On Friday, April 23, 2004, at 01:40 PM, Jeff Walther wrote:
The Q900 (I think) and Q950 (definitely) were the first machines to have dual busses on the motherboard, but there was a hitch. There are two 53C96 SCSI controller chips on the motherboard, so there are two electrically seperate SCSI busses each with its own requirements for termination and each separate and independent from the other SCSI bus.
But the two busses are treated as one bus logically, meaning that you can't duplicate SCSI ID's between the two busses and so are limited to a total of 7 SCSI devices instead of the 14 you would expect. That is the software and ROM of the Q9x0 thinks that there is only one SCSI bus there. SCSI Manager 4.3 added support for multiple SCSI busses.
If you load SCSI Manager 4.3 or one of the later OSs which have it built in, then the two busses are (may be?) treated as separate logical busses and the full complement of 14 drives is supported with the additional exception that at boot time, any drive you are booting from or otherwise need access to before the OS loads needs to have a unique SCSI ID amongst both busses. This is because this old machine does not have SCSI Manager 4.3 support in the ROM and so the two physical busses/one logical bus limitation holds until the OS has managed to load a copy of SM4.3 and everything that happens before that needs to follow the old rules that applied when the Q9x0 shipped.
An interesting experiment here is to install a JackHammer SCSI card in the Q9x0. Reputedly, the JackHammer has SM4.3 in its on board ROM and so the question is whether having the Jackhammer present will lend support for both built-in SCSI busses before the OS loads.
Jeff,
This is what I'm trying to do! I have a beautiful 950 (at least to my eyes YMMV :-) I have installed the "five drive carrier" and a CDROM. The CDROM hangs off the internal bus 0. Then I have a JackHammer card installed with five Seagate ST15150W drives (well they are actually COMPAQ OEM - bought a box off eBay). I have a nice 68pin cable with a built on terminator.
I have been using FWB HDTK (Version 3.something) to format and setup the drives. I can get all 5 drives to work as single drives, and with OS 8.1 installed on one, the machine will boot. For some reason, in this mode, it will not boot from the CDROM. Is this because one of the drives on the JackHammer is ID 3 as is the CDROM?
My real disappointment is that I had intended to create a RAID array by striping the disks, but if I do this, and install OS8.1 on the stripe, the machine just will NOT re-boot :-(
Any suggestions?
John
-- Vintage Macs is sponsored by <http://lowendmac.com/> and...
Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! |
Support Low End Mac <http://lowendmac.com/lists/support.html>
Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/vintage.macs%40mail.maclaunch.com/>
Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
