> SCSI chains devices and a termination must be done on two
> ends. [...]
True, but a typical SCSI adapter card will handle its end
without your doing anything. For a less typical example
card, the KZPBA-CB/CY is the (HV) differential version of the
QLogic card, and it has a bank of socketed SIP resistor packs
for termination (near the external 68-pin connector). If
those are removed, then you can put that card into the middle
of the (HVD) SCSI bus. (Many very old SE disk drives also
had places for termination resistor packs, to be installed in
the last drive at the end of the cable.) Nowadays, a cable
might come with a terminator at one end, or a box (like the
Sun 611) might include an automatic terminator, or you might
need to use an explicit terminator.
With the single-ended KZPBA-CA/CX card, the termination at
the card is either automatic or permanent, so you don't
need/want any other terminator at that end of the cable.
> Termination can be active or passive.
True.
> Passive adapters are used to cap the end of the chain
> where you need it to terminate due to BIOS/SRM
> considerations.
Termination is needed at both ends of the bus for
electrical signal integrity (to stop reflections). Active
terminators do a better job at higher speeds. For a KZPBA,
you probably don't care. Any UltraXXX terminator is probably
active. Older stuff might be passive.
> In the case with DEC tech, it must be LVD or something will
> go up in smoke.
No. Old single-ended stuff is ok. Just avoid the old
(high-voltage) differential stuff (like a KZPBA-CB/CY card or
Seagate drives with model numbers ending in "D" (typically
"WD")). Modern stuff is typically SE/LVD, so it'll
automatically use (faster) LVD signaling unless it sees the
higher voltages associated with an old SE device on the bus
somewhere. With a KZPBA-CA/CX card, everything will be in SE
mode, not LVD (Ultra).
> 15K's are not ideal due to heat generation, though
> certainly better than the original 10k's.
Perhaps. Actual power specs are more reliable than any
generalization.
> U320 is backwards compatible with U160 and in either case the
> cards (Internal or External) available on the XP1000 operate
> at U160 spec. (~40mb/s)
Among SE/LVD devices, everything's compatible with
everything. The slowest device on the bus limits the speed
for everyone. (Which is another reason to keep an old SE
tape drive away from a bus full of faster LVD disks.)
I know nothing, but I'd guess that "Ultra160" is _not_
called "Ultra160" because its speed is 40M<anythings>/s.
I typically see lower bus speeds when I connect an
external Sun 611 box to an existing internal bus. I know not
whether that's caused by the additional cable length or the
box's automatic terminator, or what.
> The AlphaStation XP1000 supports 4 x (3.5" x 1") internal
> SCSI Disks (2x 3.5", 2x in 5 1/4" bay), [...]
The "XP1000 System Reference and Maintenance Guide" (cited
earlier) has the actual facts (which differ from this
description):
file:///XP1000%20Service%20Guide/service/co_bays.htm
It also says:
Note: Some large hard disk drives generate enough heat
during normal operation to require a twin fan module to be
installed in conjunction with them. Use the top
front-accessible drive bay for such drives and their twin fan
modules.
I've never seen this "twin fan module".
> This begs the question since the modern and more plentiful
> disks available are 80-pin, I have mostly if not always found
> only 68-pin cables/ribbons, so would you need a 68->80
> adapter for each node of the SCSI chain?
Yes. As before:
> > I found they are 80-pin and I only have the older built-in
> > 68-pin to start with. So what does that mean?
>
> That means that you'd need an 80-to-68-pin adapter to use
> one.
> I saw Steven's post about his own (internal) stuff and he
> uses 68-pin ribbons with both of the links he posted, yet he
> also says that he uses 80-pin (More modern) SCSI disks with a
> similar setup.
Yes, with a 80-to-68-pin adapter on each disk. As claimed
here earlier, $5 or less should get you a nice one.