Some worthwhile sites that annotate and collect even older material are listed here. They often cross-reference each other, but are big. These are some that I've found worth exploring.
alpha = t1/t2,
where t1 is the time taken to read a chosen address of the store,
and t2 (>= t1) is the time elapsing between the demand for that
information being made, and the end of the reading process.
Clearly, it is necessary that the part of the storage to which access is
frequently made should have a value of alpha approaching the
optimum value of unity, if the time taken in solving a problem
is not to be extended by barren periods of waiting. In the electronic
storage system1 used, alpha = 1. However, it is unnecessary to
have alpha = 1 for all the storage, and, in fact, a magnetic storage
system, for which alpha = 1/133, is used to supplement the electronic system.
An important feature of any storage system is its accessibility ratio
The "electronic" storage system was a Williams CRT storage tube; the "magnetic storage" system referred to a drum memory, which (in this paper) is later footnoted with a reference to unpublished work by West and Thomas. We have here both the notion of a storage hierarchy, and, one suspects, some hardware that wasn't quite working yet.