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Hardware
…and the stupidity of a computer
Hardware and software
• In order to make a computer do something
useful, we need both hardware and software
• Hardware: The physical parts of the computer
(monitor, keyboard, mouse and whatever is
”inside the box”)
• Software: The computer programs (Word,
Messenger, Counterstrike, Internet Explorer,…)
we use for solving various tasks using the
computer
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The computer way
• In order to understand
hardware, you need to
know a little about how a
computer ”thinks”
• A computer does not
”think”, it calculates!
• How can you make pieces
of metal calculate anything
useful…?
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On or Off
• A computer calculates using
metal and current
• A computer can only ”sense”
if a current is ”On” or ”Off”
• How can we employ this for
doing calculations?
• A transistor is used for this
exact purpose
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Transistor
• A transistor is a very simple
electronic device
• Two wires lead into the transistor,
one wire leads out
• The smart part: The transistor can
perform a (sort of) calculation,
based on whether or not there is a
current in the two input wires
• A so-called logical function
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A smart (?) transistor
• So, what calculation is that?
• Not so impressive, actually
Output
Input
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A
B
Y
Off
Off
On
Off
On
On
On
Off
On
On
On
Off
Logical, right…?
• The calculation performed by
the transistor is an example of a
logical function
• A logical funtion takes one or
more input values, and produces a single output value
• BUT these values can only be
either true or false
• Also know as Boolean logic
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Logical functions - example
Two input values
Four possible
combinations
A
false
false
true
true
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B
false
true
false
true
Output
Y
Logical functions - example
Three input values
Eight possible
combinations
A
false
false
true
true
false
false
true
true
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B
false
true
false
true
false
true
false
true
C
false
false
false
false
true
true
true
true
Y
Logical functions - transistor
If we put
Off = false
On = true
A
false
false
true
true
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B
false
true
false
true
Y
true
true
true
false
Zeroes and Ones
• If we now exchange true with 1 (one), and false
with 0 (zero), the previous table becomes:
A
B
Y
0
0
1
0
1
1
1
0
1
1
1
0
• This is how we usually
denote ”On” and ”Off”
• A numeral system using
only 0 and 1 is also
known as a binary
numeral system
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The binary numeral system
• Computers use the binary numeral system
(aka base-2), humans (mostly) use the decimal
numeral system (aka base-10)
• In the context of a base-10 system, 110 means:
1x100 + 1x10 + 0x1 = 110
• In the context of a base-2 system, 110 means:
1x4 + 1x2 + 0x1 = 6
• Alternatively:
– 11010 = 1x102 + 1x101 + 0x100 = 110
– 1102 = 1x22 + 1x21 + 0x20 = 6
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The binary numeral system
• Even if binary numbers appear a bit strange, the
rules for calculation are the same as for base-10
– In base-10:
– In base-2:
5 + 7 = 12
101 + 111 = 1100
• Using a carry works just as before:
0+0=0
0+1=1
1+0=1
1 + 1 = 0, and 1 to carry
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Transistors revisited
• The transistor we saw before
was not able to do correct
binary addition
• However, if you are clever
enough, you can combine
transistors to implement
other logical functions
• Proper binary addition is just
a special logical function
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1+1 = ?
Transistors revisited
• The original transistor worked like this:
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A
B
Y
0
0
1
0
1
1
1
0
1
1
1
0
Transistors revisited
• If you combine two transistors, you can
implement a different logical function
A
B
Y
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A
B
Y
0
0
1
0
1
0
1
0
1
1
1
1
Transistors revisited
• The combination before was not very useful, but
we can of course just build more complex
combinations, involving more transistors
• Our goals is to be able to do binary addition
• Binary addition is ”just” a special logical function,
taking three input values and producing two
output values
• Can be considered to be two separate logical
functions
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Binary addition
A
B
Carry
in
Y
Carry
out
0
0
1
1
0
1
0
1
0
0
0
0
0
1
1
0
0
0
0
1
0
0
1
1
0
1
0
1
1
1
1
1
1
0
0
1
0
1
1
1
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This should do the trick…
• Some clever person found out that the below
combination implements proper binary addition
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The first building block
• We have now found a way
to do proper addition, using
metal and current
• Implementing the other
arithmetic operations is then
not particularly complicated
• This actually forms the
foundation for the first
electronic computers
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ENIAC
•
•
•
•
•
Built around 1945
Weighs about 30 tons
Based on vacuum tubes
Ca. 18.000 transistors
Used for calculating
projectile trajectories
• Was only operational
about half of the time…
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60 years later
• Today we do not use individual transistors. A
chip contains a (large) number of transistors
• Most advanced chips contain a few billion
transistors – within an area of perhaps 1 cm2
• What if car technology had progressed at the
same rate:
– Price: 1 $
– Gas consumption: 10.000 km/l
– Max speed: 100.000 km/h
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Moore’s law
• ”Within two
years, the
number of
transistors on
a chip will
double”
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From 0 and 1 to Counterstrike
• Even if we can now make
metal and current do calculations, there is still a very
long way from 0’s and 1’s to
Counterstrike…
• A computer can handle vast
amounts of data, at vast
speeds
– How fast?
– How much data?
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Bits and bytes
• For a computer, the basic unit for data is
an entity which is either 0 or 1
• This entity is called a bit
• A computer performs operations on bits.
• A more practical unit is a sequence of 8
bits; this is known as a byte.
• Why 8 bits? Why not 7 or 9? Tradition…
• We can for instance define a character set
using 8 bits
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Bits and bytes
•
•
•
•
How many distinct bytes are there?
One byte is 8 bits, each bit is either 0 or 1
Combinations: 2x2x2x2x2x2x2x2 = 256 (28)
Each combination can now be interpreted as a
specific symbol (letter, number, etc), for instance
the letter ”H”
• With 256 combinations, we have enough
combinations for capital letters, small letters,
numbers, etc..
• Example: ASCII codes
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ACSII codes
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Amounts of data
• Amounts of data are usually measured
in bytes (each byte being 8 bits)
• For a computer, all kinds of data are
just sequences of bits
• It requires a program – written by
humans – to interpret a bit sequence
as e.g. music, video, a Word document, and so on
• How many bytes does each type of
data require?
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Size of some data types
Plain text
(no pictures)
Music
(mp3 format)
Video
(DVD quality)
Kilo-byte
Half a page
---
--
Mega-byte
500-page
novel
One minute
One second
Giga-byte
Large bookshelf
16 hours
20 minutes
Tera-byte
Large library
Two years
Two weeks
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Speed of calculation
• When a computer calculates, it
processes many sequences of bits
simultaneously
• All calculation units must be ”syncronized” for this to work properly
• A ”conductor” manages when the
calculation units should calculate
• The speed of the conductor defines
the speed of the computer
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Speed of calculation
• How many ”beats per
second” (hertz) can the
conductor manage?
• Old computer (ENIAC);
about 10.000 beats per
second (10 kiloHertz)
• Modern PC; about
3.000.000.000 beats per
second (3 GigaHertz)
• Also known as clock rate
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3.000.000.000 Hertz
• Three billion beats per second
is quite fast…
• For every beat, light only travels
10 centimeters
• The physical size of the chip
begins to matter
• Unfortunately, energy consumption rises with the clock rate, at
a quadratic rate
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CPU
• Where are calculations actually performed?
• Calculations are done in a unit called the CPU
(Central Processing Unit)
• This unit is basically just one large chip, which
looks fairly uninteresting…
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The CPU and Primary Storage
• The job of the CPU is to perform
calculations on streams of bits,
but who provides these bits?
• Somebody has to feed bits to
the CPU, and ”consume” the
results produced by the CPU
• For this task, the computer uses
the Primary Storage
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Primary Storage
• A calculation involves the below steps
– Input data is moved from primary storage to the CPU
– The CPU performs the calculation
– The result is moved from the CPU to primary storage
• The primary storage is thus just a ”container” for
a certain amount of data
• The primary storage is ”passive”; no kind of data
processing is performed here
• Primary storage is usually of the type RAM
(Random Access Memory)
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Primary Storage
• What is primary storage physically?
• Just some chips, which contains a
certain amount of data
• A modern PC will typically have 2-8
Gigabytes of primary storage
• What could the data represent? For
instance data from an mp3-file, for
which the CPU must perform some
calculation to transform it into music
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Primary vs. Secondary
• Primary storage (RAM) has a large advantage:
transfer of data between the CPU and RAM is
quite fast (several Gigabytes pr. second)
• Fast – but compared to what?
• There are however also several drawbacks:
– RAM is expensive (compared to what?)
– When power is cut, all data in the primary storage will
be lost
• We thus also need secondary storage
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Secondary storage
• Who provides data to the primary storage? That
data is provided by secondary storage
• What is secondary storage? In principle the
same as primary storage – a passive container
for data - but
– Is much cheaper than RAM (per byte)
– Data is preserved when power is turned off
• Presently, the most common form of secondary
storage in a PC is a hard drive
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Quite hard…(old school)
• A (traditional) hard drive contains a number of magnetic
platters, on which individual
bits are stored by magnetising
a specific area of the platter
• A modern hard drive contains
500-2,000 Giga-bytes of data
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Quite hard…(new school)
• A SSD (Solid-State Drive)
hard drive contains a number
of memory chips, on which
individual bits are stored in
transistors (but retained when
power is turned off)
• A modern SSD contains 60500 Giga-bytes of data
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Hard drive vs. RAM
Hard drive
(Traditional)
Hard drive
(SSD)
RAM
Typical amount
in PC
500-2000 GB
60-500 GB
2-8 GB
Price pr.
Gigabyte
≈ 0,5 kr.
≈ 10 kr.
≈ 100 kr.
Data transfer
speed
0,1-0,3 GB/sek
0,5-1 GB/sek
4-8 GB/sek
Preserves data
without power
Yes
Yes
No
Technology
Mechanical
Electronic
Electronic
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Harddisk vs. RAM
• In other words:
• RAM:
– Very fast and stable, BUT
– Expensive, does not preserve data
without power
• Hard drive:
– Cheap, large capacity and preserves data without power, BUT
– Rather slow, mechanical technology
(except SSD)
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Other types of secondary storage
USB-key
CD, DVD
and Blu-ray
Floppy disks Online
Capacity
(Gigabytes)
2-256
0,7-30
0,0015 (!)
??
Price
(kr pr. GB)
Ca. 10
Ca. 1
>100
??
Speed
(MB pr. sek)
10-100
25
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Depends on
connection
Technology
Electronic
Optical /
Mechanical
Magnetic /
Mechanical
Internet
Note
Same tech
as SSD
Stagnant
Almost
extinct
On the rise
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Motherboard
• A PC contains a board, on which the central
components of the PC are mounted – this board
is usually denoted the motherboard
• The motherboard will (at least) contain
–
–
–
–
CPU
RAM (primary storage)
Auxiliary components
Sockets/slots for adding ”other components”
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Other components
• Examples of ”other components” are:
–
–
–
–
Graphics card
Sound card
Network card
TV card
• In some PCs, these components are found
directly on the motherboard, on others they are
found as extra components, inserted into slots
on the motherboard
• Why…?
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Other components
• Even though a modern CPU is
very fast, it may benefit from being
relieved from certain tasks
• Graphics card
– Specially designed for effective
graphics calculations
– Takes computational load off CPU
– May increase graphical performance
by a factor 100
– Typical application: GAMES!
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Data exchange by bus
• All these units and components
need to exchange data in order
to do their job
• How do they do that?
• Data exchange is done using
so-called data buses
• A data bus transports data
between two units
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Data exchange by bus
• A data bus sends data:
– A number of times pr. second
– A certain amount of data each time
• Example: a 32-bit bus running at 100 Mhz
– Carries 32 bit (4 bytes) each time
– Sends 100 million times pr. second
• A PC contains a number of buses running at
different speeds
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Countryside bus
• A bus is also used for exchanging data with
additional components, like a graphics card
• Types of buses for extra components:
– PCI (Peripheral Component Interconnect) – those
slots in which additional components (such as a
graphics card) can be inserted
– USB (Universal Serial Bus) – used by many external
devices such as printers, USB memory keys, etc..
• Fortunately, buses follow a standard
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External devices
• Devices which enable communication
between humans and computers
• Typical external devices
– Keyboard and mouse
– Monitor
– Speakers / headset
– Printer
• But also
– Digital camera, phone, USB-key, …
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