Transcript Fundamentals

Fundamentals
Main Hardware Components
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Central Processing Unit (CPU)
Main Memory (random access memory
or RAM)
Auxiliary Storage
Input Devices
Output Devices
CPU
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Performs arithmetic and comparisons
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The real “brain” of the computer
RAM
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Temporarily stores any program being
executed on the computer, as well as
the data on which the program operates
Auxiliary Storage
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Provides a place where data can be
permanently stored and then
transferred to and from main memory.
Examples: floppy disk, hard disk, CDROM, Zip drives, tape backup
Input Devices
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Accept data from an external source
and convert it to electrical signals,
which are sent to the CPU.
Examples: keyboard, mouse, joystick,
scanner, microphone
Technically, auxiliary storage is also
considered an input device
Output Devices
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Accept electrical signals from the CPU
and convert them to a form suitable for
output.
Examples: monitor, printer, speakers
Technically, auxiliary storage is also
considered an output device.
Bits and Bytes: How Data is
Represented in the Computer
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All computer calculations are done using
binary arithmetic, which uses only 0’s and
1’s. Each binary digit (0 or 1) is called a bit.
This is convenient for the computer hardware
because in any circuit, 0 might be
represented by a low voltage signal and 1
might be represented by a higher voltage
signal. I.e., it’s easy for the electronics to
distinguish between just two possible values.
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But much of the data we use on the
computer isn’t really numerical.
How does the computer represent
things like alphabetic data, or pictures,
for example?
Answer: It still uses bits.
Bytes
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Computer storage is arranged into bytes,
where each byte is just a group of 8 bits.
A byte is considered the smallest
addressable unit of memory, and
measurements of memory size or disk
capacity are always expressed in terms of
bytes.
Bytes are also convenient for representing
alphabetic data.
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An 8-bit byte can contain any of 28 = 256
different combinations of 0’s and 1’s, like
00000000, or 01101001, or 11111111, for
example.
Alphabetic characters are represented in
the computer, one byte per character,
using ASCII codes.
ASCII Codes
A
B
C
D
Etc.
01000001
01000010
01000011
01000100
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The codes for the lower-case letters are
different, and there are distinct codes
for all the other standard characters
appearing on the keyboard, including
punctuation marks, the space, the
carriage return, and the 10 digits. But
each of these fits into a single byte.
Everything is stored as bytes
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Other kinds of data are also ultimately
stored as bytes, using some kind of
coded representation.
For example, a single digital image can
be represented by specifying what
appears (color, intensity, etc.) in each
separate pixel (picture element) of the
image.
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Because there are potentially a very
large number of pixels in a high-quality
image, it may take many bytes to
represent this image.
And, of course, if this is a changing
video image, the number of bytes to
represent it will be much larger still.
Data Compression
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One thing that helps reduce the
number of bytes required is the use
of data compression.
An example of a data compression
program is WinZip.
Another type of data compression is
used in .jpg images.
How does data compression
work?
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To give a simple-minded example, suppose that
we wanted to store (or transmit) a sequence of
100 bytes, all of which were identical (say ASCII
for the character A).
Instead of using 100 bytes for this, we could use
2 bytes, one representing the number 100
(which is 01100100 in binary) and the other
representing the ASCII code for A.
Thus in this case we’ve compressed 100 bytes
down to 2.
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The general idea behind data
compression is to be able to find
patterns in the original data which can
be encoded in a shorter way.
Uncompressing the data then just
requires regenerating the original data
from this shorter pattern description.
Programs are in bytes too
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Also represented as bytes in the
computer are the instructions that
make up the executable programs that
the CPU runs.
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Thus everything in the computer, programs
or data, is ultimately just bytes (or bits), as
far as the internal workings go at the lowest
levels of the electronics.
Fortunately for us, though, as computer
users, or even as computer programmers,
we don’t have to interact with the computer
at this level.
CPU
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The standard personal computer (PC)
has a single-chip CPU, also called a
microprocessor.
Examples of microprocessors found in
standard PCs are Intel’s Pentium,
Pentium II, Pentium III, and Celeron.
Other manufacturers making Intelcompatible microprocessors are AMD
and Cyrix.
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Microprocessor speed is typically
expressed in terms of the number of
“clock cycles” per second, a rough
measure of the number of program
instructions that can be carried out in
each second.
One clock cycle per second would be 1
hertz (Hz).
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Actual speeds of current top-end PC
microprocessors range from roughly
250-500 megahertz (MHz), which
means 250 million to 500 million clock
cycles per second.
The higher this number, the faster the
processor.
Standard Prefixes Used to
Express Various ComputerRelated Quantities
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Kilo means 103 or 1,000
Mega means 106 or 1,000,000
Giga means 109 or 1,000,000,000
Tera means 1012 or 1,000,000,000,000
Milli means 10-3 or 0.001
Micro means 10-6 or 0.000001
Nano means 10-9 or 0.000000001
Main Memory (RAM)
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Called random access because any
particular memory location in it is as
fast to retrieve data from or store data
in as any other.
Furthermore the time it takes is very
short, less than 1 millisecond, so
accessing data in main memory is very
fast.
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But the data stored in it only lasts as long
as there is power being supplied to the
computer.
Typical PCs have 32 or 64 megabytes
(MB) of RAM. The more RAM, the faster
the computer will seem to run because
there is less time spent storing or
retrieving the data on disk, which is
much slower.
Hard Disk
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Stores data on spinning magnetic
platters in a sealed enclosure.
Typical capacity of a hard disk on a PC
is 1 or more gigabytes (GB).
Typical access time for a hard disk is on
the order of 10 milliseconds, on
average, which is much slower than the
access time for main memory.
Floppy Disk
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Made of flexible plastic coated with
magnetic material, and enclosed in a
hard plastic case.
Its capacity is 1.44 MB, and its average
access time is around 175 milliseconds.
Other Auxiliary Storage
Devices
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CD-ROM (Compact Disk, Read-Only
Memory)
DVD (Digital Versatile Disk, or originally
Digital Video Disk)
Zip Drive
Tape Backup Unit
Input Devices
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Keyboard
Mouse
Microphone
Scanner
Digital Camera
Joystick
Output Devices
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Monitor
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Printer
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CRT (cathode ray tube)
LCD (liquid crystal display)
Inkjet
Laser
Speaker
Software
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System Software (Operating System)
Application Software
System Software
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Main function is to maintain the file
system and also to allow application
programs to have access to computer
input (from the keyboard or mouse, for
example) and to create computer output
(to the monitor, for example).
Provides an interface between application
programs and the hardware itself.
Files and Folders
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A file is a collection of bytes on the disk
that represents a program or data for
use by a program.
Files are organized hierarchically, in a
tree structure. Files that contain other
files are called folders in Windows
95/98 and directories in older operating
systems like DOS and Unix.
Application Programs
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Application programs represent all other
software that can be run on the
computer, to allow the user to do such
varied tasks as word processing, playing
games, sending email, and browsing
the World Wide Web, for example.
These programs are typically obtained
from vendors but application programs
can also be created by sophisticated
users.
Specific application programs we will use
in this course are:
 Internet Explorer (for web browsing)
 Word (for word processing)
 Excel (for spreadsheet manipulation)
 Access (for database manipulation)
 PowerPoint (for creating and showing
presentations)