C#: What is the difference between ArrayPool and ObjectPool?

1// ArrayPool
2var pool = ArrayPool<byte>.Shared;
3var array = pool.Rent(1024);
4try { /* use array */ }
5finally { pool.Return(array); }
6
7// ObjectPool
8var pool = new DefaultObjectPool<StringBuilder>();
9var sb = pool.Get();
10try { /* use */ }
11finally { pool.Return(sb); }