Input, Output and Processing


Chapter: 2 Input, Output and Processing

Computer systems consist  of the following hardware components:

  • Input devices accept data or commands in a form useable by computers. Data and commands can also be sent to the processing unit; e.g., keyboards, mice, scanners, microphone, digital camera.
  • Output devices display the processed information understandably and usefully; e.g. printers, monitors, speakers.
  • Processing devices are contained in a computer’s system unit and are comprised of circuitry. The main circuit board is the motherboard, with its central processing unit (CPU) and memory.
  • Storage devices include secondary storage for data and programs outside the computer’s processing unit; e.g., hard disk drives, Zip drives, CD- ROM and DVD-ROM drivers. Drivers read from and write to storage media (the physical material that can store data and programs).
  • Communication devices provide connections between computers and communication networks, allowing for exchange of information and data with other computers via transmission media such as cables, telephone lines, and satellites.

Central Processing Unit

Central Processing unit (CPU) is the main components or “brain” of a computer, which of performs all the processing of input data. Its Function is to fetches examine and then execute the instructions stored in the main memory of a computer. In microcomputers, the CPU is built on a single chip or Integrated Circuit (IC) and is called as a Microprocessor. The CPU consists of the Following district Parts.

a)Arithmetic Logic Unit (ALU)
b)Control Unit (CU)
1)Arithmetic Logic Unit:
The arithmetic and logic unit of CPU is responsible for all arithmetic operations like addition, subtraction, multiplication and division as well as logical operations. Such as less than, equal to and greater than. Actually, all calculations which are stored in main memory of computer are transferred to ALU for Processing. After Processing many times data move from ALU to memory and vice-versa.
2)Control Unit;
The control unit is responsible for controlling the transfer of data and instructions among other units of a computer it is considered as the “Central various system” of a computer, as it manages and coordinates all the units of the computer. It obtains the instruction from the memory, interprets then and directs the computer it (obtain) operation of the computer .It also performs the physical data transfer between memory and the periphery devices
Registers are small high speed circuits (memory locations)
Which are used to store data, instructions and memory address. Registers can store one word of data (1 word= 2 bytes & 1 byte= 8 bits, Details of bits & bytes. Until it is overwritten by another word. Depending on the processors capability the number and type of registers vary from one CPU to another. Registers can be divided into six categories viz. General purpose Registers, Pointer Register, Segment Register, Index Register, Flags Register and Instruction Pointer Register, depending upon their functions.
Types of Registers: There are five types of Registers.
General Purpose Registers: – The 8086 microprocessor has Four 16- bit general purpose registers.
  • AX Registers;- It is the primary accumary accumulator used for operations involving 1/o and arithmetic functions. The high bits of AX are called AH and low bits of AX are called AL.
  • BX Register:- It is the basic register used as an index for external addressing and computing. It has 2 parts –BH and BL
  • CX Register;- It is the count register mainly used to control the number of times of loop is executed. It has 2 parts – DH and DL
  • DX Register:- It is the data register used for 1/o and multiple/divide functions involving large values. It has 2 parts – DH and DL
  • Segment Register:- They contain address of each segment. There are Four segment register in 8086.
  • CS Register:-  It contains  starting address of a program’s code segment [Segment that contains machine instructions to be executed]. Its offset value [distance from segment’s starting address] is stored in Instruction Pointer (IP) register.
  • DS Register:– It contains the starting address of a program’s data segment [ Segment that contains data & work areas]. Its offset value is stored in Source Index (SI) register.
  • SS Register:– It  contains the starting address of a program’s stack segment [ segment that contains temporally stored data]. Its offset value is stored in Stack Pointer (SP) register.
  • ES Register:- It is an extra segment register that contains starting address of a character data. Its offset value is stored in Destination Index (DI) register.
         Pointer Register:- These registers are used to access data in stack segment. There are three types of register.
  • Stack Pointer (SP) Register:- It is used to store offset value of data stored in stack segment. 
  • Base Pointer (BP) Register:- It facilitates referencing parameters of which are data address passed to the stock.
  • Instruction (IP) Register:-   It can contains the offset value of instruction stored in program’s code segment.
Index Register:- They are used for indexed addressing. There are two index registers in 8086.
Source Index (SI) Register:- It is used or string operation. It is associated with DS register.
Destination Index (DI) Register:- It is also used or string operation. It is associated with ES register.
Flag Registers:-  They indicate some condition produced by the execution of an instruction. They also control certain operation of the execution unit. They are of following two types.
Conditional Flag Registers:- They are set by some conditions generated as a result of lost arithmetic/ logical instruction execution unit. They are six conditional flag registers.
  1. CF (Carry Flag):-  It is set when a carry is generated.
  2. PF (Parity Flag):– It is set when result has even parity.
  3. AF (Auxilliarly Flag):- It is set when a carry is generated out of 3 bits on eight bit data.
  4. ZF (Zero Flag):- It is set when result is zero.
  5. SF (Sign Flag):– It is set when result is negative.
  6. OF (Overflow Flag):– It is set when there is an overflow of result.
Control Flag Registers:-  They are set /reset by programmer to control the operation of execution unit. There are three control flag registers.
  1. TF ( Single-Step Trap Flag):-  It permits operation of processor in single step mode. For Example: DEBUG Command of DOS set TF.
  2. IF(Interrupt Enable Flag):-  It is set when there is an external interrupt in the execution of program.
  3. DF ( String Direction Flag):–  It designates direction ( left or right) for moving or comparing strings. 
                                                                                                                                                     Data Bus                                                                                                                                   Control Bus
Used to send address of the memory on 1/0 part.                                     Used to sent data among various devices                             .             Used to control the various device of a microcomputer.
This data is unidirectional as most of times CPU generates address.   This bus is bidirectional as data travels in both directions      .      This bus is also bi-direction.
Clock is another important component of CPU which measures and allocates a fixed time slot for processing each unit and every micro operation [ smaller functional operation]. In simple terms CPU is allocated one or more clock cycles to complete a micro-operation. CPU execute the instructions in synchronization with the clock pulse. 
The clock speed of CPU is measured in terms of Mega Hertz (MHz) or millions of cycle per second. The clock speed of CPU varies from one model to another in the range of 4.77 MHz [ in 8088 processor] to 266 MHz [ in Pentium II]. CPU speed is also specified in terms of millions of Instructions per second (MIPS) or Million of Floating Point Operations Per second (MELOPS) (MELOPS).
Parallel Machines: A  computing machine having many ALUS our CPU’S
Which operate in parallel is called a parallel machine. According to MJ Flynn there are following three categories of parallel machines.
SISD:- Single Instruction single data stream.
SIDM:-Single Instruction multiple data stream
MIMD:-Multiple Instruction multiple data stream
                        Lets us discuses about these in details
A.SISD:- This machine has on instruction stream and one data stream. In this machine instruction are fetch from memory execute by single CPU 1BY1 the tradional von navmann machine is an SISD machine the SISD machine has limited features of parallel. Some machines have multiple ALUS each of which programs. A single operations some machines have a CPU consisting of multiple processing units each of which execute a spirit instruction each time interval such machines are called pipe line machines.
B.SIMD:– This machine has one instruction streams and multiple data stream. Parallel machines a computing machines having  many AIUS our CPUS . In this machine multiple data sets are executed by a single CPU by two approach, the ALU is a vector as result. This category of computer is called Vector Machine. In other approach, the machine consists of a square grid of processor and Memory elements. Each unit of processor users its own data stored in its own memory. Such machines are called Array Machines.
C.MIMD:– This machine has multiple instruction stream and multiple data streams. In these machines, different Instruction sets either sharing a common memory or using their own local memories. An MIMD machine is also called a multiprocessing system.
                                                                                 A multiprocessor with shared memory.
                                                                             A multiprocessor with Local memory.
     Multiprocessing System:- A system is computer system have several CPUs, which execute program in parallel. There are many type of organization of a multiprocessing system.
  • In some multiprocessing system , several  CPU work together to do the main processing. Incase of break down of one CPU, other CPUs perform its function.
  • In some system, each CPU is assigned a specific type of function
  • In some system several CPUs from a client/server type of network. The main CPU of server is called the back-end processor while CPUs of  client are called front-end processor.