Large SMP/UP Performance Deltas

We're currently in the processes of benchmarking SMP performance, against UP performance for our applications and have hit a wall in terms of performance. (Boxes being tested are an 8-way R/S 6000 and a 59H - fast UP). Problem is our application runs an order of magnitude slower (25 minutes vs 2 minutes) on the SMP box. What I need help understanding is an alarmingly high number of bufreads on the SMP box (10 million vs 1 million on the UP) running the same application on a database that was "onunloaded" from the UP to the SMP. Interesting tidbits: UP - AIX 3.2.5 / Informix 7.10.UC1 SMP - AIX 4.1.4 / Informix 7.12.UC1 Disks are identical, SMP has 3x real memory, and both databases are fragmented by expression. Indexes verified with oncheck Application is single threaded and one copy is running. My current tongue-in-cheek explanation is 8processors = 8times the number of reads :-}, however I'm looking for another theory. TIA Craig Hollenbaugh csh@kru.com DBA never wanna be