1. 0110101001101101 10010110 2/4 Binary Code & CPUs Digital Signals
digital versus analog, examples
Binary Numbers
Transistors: introduction
Binary Code
bits & bytes
types: ASCII, UNICODE, EBCDIC

2. Digital Signals: why they are discussed.
Virtually everything in a computer runs in a digital system: data storage, communication, output on the screen, …
Everything is in its lowest form either ON or OFF, UP or DOWN, YES or NO.
Bits & bytes are combinations of digital signals and codes.

3. Digital Signals: what are they?
Digital signals have two settings: ON or OFF.
Examples: smoke signals, Morse code, fluorescent lights, pass or fail
Anything that can be compared to ON or OFF can be a digital signal:
Magnets: north or south
Voltage: high or low
Light: light or dark
Gates: open or shut

4. Digital Signals versus Analog Signals
Digital signals have two settings: ON or OFF.
Analog signals have ranges of settings: dimmer switches, human voices, ocean waves
Sound: Digital versus analog.
Analog is a wave: continuous, gradual
Digital is a step: non-continuous, ON/OFF
Analog signal
Digital signal

5. Binary Numbers A digital system
Can represent any decimal number with only two characters: 0 & 1
Why not use decimal numbers? Computers use digital systems (on or off)
Decimal Binary

6. Transistors: tiny ON/OFF switches
Tiny electrical gates with two paths: 1. Control path (gatekeeper) 2. Signal path (goes through gate)
Only two possible states: gate is OPEN or gate is CLOSED.
Transistors are what make up computer chips.
AMD Athlon chip has 22 million transistors.
Image courtesy of AMD

7. Binary Code: Bits & Bytes
Bit: a single element of code. 0 or 1.
Contraction of “Binary digit”
Byte: a collection of 8 bits
Possible number of different bytes: etc.

8. Binary Code: Bits & Bytes
Each byte represents 1 character or command.
A simple text file ( log.txt ) can be only a few hundred bytes. A spreadsheet ( book1.xls ) can be millions.
kilobyte: KB 2 to the 10th (1,024) bytes. megabyte: MB 2 to the 20th (1,048,576) gigabyte: GB 2 to the 30th (1,073,741,824) terabyte: TB 2 to the 40th (1,099,511,627,766)

9. When is a kilobyte NOT a kilobyte?
Common usage (not exactly correct, but close)
kilobyte: KB 1,000 bytes megabyte: MB 1,000,000 bytes gigabyte: GB 1,000,000,000 bytes terabyte: TB 1,000,000,000,000 bytes

10. Why we don’t type in binary digits.
Codes (lookup tables) in the computer.
Each character corresponds to a byte.
As we type, the keystrokes are translated into bytes by the computer.
The computer reverse-translates to show the characters on the monitor.
Common code sets: ASCII, UNICODE, EBCDIC

11. Code Types.
ASCII “As-key” American Standard Code for Information Interchange.
1st half of the slots in the table are for “standard” ASCII characters. The second half contains the “extended” ASCII character set.
UNICODE uses 2 bytes/char rather than 1.
Supports many more characters (34,168). Esp. used for non-English languages
EBCDIC “eb-see-dik” Extended Binary Coded Decimal Interchange Code.
Mainly used on mainframe computers