Five on Forensics Page 1 - Craig Ball

<strong>Five</strong> on Forensics
© 2002-2008 Craig Ball All Rights Reserved
and lower case, as well as punctuation marks and special characters. This set of numbers is
known as the ASCII code (for American Standard Code for Information Interchange,
pronounced “ask-key”), and is commonly used by many different types of computers. By limiting
the ASCII character set to less than 256 variations, each letter (or punctuation mark) can be
stored as one byte of information in the computer's memory. A byte can also hold a string of
bits to express other information, such as the description of a visual image, like the pixels or
colors in a photograph. The byte, then, is the basic unit of computer data.
Why is an eight-bit string the fundamental building block of computing? It just sort of happened
that way. In this time of cheap memory, expansive storage and lightning-fast processors, it’s
easy to forget how very scarce and costly all these resources were at the dawn of the computing
era. Eight bits was basically the smallest block of data that would suffice to represent the
minimum complement of alphabetic characters, decimal digits, punctuation and special
instructions desired by the pioneers in computer engineering. It was in another sense about all
the data early processors could chew on at a time, perhaps explaining the name “byte” coined
by IBM.
Storing alphanumeric data one character to a byte works in places that employ a twenty-six
letter alphabet, but what about countries like China, Japan or Korea where the “alphabet”
consists of thousands of characters? To address this, many applications dedicate two bytes to
recording each character, with the most widely accepted double-byte character system called
Unicode.
Now it may seem that you’ve asked for the time and been told the history of clock making, but
computer forensics is all about recorded data, and all computer data exists as bits and bytes.
What’s more, you can’t tear open a computer’s hard drive and find tiny strings of ones and zeros
written on the disk, let alone words and pictures. The billions of bits and bytes on the hard drive
exist only as faint vestiges of magnetism, microscopic in size and entirely invisible. It’s down
here--way, way down where a dust mote is the size of Everest and a human hair looks like a
giant sequoia--where all the fun begins.
Information Storage
We store information by translating it into a physical manifestation: cave drawings, Gutenberg
bibles, musical notes, Braille dots or undulating grooves in a phonograph record. Because
binary data is no more than a long, long sequence of ones and zeros, it can be recorded by any
number of alternate physical phenomena. You could build a computer that stored data as a row
of beads (the abacus), holes punched in paper (a piano roll), black and white vertical lines (bar
codes) or bottles of beer on the wall (still waiting for this one!).
But if we build our computer to store data using bottles of beer on the wall, we’d better be plenty
thirsty because we will need something like 99,999,999 bottles of beer to get up and running.
And we will need a whole lot of time to set those bottles up, count them and replace them as
data changes. Oh, and we will need something like the Great Wall of China to set them on.
Needless to say, despite the impressive efforts ongoing at major universities and bowling alleys
to assemble the raw materials, our beer bottle data storage system isn’t very practical. Instead,
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