What is DS memory used for?

Can someone tell me exactly what DS memory is actually used for? Yes, I know it's for DS queries, but what does it hold? Session blocks? Execution paths? Data? Temp data? Sort files? And how exactly does the amount you have affect a query? Can anyone explain exactly what was going on when, when I added a CPU VP, certain queries got a -208 unless either I increased DS_TOTAL_MEMORY, or dropped PDQPRIORITY below 75? OK I can get the general gist from these diagnostics alone, but what are the conditions that cause the query to go pop, and what are thee benefits of increasing DS_TOTAL_MEMORY above this? Andy