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Bits and bytes- a primer
Wikipedia's article on binary numbers





Wikipedia's article on the history of computers





Wikipedia's article on computer data storage





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Bits and bytes
All modern computers are digital, which means that all of the information going in or coming out of them, whether it's text, images, program instructions or whatever, is converted to and dealt with as numbers.  Further, because of the way computers work, the numbers are binary, rather than the customary decimal numbers.  Probably because humans have ten fingers, we seem to have always preferred the decimal system, with ten symbols representing quantities from 0 to 9, and with each place value worth ten times the preceding place value, as in ones, tens, hundreds, thousands, etc.  Because computers are based on two-state switches that are either on or off, much like the familiar light switch, the binary, or 'base 2' system works best.  When current is flowing through a switch, it represents the number 1, and when current is not flowing, it represents the number 0.  Zeroes and ones are all there are, but in order to deal with larger numbers and more than yes-or-no and other two-state situations, the switches are arranged in groups of eight (called 'bytes') where each switch signifies the place value of a single binary digit, or 'bit.'  Binary place values are worth two times the preceding place value, as in ones, twos, fours, eights, sixteens, thirty-twos, sixty-fours and one hundred twenty-eights (to complete the byte.)  Each byte represents a number in the range of 0 to 255, or 00000000 to 11111111 as they would be written in binary numerals.  With numbers representing everything, there's a lot of converting and translating going on.  For example, the system used to represent the letters of the alphabet and all of the characters found in a typical keyboard is called the ASCII code.  The letter A is the number 65 (decimal) and written in binary notation as 01000001 (or 0-128s, 1-64, 0-32s, 0-16s, 0-8s, 0-4s, 0-2s, and 1 one.

Chips and bits and bytes
The first electromechanical digital computers were developed in the late 1930s.  The switches used in them were typically relays, similar to the familiar solenoids used to remotely unlock outer doors in apartment buildings.  In a relay, a current is applied to an electromagnet, which operates a switching mechanism mechanically.  Switch on = 1 and switch off = 0.  By the early 1940s, the clickety-click relays were replaced with significantly faster devices called vacuum tubes, which are electronic valves that moderate the flow of current through them.  Current high = 1 and current low = 0.  By the 1950s, vacuum tubes were replaced by solid state electronic valves called transistors that used a type of metal that only conducts current in one direction, called a semiconductor, instead of a vacuum.  These switches were smaller, faster, more reliable and they used less current and generated less heat than vacuum tubes.  By the 1960s, scientists had figured out how to print microscopic transistors on silicon or some other semiconductor, and were able to group thousands and eventually millions of transistors into a very small package called an integrated circuit chip.  These devices were about the size of a match head and featured switches that were faster, smaller, more reliable and used even less current than the original transistors.  Now, each year brings advances in miniaturization.  The switches get smaller and closer together.  Current has less distance to travel and so arrives more quickly, and the power of the computers based on them grows.

The math of storage
Modern computers use special integrated circuits, called memory modules, to temporarily store programs and data, but they also incorporate internal and external devices that allow for more permanent retention.  The first storage devices used cards with holes in them to represent the binary digits.  The holes were read by wires passed over the cards that either made contact behind the card if there happened to be a hole, or no contact if not.  Hole = 1, and no hole = 0.  The cards were replaced by magnetic tape that stored the digits as tiny magnets.  The magnets were formed in a magnetic kind of rust that was bonded to thin plastic called mylar.  All magnets are polarized, that is, they possess direction, and in this system a magnet polarized in one direction = 1, and one polarized in the other direction = 0.  Tape is wound past the electromagnetic tape head either forward or backward but can only be recorded or read in one direction and as a single stream on the tape.  Thus the tape system has linear access to the data in that the tape must be advanced or rewound to the specific spot where the required data sits, or to a suitable spot to begin recording.  Magnetic tape was replaced with spinning disks of the same material in a system that uses a read/record head mounted on an arm that can span the distance from the inner edge of the disk to the outer.  This system has random, near-instant access to the data and is still in use today in hard disks, though the removable kind, like floppy disks, are not used much any more.  A problem with the magnetic system is corruptibility of the data due to magnetic influence, which can come from a variety of sources, like magnets for example.

An optical system using compact discs replaced magnetic storage.  A laser is used to burn microscopic pits into the shiny surface of the disc, and another laser is used to read the pits.  A pit = 1, and still shiny = 0.  The advantages of this system include efficiency, speed, and reliability, sort of.  The jury is still out on that last one, and no one really knows how long a CD-ROM or DVD-ROM will last before errors develop.  Pits happen!

The eight-bit byte is the unit of storage, but storage capacity values, whether in memory, on a hard disk, or some peripheral device, are always given as some multiple of bytes, like kilobytes, megabytes, gigabytes or terabytes.  Now, kilo-, mega-, giga- and tera- are prefixes of Greek origin that ordinarily denote quantities in the thousands, millions, billions and trillions.  These are all decimal or base 10 values, equal to 103 (also known as 10 to the third power, or 10 X 10 X 10), 106, 109 and 1012, respectively.  But a kilobyte is a binary value equal to 210, or 1024 in base 10, and only roughly equal to 1000.  The similarly roughly equal values megabyte (220), gigabyte (230) and terabyte (240) are 1,024,576; 1,073,741,824; and 1,099,511,627,776; respectively, as decimal values.

Further reading
If you've followed along all the way to this point, embrace your inner nerd, understand that this article only scratches the surface, and do some extracurricular reading:

Tracy Kidder's The Soul of a New Machine (Little, Brown & Company, 1981) is a Pulitzer Prize-winning, nonfiction account of the design of a new generation of computer in the 1970s.  It's riveting, perfectly understandable to the uninitiated, and a great way to learn about computer processors, which haven't really changed all that much.

Wikipedia has fine, long and short articles on the topics discussed here.  Try some of the links at the left.
October 26, 2012

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