I will greatly appreciate help in understanding the puzzling wild variation in the execution time of small test/benchmark program, as explained below. (1) The nature of the benchmark/test program: A floating point arithmetic intensive atmospheric chemistry modeling task. It used to take, in a consistent manner, around 2m 37s on my machine when it was running under SuSe 9.1 Pro. When I run the benchmark program, I shut-off all other programs. Thus, during its run, it is the only active program. THe rest are belonging to root are sleeping. There is no other user. (2) The machine: Dual Opteron 250 with 4 GB of PC3200 (DDR) memory in 4 dimms that fill two dimms on cpu0 and two dimms on cpu1 installed in Tyan Thunder K8 system board that has American MegaTrend AMIBIOS V2-04. It now runs under SuSE 9.3 Pro and the Linux version 2.6.11.4-21.7-smp (geeko@buildhost) (gcc version 3.3.5 20050117 (prerelease) (SUSE Linux)) #1 SMP Thu Jun 2 14:23:14 UTC 2005 (3) Background of the problem: After only 4 months of the delivery of the machine by the vendor, the mother board failed. The machine was sent to the vendor. He then replaced the mother board with a new one and installed SuSE 9.3 Pro to bring the machine up-to-date with the Linux version 2.6.11.4-21.7-smp (geeko@buildhost) (gcc version 3.3.5 20050117 (prerelease) (SUSE Linux)) #1 SMP Thu Jun 2 14:23:14 UTC 2005 (4) The problem: After the repair and upgrade to 9.3 Pro, the execution times of the same test/benchmark program varies widely between run to run. It is never consistent. It varies from 2m 37s to more than 6m. A pattern is seen in the variation. Usually, the longest execution time is when the machine is started after remaining shut-off for a few hours. The shortest execution time is obtained after the machine has been constantly on for abot 7 to 10 hours. (5) My puzzle: While a computer is well known to be reproducible, the wild variation by a factor of almost 3 in the execution is very disturbing. What could be the cause? Does it mean that some vital component involved in execution of the numerical modeling (RAM memory or the memory on the CPUs) are loose or erratic and may be about to go bad? I am just puzzled. Any clue from you all will be really very very much appreciated. -- Best regards. Sheo (Sheo S. Prasad) Creative Research Enterprises 6354 Camino del Lago Pleasanton, CA 94566, USA Voice Phone: (+1) 925 426-9341 Fax Phone: (+1) 925 426-9417 e-mail: ssp@CreativeResearch.org