Analysis of GIS Data by Simple Examination - Introducing Geographic Information Systems with ArcGIS - page 350

Input

When you press and hold the Shift key and then press the K key on a computer keyboard, a string of
bits 2 is sent to the computer. When you move the mouse pointing device, sequences of bits are sent to the
computer. When you speak into a microphone attached to your computer's sound card, a string of bits is
generated by the sound card (also a computer, by the way) and winds up in the computer's store.

Representation

For a computer to do computation the way humans like it done, it has to represent decimal (base ten)
numbers in binary (base two). Here are some decimal numbers and their binary equivalents:

Base Ten Base Two

0 00000

1 00001

2 00010

3 00011

4 00100

5 00101

6 00110

7 00111

8 01000

9 01001

10 01010

11 01011

12 01100

13 01101

14 01110

15 01111

16 10000

Given a number in base ten, you may interpret it in this way: Starting from the right and summing the
values, the first position represents the number of 1s, the second position represents the number of 10s,

2 Assuming that the computer uses the most commonly accepted convention of the relationship of characters,
such as “K,” to bits—namely the American Standard Code for Information Interchange (ASCII)—the string of bits
sent from the keyboard to the computer would be 11010010. Such a string of 8 bits is called a byte. The size of a
computer's memory and disk storage is commonly expressed in terms of bytes—always a whole lot of them. A
kilobyte is 1024 bytes. A megabyte is 1024 kilobytes. A gigabyte is 1024 megabytes. A terabyte is 1024 gigabytes.
A petabyte is 1024 terabytes. An exabyte is 1024 petabytes. Some hard drive manufacturers cheat and call a kilobyte
1000 bytes, a megabyte 1000 kilobytes, and so on, thus inflating the advertised hard drive capacity. Check the Internet
for more information on this scuffle.