basically the "BUNCH" companies used just about everything in those days. hey the B1700 was bit addressable and switches microcode depending on the language so the MMU's were all over the place you are right the MMU in the 11 was in today's terms strange but so were many others in those days. find an old copy of the early 1970's classic Bell, Grason, and Newell's. "computer structures: readings and examples". if you wAnt to learn more about those contemporaries most of the papers describing those systems are in it. Dan Seworiok updated it in the late 1970's and swapped in some then more modern systems On Dec 18, 2012, at 1:12 PM, <Paul_Koning at Dell.com> wrote: 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