Skip to content
cyber journey
Code (2nd ed.)Help DeskTryHackMeA+ Core 1The Linux Command LineLearn Windows PowerShellNetworking for Sysadmins
Ch. 1Ch. 2Ch. 3Ch. 4Ch. 5Ch. 6Ch. 7Ch. 8Ch. 9Ch. 10Ch. 11Ch. 12Ch. 13Ch. 14Ch. 15Ch. 16Ch. 17Ch. 18Ch. 19Ch. 20Ch. 21Ch. 22Ch. 23Ch. 24Ch. 25Ch. 26Ch. 27Ch. 28

Resource Cheatsheet

Code: Bytes and Hexadecimal

Code ch. 12 — the 8-bit byte, nibbles, hexadecimal digits and conversion, hex notation, and where hex appears in everyday IT.

Updated
Reading time
3 min read
Detail
Code (2nd ed.)
Detail
Ch. 12
On this page

In one line: computers group bits into 8-bit bytes, and hexadecimal writes each byte as exactly two digits — the shorthand you’ll read for the rest of your career.

Companion to: Charles Petzold, Code (2nd edition), chapter 12. See also TCM Help Desk section 3.

Bytes

Unit Size Values
Bit 1 2
Nibble 4 bits 16 → one hex digit
Byte 8 bits 256 → two hex digits (00–FF)
16-bit word 2 bytes 65,536 (0000–FFFF)

IBM popularised the 8-bit byte in the 1960s. It’s big enough for a character and splits neatly into two nibbles.

Hexadecimal (base 16)

Hex 0–9 A B C D E F
Decimal 0–9 10 11 12 13 14 15
  • Hex → decimal: 2F = 2×16 + 15 = 47.
  • Binary → hex: split into nibbles. 1010 1111 = A F = AF.
Notation Where
0x2F C, Python, PowerShell, most code
2Fh Assembly, older docs
#2F CSS colours (#FF0000 = red)
&H2F Visual Basic
2f Hashes and dumps — usually lowercase, no prefix

Where you’ll meet hex

Thing Example Size
MAC address 00:1A:2B:3C:4D:5E 6 bytes (48 bits)
IPv6 address 2001:db8::1 16 bytes (128 bits)
SHA-256 hash 64 hex characters 32 bytes (256 bits)
Colour #1E90FF 3 bytes (red, green, blue)
Memory address 0x7FFE4A20 Depends on architecture
Windows error code 0x80070005 (access denied) 4 bytes

Try it

'{0:X2}' -f 47                     # 2F
0x2F                               # 47
Format-Hex .\file.bin              # hex dump
Get-FileHash .\file.bin            # SHA-256, shown in hex
printf '%02X\n' 47                 # 2F
echo $((16#2F))                    # 47
xxd file.bin | head                # hex dump
sha256sum file.bin

🔐 Security and IT connections

  • Hex is the language of investigation: file signatures (4D 5A = Windows executable), packet bytes in Wireshark, hash values in threat intel, and memory addresses in crash dumps.
  • Hashes are compared as hex strings. One changed byte gives a completely different hash — check downloads against the vendor’s published value.
  • Error codes decode to meaning. Search 0x80070005-style codes exactly as shown.

Practice drills

1. Convert 0xC8 to decimal.

12×16 + 8 = 200

2. How many hex characters is an MD5 hash (128 bits)?

128 ÷ 4 = 32

3. Write binary 0011 1010 in hex.

3A

Key takeaways

  • Byte = 8 bits = two nibbles = two hex digits.
  • Hex digits run 0–F; convert binary by grouping into fours.
  • MAC addresses, IPv6, hashes, colours and memory addresses are all hex.

Search

Filter by collection