Transcript 9/13 Binary Numbers, Digital Signals, & Binary Code

2/4 Binary Code & CPUs
• Digital Signals
– digital versus analog, examples
• Binary Numbers
– Transistors: introduction
• Binary Code
– bits & bytes
– types: ASCII, UNICODE, EBCDIC
01101010011
01101
10010110
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.
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
Digital Signals versus Analog Signals
• Digital signals have two
settings: ON or OFF.
• Analog signals have
Analog signal
Digital signal
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
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
0
1
2
3
4
5
6
7
8
9
10
11
12
Binary
0
1
10
11
100
101
110
111
1000
1001
1010
1011
1100
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
Binary Code: Bits & Bytes
• Bit: a single element of code. 0 or 1.
– Contraction of “Binary digit”
• Byte: a collection of 8 bits. 00000000.
– Possible number of different bytes: 256
00000000 00000001 00000010 00000011 00000100
00000101 00000110 00000111 00001000 00001001
00001010 00001011 00001100 00001101 00001110
00001111 00010000 00010001 00010010 00010011
00010100 00010101 00010110 00010111 00011000
00011001 00011010 00011011 00011100 00011101
00011110 00011111 etc.
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)
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
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
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