The document discusses the history and components of computers. It introduces the Turing model which defined a computer as a programmable machine that can perform any computation given the appropriate data and program instructions. The von Neumann model expanded on this by describing the major components of modern computers: the central processing unit, memory to store both data and program instructions, and input/output components. A computer is thus defined as a device that can accept data as input, process it based on program instructions stored in memory, and produce output, with hardware and software working together to perform these functions.

1. Introduction to Computers

2. What is a Computer?
• A computer is an electronic device that
operates under the control of a set of instructions
that is stored in its memory unit.
• A computer accepts data from an input device
and processes it into useful information which it
displays on its output device.
• A computer is a collection of hardware and
software components that help you accomplish
many different tasks.

3. A Typical Computer System

4. Functional Components of a Computer
INPUT
UNIT
OUTPUT
UNIT
MAIN MEMORY
CENTRAL
PROCESSING
UNIT

5. Input Unit
• The input unit is formed by the input devices attached to
the computer.
• Input devices accept data in a form that the computer
can utilize.
• It sends the data or instructions to the processing unit to
be processed into useful information .
• Examples:-Keyboard, Mouse, Touch pad, Track Ball etc.

9. Central Processing Unit (CPU)
• Control center or the brain of a computer
• The role is to use a stored program to manipulate the
input data into the information required.
• The CPU consists of electronic circuits that interpret
and execute instructions; it communicates with the
input, output, and storage devices.
• It has two components:-
Arithmetic Logic Unit (ALU)
Control Unit (CU)

11. Arithmetic Logic Unit
• Performs arithmetic and logical operations
• These operations provide the capability of decision-making to the
computer
Control Unit
• Controls and guides the flow and manipulation of data and
information.
• It sends appropriate control signals
• Major function is program execution
– The control unit fetches an instruction and data associated with
it from memory.
– The control unit decodes the instruction.
– The arithmetic/logic unit executes the instruction.
– The arithmetic/logic unit stores the result in memory

12. Output Unit
• Formed by output devices attached to the computer.
• Converts the electronic binary signals into human
readable form.
• Examples:-Monitor, Printer, Plotter etc.

16. Memory
• Memory is the place where raw data, intermediate
data and processed data are stored.
• It can hold data only temporarily because it requires a
continuous flow of electrical current. If current is
interrupted, data is lost.
• Memory is in the form of a semiconductor or silicon
chip and is contained inside the computer.

18. • Two types of memory: ROM and RAM.
• Memory is measured in bytes.
• A byte is usually made up of 8 bits and represents
one character—a letter, digit, or symbol.
• The number of bytes that can be held is a measure of
the memory and storage capacity.

19. Hardware and Software
A computer system consists of hardware and software
for the proper functioning:
–Hardware
The equipment associated with a computer system is the
hardware.
Input devices, CPU, output devices and storage devices form
the h/w
–Software
A set of instructions which govern the operation of the
computer system and make the h/w run.

20. Other types of Computers
• A Notebook computer can fit into a briefcase and weigh fewer
than two pounds,
• A larger, heavier version is called a Laptop computer.
• Smartphone is a small computer

21. Notebook Computers
Laptop Computer

22. 1.22
1-1 TURING MODEL
The idea of a universal computational device was first
described by Alan Turing in 1937. He proposed that all
computation could be performed by a special kind of a
machine, now called a Turing machine. He based the
model on the actions that people perform when involved
in computation. He abstracted these actions into a model
for a computational machine that has really changed the
world.

23. 1.23
Data processors
Before discussing the Turing model, let us define a
computer as a data processor. Using this definition, a
computer acts as a black box that accepts input data,
processes the data, and creates output data (Figure 1.1).
Although this model can define the functionality of a
computer today, it is too general. In this model, a pocket
calculator is also a computer (which it is, in a literal sense).
Figure 1.1 A single purpose computing machine

24. 1.24
Programmable data processors
The Turing model is a better model for a general-purpose
computer. This model adds an extra element to the specific
computing machine: the program. A program is a set of
instructions that tells the computer what to do with data.
Figure 1.2 shows the Turing model.
Figure 1.2 A computer based on the Turing model

25. 1.25 Figure 1.4 The same data, different programs

26. 1.26
The universal Turing machine
A universal Turing machine, a machine that can do any
computation if the appropriate program is provided, was the
first description of a modern computer.
It can be proved that a very powerful computer and a
universal Turing machine can compute the same thing.
We need only provide the data and the program—the
description of how to do the computation—to either
machine.
In fact, a universal Turing machine is capable of computing
anything that is computable.

27. 1.27
1-2 VON NEUMANN MODEL
Computers built on the Turing universal machine store
data in their memory. Around 1944–1945, John von
Neumann proposed that, since program and data are
logically the same, programs should also be stored in
the memory of a computer.

28. 1.28
Computers built on the von Neumann model divide the
computer hardware into four subsystems: memory,
arithmetic logic unit, control unit, and input/output (Figure
1.5).
Four subsystems
Figure 1.5 The von Neumann model

29. 1.29
The von Neumann model states that the program must be
stored in memory. This is totally different from the
architecture of early computers in which only the data was
stored in memory: the programs for their task was
implemented by manipulating a set of switches or by
changing the wiring system.
The memory of modern computers hosts both a
program and its corresponding data. This implies that both
the data and programs should have the same format, because
they are stored in memory. In fact, they are stored as binary
patterns in memory—a sequence of 0s and 1s.
The stored program concept

30. 1.30
1-3 COMPUTER COMPONENTS
We can think of a computer as being made up of three
components: computer hardware, data, and computer
software.
Computer hardware today has four components under the
von Neumann model, although we can have different types
of memory, different types of input/output subsystems, and
so on.
The von Neumann model clearly defines a computer as a
data processing machine that accepts the input data,
processes it, and outputs the result.