bit

toc =What is a Bit?= In computer terms, a bit is a single piece (bit) of information. This can be thought of in any way you like: as one or zero, true or false. This makes up the system of binary that computer use.

=Sizes= The term bit was defined in the creation of computers. Other measurements of data are made in relation to it:

Note that there is always a bit of confusion as to how sizes should be displayed. The standard (as far as this writer is concerned) is to write a small b for a bit, and a large B for a byte. Another standard that arose was to do the reverse, keeping the B capitolised and changing the k, m, or g respectively to capitols depending on which was meant. The world standards body last year agreed that in the future, sizes should be written with an i for bytes, and none otherwise. This would make KB and KiB, MB and MiB, GB and GiB. Many (including this author) don't use that method still.
 * Name || Size ||
 * bit || 1 ||
 * byte || 8 ||
 * Kilobit (Kb) || 1000 bits ||
 * kilobyte (KB) || 1,024 bytes, 8192 bits || ||
 * megabit (Mb) || 1,000,000 bits ||
 * megabyte (MB) || 1,024 kilobytes, 8,388,608 bits ||
 * gigabit (Gb) || 1,000,000,000 bits || ||
 * gigabyte (GB) || 1,024 megabytes, 8,589,934,592 bits || ||

Advertising agencies have used this confusion to their advantage. A standard recordable DVD-R is marked 4.7GB. Many are confused when they find out that this dvd only holds 4.37GiB. 4.37GiB is 4,700,000,000 bits, which is what the company is refering to in order to make their media sound larger.

=Representations= Binary (digital) data can be represented in many different ways, as seen by the plethora of formats now available.

TTL
Circuitry such as that found in a computer functions on TTL logic. This is just a fancy way of saying that a zero is represented by a small (in the range of 0.3) volts of electricity, and a one is represented by +5 volts.

Serial
The serial port (that old 9 pin port on the back of a computer) represents bits in a different way. This uses -8 volts as a one, and +8 volts as a 0. Zero volts means the serial port isn't working. This method is known as inverted logic. This is a problem for circuitry hobbyists who wish to make simple computer interface boards. In order to do so they usually have to convert the signal to TTL, by using an integrated circuit like the [|MAX232] (made by maxim electronics and copied by texas instruments).

CDs and DVDs
CDs and DVDs represent data by using small etchings in the plastic of the surface of the media. This "pit" is picked up when it's reflected by a laser onto a reader. A small pit represents a zero, a large pit a one. DVDs have these pits much closer together than CDs.

Burnable Media
Burnable media works the same way as above, except instead of pits, dark (and very exact) blotches are burned into a special dye by a laser. This looks like a pit to a regular CD or DVD reader.

Hard Drives
Hard drives and floppy drives such as 3 1/2" use high density metals or plastic materials that can hold a magnetic charge. A magnetic reader and writer (akin to that used in a cassette tape player, though much more exact) moves over the surface, reading the magnetic charge. A low magnetic charge is considered a zero, while a high signal is considered a one.

Flash Drives
Flash memory (such as that in your cell phone, PDA, mp3 player, usb key, etc) stores data by trapping electricity in insulated cells of transistors, and attempts to pass electricity through them at read time. If the transistor lets the electricity through, a one is returned; if not, this is a zero.