On Mon, Jul 8, 2019 at 1:30 PM Noel Chiappa via cctalk < [email protected]> 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
