On Tue, 29 Jan 2002 [EMAIL PROTECTED] wrote: > As far as I remember from reading the Lyons' book, there were > 16 mapping descriptors for text and data each. I think, 1/16 > of the address space is not too big, and in absolute values > it's the size of today's pages (4KB).
well I had dropped this thread as I figured the list would not want to hear it, but yes you're right. The KT-11 MMU worked this way. I still have my manuals, as it was a pretty interesting piece of hardware. Unix was the first OS to actually use the split I/D capability, so while the various DEC OSes were stuck at 64K Unix programs could run at 64kI/64kD. Also user mode/super mode/kernel mode each got its own set. There was also a weird instruction called MFPU (move from previous user space) that allowed "bcopy shared memory"-type programming. Once again Unix actually used this, the DEC OSes did not, so Unix was the first to find the bugs in this hardware too. Once university as I recall actually added the wire to its machine to make MFPU work correctly ... The kinds of things you had to do in Unix on an 18-bit-physical address space machine with 16-bit addressing bear interesting similarities to what we have to do now on 36-bit mode Pentiums with 32-bit addresses. What goes around comes around ... ron To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
