bits & bytes


b bit (binary digit): fundamental basic and smallest unit of information. capable of being 0 or 1 (i.e. can flip-flop between them).
binary: two-valued, or base-2 number system (cf. decimal: base-10 number system). 0 and 1 are the binary digits (cf. 0,1,2,...9 are the decimal digits).
All "soft stuff" (i.e. software and data) in computer is bits stored in/on/by hardware (current: flow/no flow; voltage: low/high; electrically charged/drained; magnetism: north/south; optical: pit/land). It's simpler and cheaper to design and manufacture this kind of hardware.
Digital computer, phone, camera, gadgets, appliances, car, robot etc: the real-world continuous/analog energy (light, sound, key presses, mouse movements, finger swipes, sensors' detections, etc) converted into virtual-world discrete/digital bits for processing and storage.
B byte: group/collection of 8 bits.
28=256 combinations/bit patterns:
00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 ... 11111111
(as decimal
number)
  0  1  2   3  4  5  6  7...  255

Data

Character/text/string data

each 8-bit combination (ie. each byte) is a code for a different character (letters, digits, punctuation symbols) in a text file (e.g. .txt, .html, source code) using the ASCII code: A=01000001 a=01100001 ...
A 2-byte code: Unicode has all the symbols of all human writing systems.

Numeric data

mostly stored as 4 bytes per number: two types:

Integers (2's complement format)

whole numbers, positive and negative, for counting. Range from -2 billion to +2 billion (-2G—2G-1)
 123: 00000000000000000000000001111011
-123: 11111111111111111111111110000101 
Binary number: two digits are 0 and 1 (cf. decimal: ten digits 0..9).
columns(places) are powers of 2 (cf. decimal: columns are powers of ten)

Negate by complementing then adding 1.
8-byte "long" (64-bit) range from -64E to +64E

Real numbers (IEEE 754 floating-point format)

numbers with decimal point, for measurement.
 123.0: 01000010111101100000000000000000
-123.0: 11000010111101100000000000000000
  1.98: 00111111111111010111000010100100
 -1.98: 10111111111111010111000010100100
 
Inf: 01111111100000000000000000000000
NaN: 01111111111111111111111111111111
8-byte "double" gives greater range and precision.
CPU ALU has separate circuitry for procesing integers and floating-point data.

Media files (image, sound/audio, video) are mostly (integer) numbers that represent the color and intensity/brightness of pixels/dots or pitch/frequency and loudness of sound.
Data files (e.g. spreadsheet, database) might contain these numeric types of data.

Software

CPU/machine instructions are variable-lengthed complexly-coded bit strings.
Example (MIPS CPU [simple one]):

CPU/processor "knows how" to execute/do these instructions/"orders".
Software is a sequence of instructions flowing into the CPU for execution, telling CPU what operations to perform on what data.

Sizes

prefix Greek English either 103n or 210n
K kilo thousand 1,000 103 1,024 210
M mega million 1,000,000 106 1,048,576 220
G giga billion 1,000,000,000 109 1,073,741,824 230
T tera trillion 1,000,000,000,000 1012 1,099,511,627,776 240
P peta quadrillion 1,000,000,000,000,000 1015 ... 250
E exa quintillion 1,000,000,000,000,000,000 1018 ... 260
m milli thousandth .001 10-3
μ micro millionth .000001 10-6
n nano billionth .000000001 10-9

File sizes:
This prefixTable.html file is about 4KB
Alice in Wonderland 148 KB
Bible 4.2 MB as a txt file.
Word document: 20KB. Excel workbook: 15KB. Access database: 500KB
Typical digital photograph (JPEG): 1-10 MB

Hardware storage capacities:
Installed RAM/(main, primary)memory on a new basic computer: a few GB
Start | Computer (right click) | Properties shows amount of RAM.
This PC | (right click) | Properties shows amount of RAM.
Size (storage capacity) of a hard disk drive: maybe 500 GB, or 1 TB
Windows Explorer | C drive (right click) | Properties
USB flash memory thumb drive: 1, 2, 4, 8, 16, 32, 64 GB (note: powers of 2)

Hz hertz: cycles per second. frequency. "ticks" per second. CPU has an internal metronome that pulses electricity, driving the rest of the circuitry; "speed" of the CPU.
Typical CPU clock rate: 2.2 GHz

bps bits per second: "speed" (bandwidth) of network.
Typical cabled (Ethernet): 100 Mbps or 1000Mbps=1Gbps (Gigabit)
Typical WiFi wireless: a few tens Mbps
Typical Internet access (DSL, cable modem): a few Mbps; fiber optic: few 10s Mbps

s second: ms (milliseconds) μs (microseconds) ns (nanoseconds)
hard disk access: ~10ms. RAM access: ~50ns. Cache access: ~10ns.
ping (connectivity check) to LAN: a few ms; to "far" Internet: up to 500ms