CS1251 Computer Architecture UNIT – 1 Basic Structure of Computers

Functional Units Computer Architecture- Encompasses the specification of an instruction set and the hardware units that implements the instruction. Functional Units - It consists of five functionally independent units, Input Output Arithmetic & Logical Unit Memory Control Unit

Functional Units Cont., Input Unit Output Unit Computer accepts coded information through input units, which reads the data. Ex) Keyboard,joysticks,trackballs ,mouse Output Unit It is an counterpart of the input unit. Its function is send to processed results to the outside. Ex) Printer

Functional Units Cont., Arithmetic and Logic Unit Most computer operations are executed here. Ex) Addition,Multiplication etc When operands are brought into the processor, they are stored in high speed elements ie) Register

Functional Units Cont., Memory Unit Its stores programs and data. The two types are Primary Storage Secondary storage Stored in the memory while they are being executed. Memory in which any location can be reached in a short and fixed time after specifying a address is called RAM The small, fast RAM called Caches. Primary storage is essential, its tends to expensive.

Functional Units Cont., Secondary Storage used when large amounts of data and many programs have to be stored. ex) Magnetic disks,tapes,Optical disk Input Output Memory Unit ALU Control Unit

Functional Units Cont., Control Unit Operation of Computer Sends control signals to other and senses their states. Operation of Computer Computer accepts information in the form of programs and data through input unit and stores it in the memory. Information stores in the memory is fetched, into arithmetic and logic init ,where it is processed. Processed information leaves the computer through an output unit. All activities inside the machine are directed by the control unit.

Basic Operational Concepts Example of Basic Operation is as:- Add LOCA,R0 this instruction adds the operand at memory location LOCA to the operand in a register in the processor,R0,and places the sum into register R0. Load LOCA,R1 Add R1,R0 the 1st instructions transfers the contents of memory location LOCA into processor register R1 and R0 and places the sum into R0.

Basic Operational Concepts Cont., Note that, this destroys the former contents of register R1 as well as those of R0,whereas the original contents of memory location LOCA are preserved.

Bus Structure Bus A group of lines that serves as connecting path for several devices. Additionally lines that carry the data,the bus must have lines for address and control purposes. Single Bus Structure Input Output Memory Processor

Bus Structure Cont., All Units are connected single bus. Main virtue is – low cost and its flexibility for attaching peripheral devices The devices to a bus vary widely in their speed of operations.ex) printer and keyboards are slow but magnetic and optical disks are faster. Buffer Register – a common approach, with the device to hold the information during transfers.

Software Performance System Software. – Collection of programs that are executed as needed to perform function such as Receiving and interrupting user inputs Entering and editing application programs Storing them as files in secondary devices Managing the secondary devices Controlling I/O units. Linking and running user written programs. Text Editor- Another important system program, it is used for entering and editing application programs.

Software Performance Cont., Operating Systems It is a software component, a collection of routines, that is used to control the sharing of and interaction among various computer units as they execute application programs.

Software Performance Cont., Important measure of the performance of a computer is how quickly it can execute programs. Elapsed Time – the total time required to execute the program. Processor time – the sum of these periods needed to execute the program.

Software Performance Cont., Processor Clock Processor signals are controlled by timing signal called a clock. Regular time intervals of clock called ,clock cycles. Clock rate R = 1/P clock per cycles. where P - one clock cycle Basic Performance Equation T= N*S / R

Software Performance Cont., Pipelining Overlapping the execution of successive instructions. ex) Add R1,R2,R3 Which adds the contends of registers R1 and R2 ,and places the sum into R3.The contends of R1 and R2 are first transferred to the inputs of the ALU.After the add operation is performed, the sum is transferred to R3.

Software Performance Cont., Clock Rate Two possibilities of increasing clock rate is, Improving the IC makes logic circuit faster Reducing the amount of processing done in done basic step Instruction Sets RISC-Stands for "Reduced Instruction Set Computing," and is pronounced "risk." It is arguably the fastest and most efficient microprocessor technology. CISC Stands for Complex Instruction Set Computing architecture used in the original Intel Pentium chips.

Software Performance Cont., Performance Measurement Measuring computer performance using benchmark Oraganisation called SPEC(System Performance Evaluation Corporation)- Selects and publishes different application domains SPEC Rating Running time of the reference computer ----------------------------------------------------------- Running time on the computer under test Overall SPEC Rating n (Π SPECi )1/n i=1

Instruction and Instruction Sequencing Four basic types of instruction operations are Data transfer between the memory and the processor registers Arithmetic and logic operations on data Program sequencing and control I/O transfers

Instruction and Instruction Sequencing Register Transfer Notation Transfer of information from one location to another location Ex) R1 [LOC] The contents of memory location LOC are transferd into processor register R1 Basic Instruction Types The statement C=A+B Add two variables A &B and stores the result in third variable C.

Instruction and Instruction Sequencing cont., One Address Instruction Operation source1,source2,Destination Add A add the contents of A Two Address Instruction Operation source, Destination Add A,B When the sum is calculated and result is stored in location B

Instruction and Instruction Sequencing cont., Three Address Instruction Operation source1,source2,Destination ex)Add A,B,C

Instruction and Instruction Sequencing cont., Instruction Execution And Straight line Sequencing Ex) C [A]+[B] Program Counter – which holds the address of the instruction to be executed next. Address of first inst must be placed into PC,then processor control to fetch and execute one at a time in order to increasing addresses.ie) straight line addressing

Instruction and Instruction Sequencing cont., Branching Task of adding list of n numbers Ex)Decrement R1 reduces the contents of R1 by each time through the loop. Branch instruction Load new value into the program Branch Target Processor fetches and executes the instruction at this new address

Instruction and Instruction Sequencing cont., Condition Codes Conditional branch instructions Four types are, N(negative)- set to 1 result is negative;otherwise cleared to 0. Z(zero) - set to 1 result is 0;otherwise cleared to 0. V(overflow) -set to 1 arithmatic overflow occure;otherwise cleared to 0. C(carry) -set to 1 carry out result;otherwise cleared to 0.

Addressing Modes Different ways in which location of an operand is specified in an instruction

Addressing Modes