🚀 go-pugleaf

In article <DCppwC.nB5@wombat.hanse.de>, root@wombat.hanse.de (Bernd "Bernie" Meyer) writes:
> medcalf@ppc5.svo.dfw.ibm.com (Jeff Medcalf (214) 280-5970 IBM SDO) writes:
> The point of the post by Frere was that he could take his disk and walk over
> to any other Mac and just plug it in, and have it show up on the desktop. 
> To which someone (I think not me) responded that this works as well with 
> SCSI equpipped PCs. I don't think not booting from an SCSI device would be a
> big problem in this regard. Booting, also, isn't an "SCSI function". If
> there is nothing else to boot from, that would be a pretty strange PC,
> right? If there _is_ something else, no magic by the SCSI host controller
> can override that WD-compatible boot. So the PC can obviously boot from
> something, and adding an SCSI device won't take that ability away, right?

It is not always as simple on the PC as just plugging in a drive and it works.
For example, if there is no extended mode SCSI driver loaded, and drive IDs
0 and 1 are already in use, then drive 2 won't show up.  This does not happen
on the Mac, ever.

If the machine's internal SCSI drive is dead, it is useful to boot from an
external SCSI drive that contains recovery utilities and attempt to recover
the drive.  On the Mac you can do this.  On the PC you cannot.

> Have you _really_ seen an SCSI card that wouldn't coexist with an IDE card?
> I doubt that, really.

Yes, I really have.  Both cards mandated that they be the boot device.
Neither allowed that capability to be shut off.  The other effect of this
is that two of that type of SCSI card could not be put in the same PC.

> Then that is not an SCSI equipped PC, but a PC with a proprietary scanner on
> a proprietary interface, which somehow resembles SCSI. My Mitsumi interface
> looks a lot like IDE, too, but still I can't connect a harddisk to it.

It was advertised as SCSI.  That doesn't make it so, but that's how it
was advertised.

> Exactly. DOS has no concept of more than two harddisks (there is no 2
> devices limit on any card I know, but a two harddisks one). So how would you
> expect the SCSI card to overcome this? Run something which has a decent set
> of drivers, and you are fine. I am really sick of everybody equating
> PC=DOS+WINDOWS

Exactly my point.  This does not happen on the Mac.

> Still, an "SCSI equipped PC" will probably not get into serious trouble when
> you add another device to the SCSI bus just because the SCSI controller
> supports only one IRQ, right? If you want to talk about getting to the point
> of having an "SCSI equipped PC", we might share some bad experiences. But
> then, getting a Mac might be a bad experience as well :-)

True.  But you first have to get the SCSI card installed.  And no, getting
a Mac is not a bad experience. :-)

> An SCSI drive doesn't have heads, cylinders and sectors (BTW: Show me a
> drive with more than 1024 sectors per track, and I'll be impressed. I think
> they are currently at around 100 sectors/track, with many many tracks). An
> SCSI disk device is a collection of consecutive blocks, numbered from 0 to
> N-1. 

Ummm...a SCSI drive *does* have those parameters.  That you do not enter
them into the CMOS does not make them go away!  That's not a "fake...for DOS."

> Nonsense. Booting is a thing that happens _before_ the OS runs. And after
> the OS runs, disks are only handled through symbolic names (or table
> entries, BIOS calls, or whatever), not through IDs. Every host adaptor that
> will find a disk at ID 4 at all will also give you access to it in DOS and
> Windows.

Install DOS on a hard drive.  Set the drive to ID 4, and then reboot.  DOS
will not boot.

> We needn't argue that there is a lot of crap out for PCs, and that
> especially the combination of second-thought addition SCSI and
> not-a-single-thought DOS is problematiic to get to work. But I strongly
> disagree with your statement that, once you have managed to do that, simply
> plugging in another device will potentially get you into a lot of trouble.

Necessarily, no.  Potentially, yes.

-- 
+-------------+-------------------------------+--------------------------+
|Jeff Medcalf | medcalf@interlock.dfw.ibm.com |                          |
|CTG-Dallas   | JKMedcalf@aol.com             | Power Series support     |
+-------------+-------------------------------+ SVMP/Tech Eval           |
|I not only don't speak for IBM,              | Comm Mgr/2               |
|I don't even *know* who speaks for IBM!      |                          |
+---------------------------------------------+--------------------------+