Why Hexadecimal?
Part of the Fundamentals section of Coddy's Assembly journey — lesson 10 of 45.
You now know that computers use binary. So why do assembly programmers rarely write binary directly?
The problem with binary:
Binary numbers are very long. Look at this example:
| Number | Binary |
|---|---|
| 255 | 11111111 |
| 1000 | 1111101000 |
| 65535 | 1111111111111111 |
Writing long strings of 1s and 0s is slow, error-prone, and hard to read.
The solution: hexadecimal (base 16).
Hexadecimal (or "hex") uses 16 symbols:
| Digit | Value |
|---|---|
| 0-9 | 0 to 9 |
| A | 10 |
| B | 11 |
| C | 12 |
| D | 13 |
| E | 14 |
| F | 15 |
Why hex is perfect for computers:
One hex digit represents exactly 4 bits (half a byte).
| Bits | Hex digits needed |
|---|---|
| 4 bits (nibble) | 1 hex digit |
| 8 bits (1 byte) | 2 hex digits |
| 16 bits (2 bytes) | 4 hex digits |
| 32 bits (4 bytes) | 8 hex digits |
| 64 bits (8 bytes) | 16 hex digits |
Same number, three ways:
| Decimal | Binary | Hexadecimal |
|---|---|---|
| 255 | 11111111 | FF |
| 1000 | 1111101000 | 3E8 |
| 65535 | 1111111111111111 | FFFF |
Notice how much shorter hex is than binary.
Where you will see hex in assembly:
- Memory addresses (like
0x7FFFor0x402000) - ASCII codes (like
0x41for 'A',0x0afor newline)
- Register values in debuggers
- Color values (like
0xFF0000for red)
Hex is written with a prefix:
| Prefix | Example | Meaning |
|---|---|---|
0x | 0xFF | FF in hex (255 in decimal) |
$ | $FF | Same thing (used in some assemblers) |
h | FFh | Same thing (older style) |
In this course, we use 0x prefix: 0x0a, 0x41, 0xFF.
Try it yourself
This lesson doesn't include a code challenge.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Fundamentals
1The Machine
What is CPUMemoryRegisters vs MemoryHow instructions workTwo-File PatternThe x86-64 Architecture
2Number Systems
Why Binary?Binary NumbersDecimal to BinaryWhy Hexadecimal?Hex to DecimalDecimal to HexASCII & Hex