1. Basic Computer Organization
Architecture is defined as the science of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals.

2. Basic Computer Organization
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The block diagram of the computer system having the following three units, each functional unit corresponds to their basic operations,
Input Unit,
Central Processing Unit,
Memory Unit,
Output Unit.
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Input Unit
Input unit is used to send information or instructions or commands to the computer.
All input devices perform the following functions,
Accept data and instructions from outside world.
Convert it into a form that computer can understood.
Supply the converted data to the computer system for further processing.
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Input Devices:
The input received from the input unit is immediately stored in main memory and then processed.
Some of the input devices are:
Keyboard,
Mouse,
Trackball,
OMR (Optical Mark Recognizer)
MICR (Magnetic Ink character Recognizer)
BCR (Bar Code Reader)
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7. B) Central Processing Unit
It is the heart of the computer system, i.e all operations are carried out in this unit only.
It performs all calculations and it takes all decisions.
It controls all units of the computer.
It is subdivided into
Control unit
Register
Arithmetic and logical unit
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Control Unit
It instructs the computer how to carry out a program instructions.
It directs the flow of data between memory and arithmetic logical unit.
It controls and co-ordinates the entire computer system.
The input unit does not know when to receive data and where to put the data in the storage unit after receiving it.
the control unit instructs the input unit where to store the data after receiving it from user.
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Register
Special purpose, high speed temporary memory units.
Holds the type of information such as data, instruction, addresses and the intermediate result of calculation.
It works under the direction of control unit to accept, hold, transfer instruction or data and perform ALU comparisons at high speed.
Instruction addresses are normally used in consecutive registers and are executed sequentially.
Control unit reads an instruction in the memory by a specific address in the register and execute it.
Next instruction is then fetched from the sequence and executed and so on. 10 11
1000
1001
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Types of registers
Program Counter (PC) - Keeps track of next instruction to be executed.
Instruction Register (IR) - Holds the instruction to be decoded by the control unit
Memory Address Register (MAR ) - Holds the address of the next location in memory to be accessed.
Memory Buffer Register (MBR) - Used for storing data either coming to the CPU or data being transferred by the CPU.
Accumulator (ACC) - General purpose register used for storing temporary results and results produced by ALU.
Data Register (DR) - Used for storing the operands and other data.
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11. Arithmetic and Logical Unit
It executes all arithmetic and logical operations on the data made available.
Arithmetic operations like Addition, Subtraction, Multiplication and Logical operations such as comparisons are performed in ALU.
Consist of two units: Arithmetic unit and logic unit.
Arithmetic unit performing the actual computing and carrying out the arithmetic calculations such as addition, subtraction, multiplication and division and also perform these operations at a very high speed.
Logic unit: It enables the CPU to make logical operation based on the instruction provided to it.
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Memory Unit
Memory is that part of the computer that holds data and instruction for processing.
CPU requires memory to handle the intermediate result and to store the final output.
Memory can be classified into two types.
Primary memory (to handle data)
Secondary memory (to store the output)
Primary Memory
It is also called as main memory.
It stores and Provide information very fast.
The primary storage generally loses its contents when you switch off the computer. i.e., it is volatile in nature.
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It can be further classified into RAM (random access memory) and ROM (read only memory)
Secondary Memory
It is also known as auxiliary memory or external memory.
It is used for Storing instruction and data, since main memory is temporary and limited in size.
The memory is least, expensive and has larger storage capacity.
It is Non volatile in nature [information will not be lost even power is switched off.]
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Output Unit
Output unit is the communication between the user and the computer.
It provides the information and results of a computation to the outside world.
Commonly used output devices are:
VDU (Visual Display Unit)/ Monitor
Printer
Projector
Speaker
Plotter.
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