Re: [TUHS] /dev/drum

On 2018-04-28 02:19, Noel Chiappa wrote: Gah. If I were to try and collect every copy made, it would be quite a collection. Thanks for the offer. If you really want to get rid of one, and is willing to send to Switzerland, then I'll take it in a private mail. But you don't really have to. Cool. Thanks. That is a very different terminology. The MMU is not even called the MMU, but the "Memory Segmentation Unit". Very interesting. So there was a total change in terminology early in the 11/45 life, it would appear. I wonder why. I can only speculate, but I probably would not blame some market droids. Trying to think about this, I feel that one of the most important differences between segmentation and pages are that with segmentation you only have one contiguous range of memory, described by a base and a length register. This will be a contiguous range of memory both in virtual memory, and in physical memory. With segmentation you cannot have your virtual memory split up and spread out over physical memory. You can also, pretty much, arbitrarily point where in physical memory your virtual memory starts and ends. With pages, this is obviously not the case anymore. The PDP-11 do have the ability to have pages start at close to arbitrary addresses in physical memory, but you can certainly have your virtual memory spread out over different places in physical memory. Your virtual memory is also not just described by a base and length, as you have 8 pages, starting at fixed virtual memory addresses. You can also have "holes" in your memory, with pages that are invalid, yet have pages higher up in your virtual memory which are valid. Something that is impossible with segmentation, since you only have one set of registers for each memory type (at most) in a segmented memory implementation. I mean, when people talk about segmented memory, what most everyone today thinks of is the x86 model, where all of this certainly is true. So, by this definition, it would be very wrong to call what the PDP-11 have segmentation. And I would suspect that to be the reason why DEC changed their terminology. Segmentation simply started to become an established term, and it did not match what the PDP-11 did, so the documentation had to change to better describe what it was. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt(a)softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol