[Jcp: Re: [decvax!pur-ee!p: UNIBUS problems on new processors]]
utzoo!decvax!ucbvax!unix-wizards
utzoo!decvax!ucbvax!unix-wizards
Fri Sep 4 14:24:59 AEST 1981
>From mike.bmd70 at BRL Fri Sep 4 14:14:05 1981
----- Forwarded message # 1:
Date: 4 Sep 81 14:44:42-EDT (Fri)
From: Jcp at bmd70
To: Michael Muuss <mike at 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-
----- End of forwarded messages
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