> Yes, a Dataspace is a sort of address space, with its > own page and segment tables, but with no internal > structure (private region, CSA, LPA etc), just storage > for data. Any structure you have to add with your own > program code. > > Generally speaking its simpler and more efficient > nowadays to use 64 bit storage which provides similar > space expansion and sharing capabilities in a linear > address space.
That said, there are circumstances where the opposite may be true: that a hyperspace may provide better performance than 64-bit storage. I had a case recently, with a program that generates large amounts of data that it needs to hold temporarily in storage. I tried both ways, and found that a hyperspace gave better performance. The reason, I eventually decided, was that the data had to be initially read from a dataset -- and thus had to be read into 31-bit storage -- and later written back to a dataset -- again, having to be written from 31-bit storage. When it came to storing the data away, the overhead of copying it above the bar, and later copying it back again, was greater than the overhead of leaving it where it was and using a hyperspace. If I'd been able to create, and later consume, the data entirely in 64-bit storage, the reverse would probably have been true. Allen Gainsford Info Developer, Banking Shared Services HP Enterprise Services (South Pacific)
