Transcript Computer Systems - Douglas Academy

What is a Computer?
A computer is an information processing
machine.
A computer only follows the instructions it is
given.
Data is Input, Processed and then Output.
I’m ONLY a
machine!
Two types of data - Analogue and
Digital
Analogue data can be of a wide range of
values.
Examples are: Temperature, Noise Level,
Speed.
Digital information is stored in blocks.
Examples are On/Off; Population
Data and Information
Data has no meaning
Data is made up of symbols e.g.
871652; H789 IOS; £76.91
Information has a meaning
We understand what a piece of information is
about e.g
Telephone Number: 871652
Car License Plate: H789 IOS
IPO - Input, Process, Output
INPUT
PROCESS
OUTPUT
Data is INPUT into the computer
system
It is then PROCESSED to produce
useful Information as OUTPUT.
Standalone Computer System
A system is a collection of parts that work together.
A standalone computer system is a computer system
that is NOT connected to other computers.
It consists of at least one input device, a processor
and one output device.
The Central Processing unit contains the processor
and main memory.
Programs and data are stored in main memory
Types of Media
Media is the material used in devices.
Examples of media are Floppy disc and CDROM.
If CD-ROM is the MEDIA then the CD-ROM
drive is the DEVICE.
Devices
Devices are either INPUT, OUTPUT or
BACKING STORAGE.
Input devices allow us to enter data into the
computer system (mouse, microphone etc).
Output devices allow us to receive
information from the computer system
(monitor, speakers, robot).
Backing storage devices allow us to store
programs and data so that we can use them
later (floppy disc drive, magnetic tape drive ,
CD-ROM drive).
Hardware and Software
Hardware refers to all the parts of the
Computer System that we can touch.
Examples of hardware are monitors, joysticks,
printers.
Software refers to all the programs and data
that we use with the computer.
Input Devices
Mouse
A device which allows a computer user to move
the screen cursor or pointer. A mouse usually
has one or more buttons on top, a ball on the
bottom and a cable connecting the mouse to
the computer. Movement of the mouse causes a
relative change in cursor location. Clicking the
button causes a screen item or command to be
selected.
Keyboard
Similar to a typewriter, contains the letters for
typing text, and keys that give the computer its
commands.
Touch Sensitive Screen
A Touch Sensitive Screen is a pointing device
that enables the user to interact with the
computer by touching the screen.
Input Devices
Trackball
A trackball is basically an upside down
mouse. A trackball allows the user to move a
small ball in order to move the pointer across
the screen.
Trackpad
A trackpad mouse is a touch sensitive
surface. The user places a finger on the
surface and when the finger moves across
the surface the mouse also moves.
Trackpads are more commonly referred to as
Glidepoint mice.
Input Devices
Graphics Tablet
A graphics tablet allows the user to draw
on a special worktop. As the user draws
the details are stored on the computer
system. These devices are most often
used by architects and designers.
Joystick
Joystick is a term used for the handhold
tool used in many computer-based video
games. The joystick is designed after the
steering stick of military airplanes,
allowing movement in all four directions
as well as rotational movement. In
addition, buttons with certain functions
can be located at several positions on the
joystick.
Output Devices
VDU
Visual Display Unit (VDU) is the proper
name for the computer monitor. The
VDU allows us to see the output from
the computer.
Plotter
A plotter is a device used for creating
a hard copy of the output from a
computer system. Plotters use special
pens to draw the output as a series of
lines. Plotters are often used to
output building drawings and designs.
Output Devices
Printers
Laser Printer
• A type of printer that
uses a laser beam to
produce an image on
a drum and then ink
dust (toner) sticks to
the image. This dust
is pressed onto
paper and then
heated to make it
stick.
The resolution of printers and other output devices can
be measured in dots-per-inch (dpi).
Output Devices
Printers
Inkjet Printer
• A printer mechanism that sprays one
or more colours of ink onto paper and
produces high-quality printing. A
typical black ink cartridge contains a
print head with up to 144 nozzles.
Each nozzle is responsible for a single
dot of ink.
An inkjet cartridge
Output devices
Comparison of Laser with Inkjet
Laser printer
Expensive to buy
High quality output
Very quick to print a
page
Relatively low cost of
toner
Prints quietly
Colour models expensive
and most costly to run
Inkjet printer
Cheap to buy
Good quality output (but
not as good as laser)
Slow to print a page
Relatively high cost of
new ink cartridges
Quiet, but noisier than
laser
Relatively cheap colour
printing when compared
to laser colour printing.
Backing Storage Devices
Magnetic Tape
A data storage medium used for backup. The tape
is made of a thin plastic strip with a magnetic
oxide coating on one side. To read or write, the
tape drive winds the tape from one reel to
another, causing it to move past a read/write
head.
Backing Storage Devices
Floppy disk
The floppy disc was the main type of data storage
used for many years but has been replaced by
larger capacity USB Sticks and other removal media
(such as Zip disc and flash cards). A floppy disc
can store 1.44 Mb of data – the smallest USB Sticks
hold approximately 32Mb.
Hard disc
A high capacity storage device inside your PC.
Often known as drive C: although many computers
may also have a drive D:. The hard drive disks are
most often made from machined aluminium and
have a similar magnetic coating painted on them
that the floppy disk has.
Using disks and making backups
Disc Label
Write Protect Tab
A floppy disc is used to save data.
It can be used to make a backup copy of
small files.
A backup is a second copy of your data that
you take in case something happens to the
original.
The original might get Lost
Corrupted (i.e. made unreadable)
Damaged
Stolen
You should always make a backup of
important files.
And don’t keep the backup in the same
place as the original copy!
Format and Copy Discs
New discs must be formatted for the type of
Computer System that they will be used in.
Files can be copied to floppy disc to create backup
copies.
To format a floppy disc in Windows.
Double click the ‘My Computer’ Icon.
Insert the floppy disc to be formatted.
Right click ‘3½ Floppy [A]’ Icon
Left click ‘Format..’
Click ‘Full’ to carry out a full format of the Disc (‘Quick’ just
erases an already formatted disc)
Click ‘Start’ to format your disc. A message will be displayed
when the format is finished.
Copying to a Disc (Windows)
Locate the files you want to copy.
Select the files to be copied
Left click Edit in the Window menu toolbar.
Left click ‘Copy’
Double click the 3½” Floppy [A] icon.
Left click Edit in Window menu toolbar.
Left click Paste. The files will be copied to
the floppy disc.
Backing Storage Devices
CD-ROM
A standard medium for storage of digital data, read
with a laser-based reader. CDs are 12cms in
diameter. CD-ROMs are manufactured with data on
them – the data is pressed into the plastic using a
special digital mould. CD-ROMs are never written
onto (they are different from CD-R and CD-RW
formats). Capacity 650 Mb or 74mins of music.
DVD-ROM
Digital Versatile Disc Read Only Memory. Similar to
a CD-ROM, it uses DVD technology to pack up to 25
times the information found on a CD-ROM. DVDROM drives can also play DVD movies and other
high quality multimedia. Capacity: up to 8.5 Gb
Computer Networks
A network is made up of two or more
computers linked together.
Advantages are:
•
•
•
•
Share devices between computers
Share data between computers
Share programs between computers
Saves time
A typical Local Area Network
A local area network is a computer network across one building
or site.
Printer
Work Station
Fileserver
Network Cable
Types of Computers
Microprocessor
Smallest
– A small chip programmed with instructions.
Palmtop
– A computer small enough to fit in the user's hand.
Primarily used as personal organisers.
Laptop
– A small, portable computer -- small enough that it can
sit on your lap. A laptop computer can be called a
notebook computer.
Desktop
– A desktop computer is personal computer that can fit
on an end user's desk and perform business
computing tasks. Also, especially if linked to a network
of other computers, it may be referred to as a
workstation.
Biggest
Bits and Bytes
The computer is a digital machine.
All data in the computer is stored digitally.
Digital data in the computer is stored as zeros and
one (called binary) e.g.
Binary
0
1
10
11
100
101
110
111
1000
Decimal
0
1
2
3
4
5
6
7
8
More Bits and Bytes
Each 1 or 0 is called a BIT (short for Binary Digit).
Eight bits are called a BYTE.
1024 (roughly 1000) bytes is a KILOBYTE (Kb for short)
1024 kilobytes is a MEGABYTE (Mb for short)
1024 megabytes is a GIGABYTE (Gb for short)
1024 gigabytes is a Terrabyte (Tb for short)
These units are used to measure the
size of storage (called CAPACITY) or
storage requirements e.g. the available
memory, hard disk space, program size.
Computer System - Block Diagram
The Computer System consists of four parts.
Input, Processor, Output, Backing Storage
Input
Data Flow
Processor
Backing
Storage
Output
What is the CPU
CPU - Central Processing Unit
It is the combination of the Processor and
Memory.
There are TWO types of memory in the CPU,
RAM and ROM.
Central Processing Unit
RAM
ROM
PROCESSOR
Data Flow
RAM and ROM
RAM is Random Access Memory
It can be written to and read from. It is where most
programs and data are stored while the computer is
being used.
ROM is Read Only Memory
Data stored in ROM can only be read, it can never be
written over or deleted. We normally store important
programs in ROM to do with the computers Operating
System (see later).
Storing Numbers
Numbers are stored in binary.
1Bin
is
1Dec
10Bin
is
2Dec
1000Bin
is
8Dec
1001Bin
is
9Dec
1111Bin
is
15Dec
11111111Bin
is
255Dec
You don’t need to understand binary (that’s Maths)
but you do need to know that it is how most numbers
are stored in the computer.
Storing Graphics
Black and White graphics as stored using pixels
(Picture Elements).
The image to be stored is broken up into dots, each
dot is a pixel.
The pixels are ON for black and OFF for white e.g.
1
1
1
0
0
0
0
0
0
0
0
0
0
1
1
1
0
1
1
0
0
0
1
1
0
0
0
0
1
0
1
1
0
0
0
0
1
0
1
1
0
1
1
0
0
0
1
1
0
0
0
0
0
1
1
1
1
1
1
0
0
0
0
0
Storing Text
Text is stored using a special set of codes
called ASCII.
Each symbol (letter, number etc) has its own
unique code e.g.
a is 97, A is 65, ? is 63, 3 is 51
ASCII (American Standard Code for
Information Interchange)
One ASCII code is one byte long (eight bits).
Capacity
The size of memory, hard disc space, floppy drive
space, programs, data files etc. are all measured by
the number of bytes, kilobytes, megabytes or
gigabytes (1024 megabytes) they can store.
=
445 floppy discs
1 CD-ROM
More on Memory
Computers store blocks of data called ‘words’
in memory (A 32 bit computer has words
that are 32 bits long).
Each place that can store a word is called a
storage location.
Each storage location has a unique address
that identifies it from all the other locations.
Types of Computer
Mainframe Computer
A very large computer capable of supporting
hundreds/thousands of users running a variety of
different programs at the same time.
Typically used by large businesses and for
scientific purposes.
What is software
Software
is the term that we use for all the programs and
data that we use with a computer system.
Two types of software
Program - the instructions that the computer
follows (e.g. a word processor or a game).
Data - what the programs process (e.g. a word
processing document or a saved game file)
Machine Code
Computers only understand binary codes.
This means that ALL the programs that a
computer carries out must also be in binary
code.
The binary language that a computer
processor can understand is called MACHINE
CODE
Machine code is DIFFERENT for each type of
processor – Apple Mac computers use a
different processor and therefore a different
machine code from PCs.
Low Level Languages
Computers only understand binary!!!
All programs have to end up in binary
language in order work.
The binary language that the computer
understands is called MACHINE CODE
Machine code looks like this…
00100111,01110100,10010001
NOT very easy to understand.
That’s why High Level Languages have been
produced...
High Level Languages
We use high level languages (HLLs) because
programming in machine code is VERY
difficult.
High level languages make it easier for us to
write programs because we can use
commands that mean something (PRINT,
END, IF, THEN).
High level language programs still have to be
translated into machine code to work. This
is done by a translator.
There are lots of different HLLs but they all
still have several things in common...
Common features of High Level
Languages
English like words and phrases as instructions eg.
PRINT, IF, THEN, END, STOP, ELSE, OPEN etc.
Arithmetic operations such as multiply, divide, add
subtract etc.
High level languages are problem
orientated. This means that the
programmer can forget about the
internal workings and set-up of the
computer system and can
concentrate on solving the problem.
Common features of High Level
Languages
Words and symbols are combined to conform
to a predefined SYNTAX to produce program
instructions (also called statements). Syntax
are the rules which govern how the program
commands are used (similar to the rules of
grammar that govern how we use the English
language).
Must be translated into machine code. A
special program (a type of systems software)
called a translator does this….
Types of High Level Language
General purpose
General purpose high level languages are written for
a wide variety of tasks. They can be used for any
type of application however they may lack certain
commands that make particular tasks easy to do.
Special Purpose
Special purpose high level languages are written for
particular types of task. For example Delphi is
written for windows database programming and has
special commands that make this type of task easier
to carry out.
OS - Different modes of processing
There are several different modes of processing.
Interactive
Accepting input from a human. Interactive computer systems are
programs that allow users to enter data or commands. Most popular
programs, such as word processors and spreadsheet applications, are
interactive. In interactive processing, the application responds to
commands as quickly as it can once they have been entered.
Sometimes there is a delay while the processor finishes another task.
Real Time
Real-time operating systems are systems that respond to input
immediately. Automatic teller machines for banks are an example of
real time processing. Real time systems are used for tasks such as
navigation, in which the computer must react to a steady flow of new
information without interruption.
More Input Devices
Scanner
A scanner is used to take information
stored on paper and read it into a
computer system. Scanners can be used
to convert photographs, paintings etc. or
even typed text into a form that can be
stored on a computer.
Digital Still Camera
A digital still camera looks and behaves
like a regular photographic camera,
except instead of using film, it stores the
image it sees in memory as a file for later
transfer to a computer. Many digital
cameras offer additional storage besides
their own internal memory; most use
some sort of memory stick or card.
More Input Devices
Digital Video Camera
A digital video camera takes stores
video on digital tape, disc or
memory card. The video is stored
in a digital format.
The video can then be easily
transferred to a computer for
editing.
Webcam
a digital camera designed to take
digital photographs and/or video
and transmit them over the
internet