Unit — Mechanical Sympathy

01how

A 4 GHz core stalls 80 ns on a cold miss. Roughly how many instruction slots evaporate?

1. a~30
2. b~80
3. c~320
4. d~4000

02why

Why is SoA mandatory for hot loops rather than a stylistic preference?

1. aIt looks cleaner and is easier to maintain
2. bIt makes the loop's memory access pattern match what the cache hierarchy fetches — one line delivers many useful iterations instead of one
3. cThe C# compiler requires it for structs
4. dIt uses less total memory

03why

Why can't a parallel IJobEntity call EntityManager.AddComponent directly?

1. aEntityManager isn't Burst-compatible
2. bA structural change moves entities between chunks, invalidating memory other worker threads are reading right now
3. cIt would simply be too slow
4. dIt can, with [NativeDisableParallelForRestriction]

04howmeasure

Build a chunk-capacity probe: an archetype summing 48 bytes/entity. How many entities pack into one 16 KB chunk on your build?