for almost all conventional processor architectures. Comprises: A Memory containing a numbered sequence of cells (words) referenced by their addresses (Linear Store) A Memory containing a numbered sequence of cells (words) referenced by their addresses (Linear Store) An ALU (Arithmetic Logic Unit) to perform operations (program steps) using temporary storage cells (registers) An ALU (Arithmetic Logic Unit) to perform operations (program steps) using temporary storage cells (registers) A Control Unit to ensure an ordered sequence of instructions is presented to the ALU A Control Unit to ensure an ordered sequence of instructions is presented to the ALU

The Stored Program Concept The stored program concept was proposed about fifty years ago; to this day, it is the fundamental architecture The stored program concept was proposed about fifty years ago; to this day, it is the fundamental architecture Von Neumann’s proposal was to store the program instructions right along with the data. Von Neumann’s proposal was to store the program instructions right along with the data.

The Von Neumann Architecture

Memory (k x m) array of stored bits (k is usually 2 n ) (k x m) array of stored bits (k is usually 2 n ) Address Address unique (n-bit) identifier of location unique (n-bit) identifier of location Contents Contents m-bit value stored in location m-bit value stored in location Basic Operations: Basic Operations: LOAD LOAD read a value from a memory location read a value from a memory location STORE STORE write a value to a memory location write a value to a memory location

Interface to Memory How does processing unit get data to/from memory? How does processing unit get data to/from memory? MAR: Memory Address Register MAR: Memory Address Register MDR: Memory Data Register MDR: Memory Data Register To read a location (A): To read a location (A): 1. Write the address (A) into the MAR. 2. Send a “read” signal to the memory. 3. Read the data from MDR. To write a value (X) to a location (A): To write a value (X) to a location (A): 1. Write the data (X) to the MDR. 2. Write the address (A) into the MAR. 3. Send a “write” signal to the memory. MEMORY MAR MDR

Processing Unit Functional Units Functional Units ALU = Arithmetic and Logic Unit ALU = Arithmetic and Logic Unit could have many functional units. some of them special-purpose (multiply, square root, …) could have many functional units. some of them special-purpose (multiply, square root, …) Registers Registers Small, temporary storage Small, temporary storage Operands and results of functional units Operands and results of functional units Word Size Word Size number of bits normally processed by ALU in one instruction number of bits normally processed by ALU in one instruction also width of registers also width of registers PROCESSING UNIT ALUTEMP

ALU and the data-path the internal part of the internal part of the CPU is also called data- path it consists of registers and the ALU it consists of registers and the ALU The ALU performs simple arithmetical/logic operations (ADD, AND,OR) The ALU performs simple arithmetical/logic operations (ADD, AND,OR) It takes its operands from the registers and store the result back in them It takes its operands from the registers and store the result back in them The process of reading operand and storing result back is called data-path cycle The process of reading operand and storing result back is called data-path cycle The faster the data-path cycle is the faster the computer runs The faster the data-path cycle is the faster the computer runs A B ALU A+B A B input register registers output register

Control Unit Orchestrates execution of the program Orchestrates execution of the program Instruction Register (IR) contains the current instruction. Instruction Register (IR) contains the current instruction. Program Counter (PC) contains the address of the next instruction to be executed. Program Counter (PC) contains the address of the next instruction to be executed. Control unit: Control unit: reads an instruction from memory reads an instruction from memory the instruction’s address is in the PC the instruction’s address is in the PC interprets the instruction, generating signals that tell the other components what to do interprets the instruction, generating signals that tell the other components what to do an instruction may take many machine cycles to complete an instruction may take many machine cycles to complete CONTROL UNIT IR PC

Instruction The instruction is the fundamental unit of work. The instruction is the fundamental unit of work. Specifies two things: Specifies two things: opcode: operation to be performed opcode: operation to be performed operands: data/locations to be used for operation operands: data/locations to be used for operation An instruction is encoded as a sequence of bits. (Just like data!) An instruction is encoded as a sequence of bits. (Just like data!) Often, but not always, instructions have a fixed length, such as 16 or 32 bits. Often, but not always, instructions have a fixed length, such as 16 or 32 bits. Control unit interprets instruction: generates sequence of control signals to carry out operation. Control unit interprets instruction: generates sequence of control signals to carry out operation. Operation is either executed completely, or not at all. Operation is either executed completely, or not at all. A computer’s instructions and their formats is known as its Instruction Set Architecture (ISA). A computer’s instructions and their formats is known as its Instruction Set Architecture (ISA).

Input and Output Devices for getting data into and out of computer memory Devices for getting data into and out of computer memory Each device has its own interface, usually a set of registers like the memory’s MAR and MDR Each device has its own interface, usually a set of registers like the memory’s MAR and MDR Some devices provide both input and output Some devices provide both input and output disk, network disk, network Program that controls access to a device is usually called a driver. Program that controls access to a device is usually called a driver.