This document provides an overview of the history and components of computers. It discusses the evolution of computer hardware from early mechanical devices like the abacus and Babbage's Difference Engine to modern integrated circuits and microprocessors. It describes the key components of modern computer systems including the CPU, memory, storage, buses, and input/output devices. It also explains the functioning of the CPU and memory in more detail.

1. SIMS-201
History Of Computing
Computer Hardware

2. 2
(not from book)
 Computer Development
 Computer architecture
Overview

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Introduction
 Computer is arguably the most important tool in the
areas of engineering, science, business etc. etc.
 Data acquisition and analysis
 Simulation
 Embedded applications

Process control

Condition monitoring and fault diagnosis systems

Automatic testing equipment

Robotics

Telecommunications
 Productivity software (word processing, spreadsheets,
databases, presentation) etc……………

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Computer development
 The Abacus- Babylonia-4th
century B.C.
 The Difference Engine- Charles Babbage 1822
 Vacuum tube - John Ambrose Fleming 1904
 The ENIAC (Electronic Numerical Integrator and Computer)-1945
 Used 17,478 vacuum tubes
 Too late for WW-II, but was used in the cold war to perform
calculations to build a hydrogen bomb

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 City of Philadelphia reportedly experienced brown-outs when
ENIAC drew power at its home at the the University of
Pennsylvania
(http://www.pbs.org/wgbh/aso/databank/entries/dt45en.html)
 Was not a general purpose computer: programming meant rewiring
with punch cards and switches
 One of ENIAC's greatest feats was in showing the potential of what
could be accomplished in the future
 Transistor - Nobel prize in physics in 1956

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 Integrated Circuit (chip) - Jack
Kilby 1958 (Nobel prize in physics in 2000)
 First commercially available IC’s developed
by Texas Instruments and Fairchild
semiconductor corp.
 Generations of IC’s:
 Small scale integration - 1965

Up to 100 devices on a chip
 Medium scale integration - to 1971

100-3,000 devices on a chip
 Large scale integration - 1971-1977

3,000 - 100,000 devices on a chip
 Very large scale integration - 1978 to date

100,000 - 100,000,000 devices on a chip
 Ultra large scale integration

Over 100,000,000 devices on a chip
Apple I computer (1976)

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Moore’s Law: Number of transistors on a
chip will double every 18 months.

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Computer Architecture
Main
Memory
Input
Output
Systems
Interconnection
Central
Processing
Unit

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Components of a Computer System
central processing unit
Storage
(External memory)
input/output Main Memory
(RAM)

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Computer Components

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Component description
 Central Processing Unit (CPU) or
microprocessor, controls the operation of the
computer and performs its data processing functions
 Main memory - also called internal memory stores
instructions and data. Memory is partitioned into
separate instruction and data spaces
 Input/output (I/O) – moves data between the
computer and its external environment
 System interconnection – some mechanism that
provides for communications among the CPU, the
main memory, and the I/O devices

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Structure of the CPU
control unit
registers
flags
cache
memory
ALUinput/output
storage
memory
registers

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Components of the CPU
 Arithmetic and Logic Unit (ALU): processes the data
in the registers according to instructions issued by the
control unit. Performs arithmetic (addition, subtraction,
etc..) and logical (comparison) operations
 Registers: provides temporary storage for data and
instructions. It handles instructions and data at 10 times
the speed of cache memory. Registers facilitate the
movement of data and instructions between RAM, the
control unit and the ALU
 Control unit registers:

The instruction register contains the current instruction being
executed

The program register (instruction pointer) contains the RAM
address of the next instruction to be executed
 ALU registers

The accumulator register stores the result of ALU operations

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 Internal CPU interconnection: some mechanism that
provides for communication among the control unit, ALU, and
registers
 Control Unit: controls the operation of the CPU and hence
the computer. Interprets instructions, moves data to/from
memory and registers, instructs ALU to perform certain
operations, increments instruction pointer, etc. During program
execution, instructions in a program are moved from the RAM
into the control unit, where it is decoded and interpreted by the
decoder
 Flags: 1-bit memory, or 1-bit registers and hold information on
what has recently happened in the CPU. These are set to 1 or
0 depending on the results of internal operations such as results
of ALU operations (zero or negative result) or external
operations such as interrupts (commands that tell the processor
to stop execution and wait for further instruction)

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 Cache Memory: Small fast memory that improves CPU’s
efficiency. Increases computer throughput, and is a high-speed
holding area for program instructions and data. It holds only
instructions and data that are likely to be needed by the CPU.
While programs are running on the computer, the same data or
instructions might be needed frequently. In such cases, the
processor first checks the cache memory for the data or
instructions, thereby reducing the need for frequent access to
the RAM and speeding up the processing

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Microprocessor System Buses
Microprocessor
(CPU)
RAM ROM
Input/Output
(I/O)
Control Bus
Data Bus
Address Bus

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System Buses
 A BUS is an internal communications path consisting of a
number of lines connecting the system components
 Control bus –The control bus synchronizes system events like
memory access, system interrupts, I/O, etc.
 Address bus – Source and destination addresses are sent
over the address bus to identify a particular location in memory
or input/output port.
 Data bus – two way path for transferring data and instructions
in and out of the microprocessor

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Main Memory
 A collection of cells
 Each cell has an address and a value
 Random Access Memory (RAM)
Cells can be accessed randomly
 Ram is volatile
 All data stored in binary format
 Bit, byte and word are the unit of data

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Main Memory
 RAM – Random Access Memory. Temporary read/write
memory. Applications are typically loaded into RAM during
computer use. Types of RAM include:
 SRAM (static) , DRAM (dynamic ), EDO RAM (extended
data out) , SDRAM (synchronous dynamic-most new PC’s
are equipped with this RAM which is able to synchronize
itself with the processor, enabling data transfer at more than
twice the speed of previous RAM technologies)

SRAM is called static because the memory retains its contents as long
as power is supplied-It does not have to be periodically refreshed as in
DRAM. It is faster than DRAM (The contents of the memory can be
read much faster), however is more expensive and is larger in size

DRAM is called Dynamic RAM because the memory content needs to
be refreshed periodically (every few milliseconds) due to leakage of
electrical charge. It is slower than SRAM, but cheaper and smaller in
size

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CPU-Memory Interaction
0 LDA 14
1 ADD 15
2 STA 14
3 HLT
…. ……
14 10
15 7
14 17
15 7
Assume a is stored in 14
and b is stored in 15
a= a + b
Result
Program
Fetch-execute cycle

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 ROM – Read Only Memory. ROM can typically be
written once, but read many times. It is used to store
BIOS (Basic Input/Output System-helps to load and
locate an operating system), external to
microprocessor, and computer instruction sets,
internal to microprocessor
 The contents of the ROM are hard wired by the
manufacturer in a typical ROM chip. When you turn the
computer on, ROM automatically prepares the computer
system and loads the initial display screen prompt
 A variation of ROM is PROM (Programmable Read Only
Memory), in which the user can load programs and data that
are read only. This can be done with device called a PROM
programmer. Writing to a PROM destroys the internal links,
so a basic PROM can only be programmed once

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 EPROMs (Erasable Programmable Read Only Memory) is a
variation of PROM, and is rewritable. It can be erased by
exposing the chip to ultraviolet light. It can then be
programmed with an EPROM programmer
 Flash memory is a type of PROM that can be easily altered
by the user. They are also called EEPROMs (Electrically
Erasable Read Only Memory) because they can be
electrically erased then written on to (flashed) without having
to take them out of the computer, and without using
ultraviolet light.
 Since RAM can be read faster than most ROMs, the
frequently used content of the ROM is sometimes copied to
RAM (shadowed)

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Secondary Storage
 Magnetic disk
 Hard disk (File, Directory, Folder)
 Floppy disks
 Zip disks
 Optical media
 CD (680 MB)
 DVD (4.7 GB)
 Magneto-optical disks (Pinnacle drives)
 Magnetic tape (used primarily for long term
archive)

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Hard Disk Drive Basics

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Input/Output
Some Input Devices
 Keyboard
 Keypad
 Mouse
 Voice activation
 Touch screen
 Digitizers and pen-based (stylus) systems

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Some Output Devices
 Monitor
 Printer
 Speakers
 Communication (comm) ports
 Modems (both input and output)
 Network interface cards (both input and
output)