Alignment

Think of parking spots painted for specific car sizes. A sedan fits cleanly in a sedan-sized spot. Park a truck across two spots and you’ve blocked traffic.

aligned:                      misaligned:
│────│────│────│              │────│────│────│
0    8    16                   0    4    12
     ▲                              ▲
 fits in 1 spot               straddles 2 — slow

Compilers insert padding between struct fields so every field lands on its proper boundary.