C#: What is the difference between Span<T> and Memory<T>?

Span<T> — stack only. Memory<T> — stack or heap.

Span<T>:

• Stack only.
• Ref struct.
• Not async.

Memory<T>:

• Stack or heap.
• Regular struct.
• Async safe.

1// Span
2Span<char> span = stackalloc char[256];
3"Hello".AsSpan().CopyTo(span);
4
5// Memory
6Memory<byte> buffer = new byte[1024];
7await stream.ReadAsync(buffer);

Key: Span for sync, Memory for async.