Why use float and double instead of real?

[BCS]

Hello Don,

> Size. Since modern CPUs are memory-bandwidth limited, it's always
> going to be MUCH faster to use float[] instead of real[] once the
> array size gets too big to fit in the cache. Maybe around 2000
> elements or so.

I was under the impression that the memory buss could feed the CPU at least 
as fast as the CPU could process data but just with huge latency. Based on 
that, it's not how much data is loaded (bandwidth) but how many places it's 
loaded from. Is my initial assumption wrong or am I just nit picking?