Several days back, I posted a comment/question from Kazushige Goto (the developer and maintainer of Goto BLAS) - "By the way, please ask your R developer to rewrite memory allocation function including garbage collection. They give 4 byte offset memory region and never perform well (or it will cause segmentation fault. 4 byte offset is fatal). Since R use complex double precision, memory alignment should be at least 16 bytes..." Goto obviously has thought an awful lot about such things, and (apparently) wrt to R (and he is extremely well-known in programming circles - you don't write a BLAS unless you know a thing or two). Since a number of R users (like me) make use of Goto BLAS, I'd hope that on the devel group could comment/reply. I'll forward to Goto.