I have a Mac Classic II and would like to add a second
internal HD.
The internal SCSI cable only has one plug, but if i were
to buy one with two would I be able to connect both?
Or would it be possible to connect the internal drive to
the external DB-25 SCSI connector somehow?

thanks,
--Ian

gbtmud2[at]hotmail.com (Ian Gowen) writes:
>
> I have a Mac Classic II and would like to add a second internal HD.
> The internal SCSI cable only has one plug, but if i were to buy one
> with two would I be able to connect both?

This should work, but there may be a few gotchas:

1: Termination. Make sure that the drive at the end of the cable is
the only one with termination turned on. There may be some issues
involving termination on the motherboard as well, but I couldn't
say for sure without actually seeing the computer up close.

2: Airflow. Use the shortest cable you can that has the required
connectors. Extra cabling obstructs airflow and may cause
overheating.

3: Power supply. I don't know if the Classic II's PS has enough
watts to power two hard drives. If it doesn't, you'll get flaky
and unstable behavior.

> Or would it be possible to connect the internal drive to the
> external DB-25 SCSI connector somehow?

No. Although it's theoretically possible, I really don't think you
want to try this.

-- David

shamino[at]techie.com (David C.) wrote in message news:<m2ad874rsd.fsf[at]qqqq.invalid>...


> 3: Power supply. I don't know if the Classic II's PS has enough
> watts to power two hard drives. If it doesn't, you'll get flaky
> and unstable behavior.
>

Hmmm. hadn't thought about that. Internally there's only one power
connector, but I might try a y-adapter; the connector is the same
as any PC power connector.

> > Or would it be possible to connect the internal drive to the
> > external DB-25 SCSI connector somehow?
>
> No. Although it's theoretically possible, I really don't think you
> want to try this.

why not? ;)

-Ian

Ian Gowen writes:
> David C. wrote:
>>
>> 3: Power supply. I don't know if the Classic II's PS has enough
>> watts to power two hard drives. If it doesn't, you'll get flaky
>> and unstable behavior.
>
> Hmmm. hadn't thought about that. Internally there's only one power
> connector, but I might try a y-adapter; the connector is the same as
> any PC power connector.

Getting an extra connector is easy.

But if the power supply doesn't provide enough power for two drives,
you're SOL.

On the plus side, older drives consumed a lot more power than modern
drives. If you're replacing the original drive with two modern ones,
you might not exceed the system's power budget. If you're leaving
the original drive in place, and simply adding a second, it's
anybody's guess.

One useful thing here is the jumper that most SCSI drives have for
sequential spin-up. When this is set, the drive motor won't spin up
when it's powered on, but will wait for a varying amount of time,
based on the SCSI ID. (e.g. ID 0 spins up immediately, ID 1 after 30
seconds, ID 2 after 1 minute, up to ID 6 spinning up after 3
minutes.) This feature prevents all the drives from trying to spin
up at once, which may create a momentary power drain that's too large
for the PS to provide.

Not all drives have jumpers for this, but many do.

>>> Or would it be possible to connect the internal drive to the
>>> external DB-25 SCSI connector somehow?
>>
>> Nqo. Although it's theoretically possible, I really don't think you
>> want to try this.
>
> why not? ;)

Well, for one thing, it's ugly. To have a cable attached to a rear
port, going back inside the case makes the entire system look like a
hacked-up mess.

Also, the 25-pin connector doesn't have the extra 25 ground wires
that the internal 50-pin ribbon has. Although most drives seem to
work OK with this connector, it's still a bad thing. This connector
has never conformed to any version of the SCSI spec.

If you're attaching an external SCSI drive to a legacy Mac, then you
have no choice but to use it. To use it for an internal drive when
you've got a perfectly good internal 50-pin bus, however, is just
plain dumb, IMO.

-- David

On 10/11/03 12:18 PM, in article m2ad874rsd.fsf[at]qqqq.invalid, "David C."
<shamino[at]techie.com> wrote:

> gbtmud2[at]hotmail.com (Ian Gowen) writes:
>>
>> I have a Mac Classic II and would like to add a second internal HD.
>> The internal SCSI cable only has one plug, but if i were to buy one
>> with two would I be able to connect both?
>
> This should work, but there may be a few gotchas:
>
> 1: Termination. Make sure that the drive at the end of the cable is
> the only one with termination turned on. There may be some issues
> involving termination on the motherboard as well, but I couldn't
> say for sure without actually seeing the computer up close.
>
> 2: Airflow. Use the shortest cable you can that has the required
> connectors. Extra cabling obstructs airflow and may cause
> overheating.
>
> 3: Power supply. I don't know if the Classic II's PS has enough
> watts to power two hard drives. If it doesn't, you'll get flaky
> and unstable behavior.
>
>> Or would it be possible to connect the internal drive to the
>> external DB-25 SCSI connector somehow?
>
> No. Although it's theoretically possible, I really don't think you
> want to try this.
>
> -- David

These were not really set up to have two internal drives, though you might
get away with it using a longer SCSI cable. I don't recommend it; an
external drive is simpler.

Brian

Brian Paul Ehni <behni[at]comcast.net> wrote in message news:<BBAF7D92.48A73%behni[at]comcast.net>...
> These were not really set up to have two internal drives, though you might
> get away with it using a longer SCSI cable. I don't recommend it; an
> external drive is simpler.

Yes, but also more expensive :P

--Ian

Brian Paul Ehni <behni[at]comcast.net> writes:
>
> These were not really set up to have two internal drives, though you
> might get away with it using a longer SCSI cable. I don't recommend
> it; an external drive is simpler.

The only technical reasons why two drives might be a problem are the
ones I mentioned (termination, cooling and power supply).

As far as the SCSI data bus is concerned, there is absolutely no
difference between the internal and external connectors.

The Classic II does not have two SCSI busses. The 25 pins of the
external connector are wired straight to the 25 non-ground wires of
the internal connector.

-- David

shamino[at]techie.com (David C.) wrote in message news:<m2y8vopomx.fsf[at]qqqq.invalid>...
> The only technical reasons why two drives might be a problem are the
> ones I mentioned (termination, cooling and power supply).
>
> As far as the SCSI data bus is concerned, there is absolutely no
> difference between the internal and external connectors.
>
> The Classic II does not have two SCSI busses. The 25 pins of the
> external connector are wired straight to the 25 non-ground wires of
> the internal connector.
>
> -- David

yeah, I probably wasn't clear before; i didn't want to connect the
drive internally and use the external port, i wanted to use the internal
drive externally.

Basically what I'm trying to do is install the Debian GNU/Linux m68k
version on this thing, for fun, but I don't want to destroy the Mac
drive because I still use MacOS for all those awesome games ;)

So since the Debian Mac boot loader is a bootstrap, having two hard
drives should make it a whole lot easier.

--Ian

Ian Gowen writes:
>
> yeah, I probably wasn't clear before; i didn't want to connect the
> drive internally and use the external port, i wanted to use the
> internal drive externally.

Oh. That's completely different. There's no problem with that.

External SCSI cases are easily available. New ones can be a bit
pricey, but you can get used ones at computer shows and eBay without
any problem.

Any narrow (50-pin, not 68-pin wide) case with a large enough power
supply (25-35W should be plenty for a single hard drive), a cooling
fan should do it.

Most SCSI cases have wires to connect the drive's SCSI-ID jumpers to a
selector on the back of the case. If yours doesn't or if you can't
attach it to your drive, don't worry. It just means you'll have to
set the ID on the drive itself, where it will be inconvenient to
change later on. Pick any SCSI ID that doesn't conflict with other
devices (the Mac itself should be 7, and the factory-installed drive
should be 0.)

When you do this, make sure termination is disabled on the drive and
use an external terminator (either attached to the case's passthru
port or built-in to the case.)

If you don't leave any drive internally, you may have to terminate
the SCSI bus on the motherboard. I don't know if a Classic supports
this (if it does, it will be either via DIP switches, jumpers, or
resistor packs near the internal SCSI connector.) If there's no way
to do this, you may need to do it externally using a passthru
terminator on the cable between the Mac and the first external SCSI
device.

If you're going to leave the internal drive in place, then ignore the
previous paragraph.

> Basically what I'm trying to do is install the Debian GNU/Linux m68k
> version on this thing, for fun, but I don't want to destroy the Mac
> drive because I still use MacOS for all those awesome games ;)

Sounds like a plan.

-- David

shamino[at]techie.com (David C.) wrote in message news:<m2llrkwm7d.fsf[at]qqqq.invalid>...
> > Basically what I'm trying to do is install the Debian GNU/Linux m68k
> > version on this thing, for fun, but I don't want to destroy the Mac
> > drive because I still use MacOS for all those awesome games ;)
>
> Sounds like a plan.
>
> -- David

yep. Before I even read your message I picked up an external enclosure
at the local goodwill for $5. Not bad. It's old, but it works.

Thanks for all your help.

--Ian