Hi Margeret,

My point was that the additional RAM should make the second step faster *than if there was no RAM* (not compared to the first step) since the table is read from RAM rather than from disk,(and even if the cache flush during output negates some of the gains).

On the topics optimising access speed, in my experience, any procedure accessing large data sets can be sped up by properly setting the reading options. Here is a benchmark (details in the book) where the read time using SAS defaults is 1.96s seconds. The wrong options can slow it down to almost 10s (top left of table) , the right ones can speed it up to 0.4s (bottom right).

BUFNO 1 5 25 100 500
BUFSIZE SGIO
0 no 1.96
4k no 2.41 2.62 1.66 1.65 1.67
yes 9.62 6.09 1.55 1.18 1.39
8k no 2.19 1.13 1.68 1.22 1.25
yes 5.40 3.20 1.19 1.02 0.45
16k no 1.04 1.04 2.77 1.15 2.60
yes 3.18 1.91 0.62 1.09 0.38
32k no 1.93 1.81 0.94 1.97 0.93
yes 2.16 1.42 0.91 0.79 0.42
64k no 1.86 0.89 2.96 1.01 1.27
yes 0.82 1.96 0.96 0.71 .
128k no 0.89 1.09 1.06 3.30 1.23
yes 1.22 0.99 0.38 0.40 .