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Aucbvax.2945 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Fri Sep 4 14:24:59 1981 [Jcp: Re: [decvax!pur-ee!p: UNIBUS problems on new processors]] >From mike.bmd70@BRL Fri Sep 4 14:14:05 1981

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Date: 4 Sep 81 14:44:42-EDT (Fri) From: Jcp at bmd70 To: Michael Muuss <MIKE@BMD70> Subject: Re: [decvax!pur-ee!p: UNIBUS problems on new processors]

Mike:

From the drawings I have seen, (and the 11/24 I have seen), the UNIBUS on both 11/24's and 11/44's goes thru a PAX (Program Address Extension) Module if you are using more than 128Kw of memory. This produces similar problems as the UNIBUS MAP on an 11/70, and the other extended memory processors. In additon, on the 11/24, memory managment is done by a VLSI chip, which incurs additional delay.

On an 11/70, the KT (mem. manager) introduces ~90nsec of delay and the UNIBUS MAP is good for another 90.

My impression is that on the 11/24, the KT is good for ~100nsec and the UNIBUS MAP for another ~100nsec, making the 11/24 UNIBUS good for a little less than 1Mhz. (11/70 is 1Mhz).

Incidentally, the same is true for an 11/23 (Qbus), except that there is no PAX for the 11/23, yet. (Yes, DEC is planning to introduce one...)

You may want to relay this info.

-JCP-

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