Chapter 2
In Brief…
Chapter 2
…Is a little boring. Sorry.
But it contains material you
need to be familiar with
Terms
Bandwidth - how much you can send
through a connection
Bps - bits per second
Kbps - 1000 bps
Mbps - 1000 Kbps
Gbps – 1000 Mbps
Technology
Name
D/L Speed
Cons
Modem
56 Kbps
Very Slow
ISDN
128 Kbps
Expensive
DSL
1.5-8.4 Mbps
Avail., Sym., Dist.
T1 Line
1.5 Mbps
Expensive
Cable Modem
10 Mbps
Saturation, Sym.
T3 Line
45 Mbps
Expensive
http://pirate.shu.edu/~hoffmake/Bandwidth_cht.html
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The rest of CH 2
Is mostly basic, so we’re not going to
cover it in lecture
However, you will be expected to be
familiar with any terms and ideas
introduced in it
Hardware – The System Unit
Representing Information
A Bit: the unit of information in a computer.
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Computers "process" electric currents
(electrical events).
The current is either "on" (=1) or "off" (=0) in a
particular circuit at a particular time.
This gives rise to the binary system for storing
information.
Each transistor in a computer's memory can
hold one bit of information (either a 0 or a 1).
Representing Information
Basic Measures for Information Capacity
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The information capacity of a storage deviced is measured in
multiples of bits.
Bit: 0 or 1.
Byte: 8 bits. Can represent one of 2^8 = 256 numbers.
Kilobyte: Kilo (thousand) + byte: 2^10 bytes = 1,024 bytes.
Megabyte: Mega (million) + byte: 2^20 bytes = roughly a million
bytes.
Gigabyte: Giga (billion) + byte: 2^30 bytes = roughly a billion
bytes.
Terabyte: Tera (trillion) + byte: 2^40 bytes = roughly a trillion
bytes.
Petabyte: Peta (quadrillion) + byte: 2^50 bytes = roughly a
quadrillion bytes = 1,000,000,000,000,000 bytes.
Representing Information
Information
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Information as we think of it is data with meaning: text, pictures,
sounds.
Information as the computer knows it is bit strings: strings of bits
(e.g. "10011101010").
Information as we know it is encoded in a computer using bit
strings.
An encoding is an agreed-upon standard that dictates the
specifics of how the information is represented using 0s and 1s.
Example: ASCII is a widely-used text encoding standard. Under
this encoding, each letter & digit & punctuation mark is assigned
an 8-bit code which represents it. (How many possible such
codes are there?)
Newer (more comprehensive) standard for text encoding:
UNICODE.
Hardware
The rest of the lecture is found at the
following web page:
http://www.cs.indiana.edu/classes/a111/lecture2.html
We’ll be covering this material over the next few
lectures