When you have finished this project, you will be able to:
	describe analog data
	describe digital data
	describe the difference between digital and analog data
	describe why computers need digital data
	count using the binary number system
	describe the following terms: Bit Byte MODEM analog digital

• analog = continuous
• digital = step-by-step (discrete)

In order to understand the digital world - the world of computers and other electronic devices, you first need to be able to understand the "non-digital" world - the world in which we live everyday. Humans are not digital creatures - in other words, we do not function like computers do. For us, life is analog - a representation of things and events along a continuum. For example, examine the illustration below. The sweep hand moves continuously, providing a representation of time passing. However, you have no idea how much time has passed. Even if there were numbers on the face of the sweep hand, the precise amount of time would depend upon the accuracy of the number placement on the face, your angle of viewing, and any number of other factors. In the digital example, there is no question as to how much time has passed.

How do you tell someone else what you observe? You have a "feeling" for the time in the analog example above, just as we have a "feel" for the temperature, or the amount of light, but it is difficult for people to render precise values and when we communicate the time or the temperature we convert from our feeling of the temperature to a discreet value for the temperature - but we would seldom be correct; close perhaps, but not precise.

From the examples shown above your can deduce that analog data is continuous - a wave form. This is analog data

Digital data is a representation of something at a particular instant in time. This is digital data

Humans are used to counting and representing numerical values using the decimal system - a base 10 counting system. The decimal counting system is derived from the Latin term decem which means ten. We all learned to count this way as we were growing up. If you look at a typical number, you can see there are place values. For example, use the number, 1560.

The right hand digit, the 0, holds the ones place, the second digit from the right, then tens place, the third digit from the right, the hundreds place, and the fourth digit from the right holds the thousands place. We would read this number as one thousand, five hundred and sixty. In the decimal number system, the values are in powers of ten. Mathematically, we could use a base 10 number system to express 1560 by using this expression:

However, the decimal number system will not work with computers. This is because computers only understand two states which requires the use of a base 2, or binary number system. The binary number systems makes use of only two digits: 0 and 1. The values in the binary system are in powers of two, just as the values in the decimal number system are in powers of ten. For example, the base 10 number 5 can be represented by the binary number 101, or:

Each bindary digit is called a BIT - from binary digit. BITs are assembled in a manner similar to the way we in which we form words from individual letters. BITs are assembled in groups of eight to represent a number or letter called a BYTE. Every alphanumeric character that we use has an equivalent BYTE. For example the number 0 is represented by the group of 8 BITs (1 BYTE):

The chart below illustrates some other binary numbers as expressed in BYTES:

We need to know this because everything we do is assigned a value. The values are assigned using a standard protocol specified by the American National Standards Institute (ANSI), and are called American Standard Code for Information Interechange (ASCII). The ASCII character set does not vary from computer to computer and ASCII assigns a code for each letter of the alphanumeric characters on the keyboard. For example, the ASCII code for the letter A is 65, and is represented by the binary code 01000001. You will recall this conversion to binary code is required because computers and other digital devices can only understand BITs of information.

Another application of conversion from analog to digital data is in data communications. Data communications occurs on computer networks - you will learn more about this in another lesson. However, when computers communicate with each other using telephone lines, which are analog devices, a "translator" must be used to convert the data from digital information - which the computer generates, to analog information - which the telephone can understand and back again. This is done with a device called a MODEM which stands for MODulator-DEModulator. Most home users use a MODEM to communicate with other computers or to connect to the Internet. The illustration below demonstrates how a MODEM works:

You should take some time at this point to think about other examples of analog to digital conversions that are used in the computing industry. On the quiz for this unit, you will be required to provide another example.

You are familiar with the metric prefixes kilo to designate 1000 and mega to designate 1,000,000. The same prefixes are used in the computer industry when specifying the sizes of such items as computer memory or hard drive space. You have already learned that bytes are used as "words" when working with computers. The sizes of disks and memory are measured in bytes. For example, a computer might have 64 megabytes (64 MB) of RAM. When using computers and other digital devices, MB represents megabytes, and is 220 (2 to the power of 20), or 1,048,576. In a similar manner, the prefix giga is 230, or 1,073,741,820 bytes. Using this information, you can see that 64 MB of RAM is actually 64 X 220 which equals 67,108,864 bytes.

Understanding and using bits and bytes is far more complex than presented in this short introduction on Data Representation, and if you plan on going into Computer Engineering or Computer Science, you will learn and use this information often. However, for the purposes of this course, a basic understanding is enough. If this topic interests you, you should seek out books and Web references about digital electronics, digital circuits, and logic circuits.

Test Your Knowledge

Click here to download the worksheet for this unit which is a Word file. Answer the questions directly on the worksheet, save it on your personal drive, then email it as an attachment to your teacher.