Download Pathway Introduction: Information Technology

Bits & Bytes
Why computers use binary
Analog Signals
• Analog signals : constantly changing values
– Difficult to make precise
Digital
• Digital signals : only allowed to have specific
values
Binary
• Computers are digital systems with 2 possible
states: on or off
– Called a binary system
Analog Signals
• Analog values converted to binary with a
threshold value
Analog Implementation of Binary
• Even if actual values are somewhat noisy
• Correct binary value is preserved
Why Binary
1. Unambiguous signals (easy to tell 1 from 0)
– Storing, copying data can be done without errors
2. Simple, easy to build
– 1/0 easier to build than 1/2/3/4/5/6/7/8/9/0
3. Anything that can be represented with some
sort of pattern can be represented with
patterns of bits
Bits
• Bit : single on/off value
• Represented as:
–
–
–
–
–
A mechanical electrical switch.
Voltage on a wire.
Magnetic field of a small slice of metal.
A hole punched in a card.
A tiny part of the light-reflecting
surface of a CD.
…
Bit Patterns
• One bit : 2 possible values:
0
1
Bit Patterns
• One bit : 2 possible values:
0
1
• Two bits : 4 possible values
00
01
10
11
Bit Patterns
• Two bits : 4 possible values
00
01
10
11
• Three bits : 8 possible values
000
100
001
101
010
110
011
111
Bit Patterns
• Four bits: 16 values
• Five bits: 32 values
• …
n bits:
n
2
values
Bytes
• 1 bit (1/0) usually not useful on its own
• Usually work in larger chunks
– Byte : 8 bits
– Special names for large collections of bytes:
Name
Number of Bytes
power of 2
byte
1
20
kilobyte (KB)
1024
210
megabyte (MB)
1,048,576
220
gigabyte (GB)
1,073,741,824
230
terabyte (TB)
1,099,511,627,776
240