1. Why computers use binary
Bits & Bytes
Why computers use binary

2. Analog Signals Analog signals : constantly changing values
Difficult to make precise

3. Digital
Digital signals : only allowed to have specific values

4. Binary Computers are digital systems with 2 possible states: on or off
Called a binary system

5. Analog Signals
Analog values converted to binary with a threshold value

6. Analog Implementation of Binary
Even if actual values are somewhat noisy
Correct binary value is preserved

7. Why Binary Unambiguous signals (easy to tell 1 from 0)
Storing, copying data can be done without errors
Simple, easy to build
1/0 easier to build than 1/2/3/4/5/6/7/8/9/0
Anything that can be represented with some sort of pattern can be represented with patterns of bits

8. 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. …

9. Bit Patterns
One bit : 2 possible values:

10. Bit Patterns One bit : 2 possible values: 0 1
Two bits : 4 possible values

11. Bit Patterns Two bits : 4 possible values 00 01 10 11
Three bits : 8 possible values

12. Bit Patterns Four bits: 16 values Five bits: 32 values …
n bits: 2n values

13. 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

14. Bytes How many bits is 6GB? 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

15. Bytes
How many bits is 6GB? = 6 x 230 bytes = 6 x 1,073,741,824 bytes = 6,442,450,944 bytes x 8 bits per byte = 51,539,607,552 bits
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