Checkpoint — archetypes & chunks

01why

An entity currently has {LocalTransform, Health}. You call AddComponent<Velocity> on it. What physically happens to the entity's data?

1. aA Velocity field is appended in place; the other components stay put
2. bThe entity's existing components are copied from its old chunk to a chunk of the new {LocalTransform, Health, Velocity} archetype, and the old slot is freed
3. cNothing moves; the entity gains a pointer to a separate Velocity array
4. dThe whole chunk is reallocated to make room for Velocity

02why

Why does the runtime group entities by their entire component *set* rather than by a single component type?

1. aTo save memory by deduplicating component values
2. bSo that for any combination of components an archetype has, each component's array is dense and parallel — making every query over any combination cache-friendly and vectorizable
3. cBecause C# generics require a single concrete type per collection
4. dTo make entity IDs shorter

03why

Your archetype's components sum to 96 bytes per entity. What ChunkCapacity will Unity report, and why?

1. a~170 — (16384 − 64) / 96
2. b~156 — the 8-byte Entity handle raises per-slot cost to 104
3. c128 — the bytes would allow ~156, but the enableable-bitmask cap clamps capacity
4. d~48 — each component array pads to a full cache line per entity

04why

A hot archetype carries a 128-byte component that your main loop never reads. Since SoA means the loop doesn't stride over it, what is the actual cost?

1. aThere is no cost — SoA makes unread components entirely free
2. bThe loop must skip past 128 bytes per entity, slowing iteration
3. cIt lowers chunk entity-capacity, so every query over that archetype spreads across more chunks and packs fewer entities per line of the components it does read
4. dIt forces the loop to run single-threaded

05how

Why is 16 KB — rather than, say, 512 KB — a sensible chunk size?

1. a16 KB is the maximum a single struct may occupy in C#
2. bIt keeps a chunk's streaming working set inside fast L1/L2 cache while still amortizing per-chunk header and iteration overhead; much larger chunks stop fitting cache and coarsen parallel work
3. cIt matches the operating system's virtual memory page size exactly
4. dLarger chunks would exceed Burst's stack limit

06what

What does the Entity value itself contain?

1. aThe entity's component data, inline
2. bA pointer to a managed C# object representing the entity
3. cAn index and a version number — a handle the runtime uses to locate the entity's components
4. dThe archetype's full component list