On Dec 18, 2012, at 1:05 PM, Clem Cole wrote: Paul. given the time (late 1960's/early 70's) the prevailing page sizes were 64 / 128 / 256 / 512 bytes which just happen to map to the sizes of blocks used in disk controllers. 1/4/8 k pages were a few years in the future. 512 bytes, sure. I'm wondering about other sector sizes. RC11 had 64 byte sectors, RF11 2 byte "sectors". I don't remember any other sector sizes on DEC gear. CDC 6000 series had 322 12-bit word sectors. IBM 360 series used whatever sector size you wanted, varying from sector to sector if you were so inclined. The PDP11 MMU is an odd beast -- physical start on 64 byte granularity, page size variable between 64 bytes and 8192 bytes, but virtual base addresses only multiples of 8192 bytes. paul