8 Jul
2019
8 Jul
'19
4:36 p.m.
On Mon, Jul 8, 2019 at 1:30 PM Noel Chiappa via cctalk <
cctalk at classiccmp.org> wrote:
So early KL10's (KL10-A's, to be precise) only
support a single DTE20, and
no RH20's. Later ones supported up to 4 of the former, and up to 8 of the
latter.
That's because the 1080 has different I/O backplanes than the
1090/1091/1095/2040/2050/2060.
The 1080 was intended to replace a KA10 or KI10, so it would be used with
external memory and external channels. It only needed a single DTE20 for
the internal console PDP-11, and it didn't need an RH20 because the disk
would be attached via an RH10 on the external I/O bus and external memory
bus.
I always supposed this to be part and parcel of the 'Model A/Model B' CPU
difference, but no... EK-0KL10-02 Part 1 (no title,
seems to be notes for
F/S) pg. 9, says both KL10-A and KL10-B's are PA (DEC jargon for the Model
A CPU - below), but the former has no RH20's, the latter does.
The -PA and -PV designations (and much later -PW for -1095 and -2065) are
for the "arithmetic processor" (APR), which is the main CPU portion of the
KL10. That's independent of the number of DTE and RH20 slots, though AFAIK
DEC never sold a configuration with a -PV CPU and the small I/O backplane.
(A note at the bottom of the page says that a PA is a 'Model A', and
describes it as having "internal channels". The PV is a 'Model B' -
extended addressing, larger ucode, faster clock.)
A system with a -PA APR could have internal RH20 channels or not, and it
could have cache or not, depending on the system configuration
For example:
* DECsystem-1080: cache, external memory bus adapter (DMA20), and external
I/O bus adapter (DIA20), but no internal channels
* DECSYSTEM-2040: internal channels (usually two) but no cache or external
memory bus adapter.
So my new theory is that it's the MBox (either the backplane, the boards,
or the wiring from it to connectors, etc) that is the
difference between
the KL10-A and the KL10-B.
It's not just the MBOX; there are significant EBOX differences as well.
Various modules from the entire CPU are different, and the backplane wiring
is slightly different. It was possible to upgrade a -PA to -PV by swapping
modules and adding some wraps to the backplane, but if you had the small
I/O backplane, upgrading to -PV didn't make it possible to add any more
channels or DTE20s.
Part of the motivation for upgrading a -PA to -PV, even if you weren't
planning to use extended addressing, is that the -PV is faster than the -PA.
Eric