Hi ho Silver. Who killed the Pony Express? (Software tips and advice)

Name: tagheur

Hello doyoo user, You have to be logged in to use these functions... Login or register Close window

Send message to member

Product:	Software tips and advice
Date:	04/05/02 (217 review reads)
Rating:

Advantages: Now you know what a bit is

Disadvantages: Now you know what a bit is

Eye halve a spelling chequer
It came with my pea sea
It plainly marques four my revue
Miss steaks eye kin knot sea

Eye strike a key and type a word
And weight four it two say
Weather eye am wrong oar write
It shows me strait a weigh

As soon as a mist ache is maid
It nose bee fore two long
And eye can put the error rite
Its rare lea ever wrong

Eye have run this poem threw it
I am shore your pleased two no
Its letter perfect awl the weigh
My chequer tolled me sew

Anon


Computers are capable of three basic functions. They can perform arithmetic, they can compare one value with another which, given a rewriteable medium, implies that they can order, or sort, and they can perform these functions repeatedly according to some stored, or prearranged sequence, or program. This would suggest that they are nothing more than glorified adding machines, however as we are all aware, it is their ability to process and present data in the form of text, audio and graphics which makes them so indispensable to us in our everyday lives. Nevertheless, inside the computer itself there exists a strange world where everything is expressed as a number or a series of numbers. Indeed, this is
why they are known as digital computers. By now you will be painfully aware that
computers use the "binary system" to handle numbers but may be less clear as to how they handle images, text, music video and so on. Just what is the binary system anyway? In
order to find out we have to see what killed the Pony Express..

The Pony Express was perhaps one of the more over hyped events in the history of the old
West. In truth, it only operated for 18 months; from April 1860 to November 1861. The intrepid riders carried mail between St. Joseph, Missouri and San Francisco, California, a distance of some 2000 miles. They must have been real men, with very sore bottoms. It was f
orced out of business, with huge subsequent losses to its backers, by the introduction of the Telegraph.

The American Telegraph, conceived by Samuel Finley Breeze Morse, began the communication revolution. He first demonstrated his system in 1844 with a link that ran between Baltimore and Washington. Morse did not actually invent the telegraph - we
Brits had a system running on the railways as early as 1837, however it was a much more
complicated affair than Morse's using 5 wires to move a pointer mechanism, a bit like a ship's telegraph ("Full speed ahead Mr Bo'son", and all that tosh). The brilliance of Morse' system lay in its simplicity.

Guess what,. - the Telegraph is a binary device! It can only send two signals - a dot or a dash. In 1838 Morse invented a "code" to represent the letters being sent down the line. Everyone knows the classic "dit dit dit, dah dah dah, dit dit dit" code for "SOS". Or you may have heard that bloody annoying Nokia ring tone which goes dit dit dit, dah dah, dit
dit dit - its actually spelling "SMS" in Morse (who says the Scands have no sense of
humour? Lars and Erik must have pissed themselves over that one).

Morse code is clever in that the more frequently occurring characters (in the English language) are given the shortest codes, thus making transmission faster. It is also the oldest example of a Binary Interchange Code, or in plain-speak, a series of two-valued or "binary" sequences to represent numbers and letters.

In 1874, a Frenchman named Jean-Maurice-Émile Baudot patented the first teleprinter. It used a 5-bit code, known as the Baudot Code to represent the characters that it sent and received down the telegraph (and later telephone) line. By "5-bit", we mean that each character is represented by a sequence of 5 binary values. For example, the letter "A" is represented
by the
sequence "dah, dah, dah, dit, dit". Usually we use noughts and ones to represent the two
states so we can write the code for the letter "A" as "00011". Similarly, the letter "B" is represented in the code by 11001 and "C" by "01110". We call each character in the sequence a "binary digit". Over the years the term has been contracted to the word "bit".

5 bits can only represent 2**5 (2 to the power of 5), or 32, different characters, which is not enough to cover all of the characters, punctuation marks, numbers and so on in a modern Latin-European language. The Baudot teleprinters used a clever locking shift mechanism, which increased the number to 64, however this still limited the system to capital letters only and a restricted punctuation set. Hence, if you've ever seen a teleprinter message, they look a bit odd. Here is an example.

REGRET UNABLE TO TRAVEL HOME XMAS STOP LOVING YOU STOP BOYD
ENDS XXX

The "STOP" means full stop as in punctuation and the "ENDS" means end-of-message - weird huh? Nevertheless, the system was extremely successful and it survived until computer terminals and PC's displaced teleprinters in the late nineteen seventies. Baudot's name, or a portion of it, lives on in the "Baud Rate", the unit of measure for specifying the speed of a communications link. The modem on your PC probably runs at 56000 Baud (or 56Kbps, which stands for Kilo-bits per second). So, now that you know what a bit is and shortly you will learn that we use 8 of them to represent a character in a modern computer, you can work out that your modem is capable of transferring 56000/8, or 7000, characters per second. It will actually run at nothing like that speed in practice but at least you now know what the numbers mean.

5 bits is clearly not enough to represent a full language set so how man
y do we need?
Well, there are 26 characters in the English alphabet (really 53 since you need to be able to distinguish between upper and lower case and you need to cater for a space character), plus a dozen or so punctuation marks together with the numbers from zero to nine and the mathematical operators for addition, subtraction, multiplication, division and so on.

It turns out that most modern western languages (Japanese and Chinese present a whole different challenge!!) use less than 128 symbols in all so the smallest grouping of bits that we could probably get away with would be seven (since 2**7 = 128). When IBM
introduced the System/360 computer range in 1963, they decided to go with 8 bits in a
group, which gave them 256 possible values and thus plenty of "headroom" for additional
functionality. An IBM engineer named Werner Buchholz came up with the word "byte",
to describe these 8 bit groups and the word has stuck ever since.

Just as Baudot and Morse created coding systems to represent characters for their systems, we need a common standard for computers so that we can share data between them, something that would be difficult if each computer vendor used its own encoding standard.

Unfortunately, there are actually two different standards in widespread use today! Most systems use ASCII (American Standard Code for Information Interchange - pronounced "askee") but IBM, in their wisdom, chose their own proprietary system for their mainframes. It is known as EBCDIC (Extended Binary Coded Decimal Interchange Code - pronounced "ebseedik", or sometimes, "Bloody IBM!").

Your PC uses ASCII, which, being a 7-bit code, has 128 permutations (2**7). However it is implemented in 8-bit bytes (which have 256 permutations). This leaves 128 unused
combinations for special uses inside the computer. In order to avoid having to undertake the rather laborio
us task of typing out each bit value, computer engineers use Hex (Base16) to represent the eight-bit byte values. For example, the character "A" is represented in ASCII by the bit value 0100 0001. We can represent this with only two "hex" (Hexadecimal ? base 16) digits by splitting it into two as follows - 0100(4) and 0001(1), which gives 41H. The "H" denotes that we are dealing with a hex value in order not to confuse it with a decimal value. The decimal equivalent of 41H is 65 (don't worry if you didn't understand that - for now you can just think of it as a "shorthand" way of representing a longwinded binary string). The same character "A" is represented by the
bit value 1100 0001 in EBCDIC (Hex C1H).

In addition to ASCII and EBCDIC, which are used to represent textual information, there
are other code sets for Audio and Video data. MP3 and WAV are examples of two
different coding standards for compressed and uncompressed audio while JPEG and AVI
are standards for images. Despite their various flavours, all of these coding standards do the same thing; they reduce letters, colours and sounds to a string of binary digits, or bits.
As we noted at the very beginning of this piece, inside the computer is a world of nothing but binary numbers. Personally, I find that pretty sad.

Summary: