BitLab

Bits are tiny light switches

A computer only understands two things: ON and OFF. One switch is called a bit. Eight bits together make a byte — and a byte can store a number. Try it: click the switches!

Decimal

Hex

ASCII

NUL

Flip some switches to make a number…

It works just like decimal — but doubling instead of ×10

You already know place-value columns from normal numbers: units, tens, hundreds. Each column is worth 10× more. Binary is the same idea, but each column is worth 2× more: units, twos, fours, eights…

These tables show your lightbulb number from above — flip the switches and watch both sides follow!

Decimal — powers of 10

10²	10¹	10⁰
hundreds	tens	units
0	0	0

0 = 0×100 + 0×10 + 0×1

Binary — powers of 2

2⁷	2⁶	2⁵	2⁴	2³	2²	2¹	2⁰
128s	64s	32s	16s	eights	fours	twos	units
0	0	0	0	0	0	0	0

00000000 = 0

Hex — powers of 16

Same trick a third time — each column is worth 16× more. A whole byte fits in just two hex digits!

16¹	16⁰
sixteens	units
0	0

00 = 0×16 + 0×1 = 0

💡 Reading trick: write the column values above the bits (128, 64, 32, 16, 8, 4, 2, 1), then just add up the columns where the bit is 1.

Powers of 2 — worth memorising!

These numbers appear everywhere in computers (ever noticed games and phones use 256, 512, 1024…?). Hover over a number to see it as a square of dots!

2⁰	2¹	2²	2³	2⁴	2⁵	2⁶	2⁷	2⁸	2⁹	2¹⁰
1	2	4	8	16	32	64	128	256	512	1024

With 8 bits you can make every number from 0 (all OFF) to 255 (all ON). That's why so many computer things stop at 255!

Hexadecimal — binary's shorthand

Binary is long to write: 11111111 is a lot of typing for 255! Programmers use hexadecimal (hex): counting with 16 symbols — 0–9 then A B C D E F. One hex digit replaces exactly 4 bits.

Split a byte in half → two hex digits

Flip the switches. Each group of 4 bits (a nibble) becomes one hex digit.

Left nibble

Right nibble

Hex

0x00

Decimal

The lookup table — 0 to 15

💡 Programmers put a tag in front of a number to say which system it's in: 0x means hex (like 0xFF = 255) and 0b means binary (like 0b1111 = 15). Without a tag, 10 is confusing — is it ten, 0b10 (two), or 0x10 (sixteen)? The tag tells you! You've seen hex before, by the way: colour codes like #FF8800 are three hex bytes — red, green, blue.

ASCII — how letters become numbers

Computers can only store numbers. So long ago, everyone agreed on a code: A = 65, B = 66, C = 67… and small letters a = 97 onwards. That agreement is called ASCII. Every letter is one byte.

Type something — watch it turn into bytes

Show the full ASCII letter table

🔎 Spot the pattern: capital A is 01000001 and small a is 01100001. Only one bit is different (the 32s column)! That single bit is the difference between BIG and small letters.

Secret code machine

Now you know the whole chain: letter → ASCII number → binary. That means you can write messages nobody else can read — unless they know binary too. Send one to a friend and teach them to decode it!

🔒 Encode a message

🔑 Secret key

Binary Hex

Your coded message appears here…

🔓 Decode a message

Paste binary (groups of 8) or hex (pairs) — spaces optional. It auto-detects which one it is.

🔑 Secret key

The secret message appears here…

⚡ How the lock works — XOR

The lock uses an operation called XOR (say "ex-or"). It compares two bits and asks one question: are they different?

message bit	0	1	1
key bit	1	0	1
result	1	1	0

Try it — flip any switch and watch the bottom row light up exactly where the two rows above disagree:

message byte

key byte

locked byte = message ⊕ key

The magic: XOR with the same key twice brings the message back. Lock it: message ⊕ key. Unlock it: locked ⊕ key = message again. That's why you and your friend just need the same key.

🎖️ The unbreakable code: if your key is random, as long as the message, and never used twice, this becomes a one-time pad — the only cipher in the world that's mathematically impossible to crack. Real spies carried little pads of random keys and burned each page after one use!

🕵️ First mission

Decode this message by hand with the ASCII table (no pasting — that's cheating!):

01011001 01001111 01010101 00100000 01010010 01001111 01000011 01001011

Bits are tiny light switches

It works just like decimal — but doubling instead of ×10

Decimal — powers of 10

Binary — powers of 2

Hex — powers of 16

Powers of 2 — worth memorising!

Watch binary count — see the pattern tick

Hexadecimal — binary's shorthand

Split a byte in half → two hex digits

The lookup table — 0 to 15

ASCII — how letters become numbers

Type something — watch it turn into bytes

Secret code machine

🔒 Encode a message

🔓 Decode a message

⚡ How the lock works — XOR

🕵️ First mission

Play — test your skills