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Quadra 950: SCSI Storage, Partitioning and Boot Disks

The Quadra 950 has two SCSI buses. I therefore originally thought that this meant 12 devices (the logic board takes ID 7 on each bus.) Turns out I was wrong... the OS only supports a maximum of 7 devices in total! This is achieved by a software bridge that logically joins both buses. Therefore, you cannot have devices with the same SCSI ID on both the internal and external buses! How frustrating.

Low End Mac explains it, relating to System 7:

Although there are two separate SCSI buses, System 7.0-7.1 "folds" them together so the operating system sees a single virtual SCSI bus. Thus, under System 7.0-7.1 (and only under those systems) you must make sure that all devices on both chains have unique IDs.

So, what's the plan? Fill the bus! 7 slots. That's 2 CD drives, 4 hard disks and a ... maybe I'll try and find a zip drive... with the case full it will have to be external.

Setting SCSI IDs

This seems to get a few people confused. Each SCSI bus (of this vintage) has a maximum of 8 devices. These come with the IDs of 0 through to 7. To represent this, a value comprising of 3 bits is used. If you know your binary math, then this is obvious, if not, then please look at the table below. The bits relate the the jumpers seen on all SCSI devices of this vintage.

Listed below is the Jumper and it's corresponding decimal value in parenthesis. Summing the values associated with the bridged jumpers gives you the SCSI ID.

Jumper Values
SCSI ID J0 1 J1 2 J2 4
0 OFF OFF OFF
1 ON OFF OFF
2 OFF ON OFF
3 ON ON OFF
4 OFF OFF ON
5 ON OFF ON
6 OFF ON ON
7 ON ON ON

So, from above, the jumpers indicate the values 1,2 and 4. i.e. a jumper bridging 'Jumper 0' will give a value of one. When you bridge multiple jumpers then you sum the values.
(i.e. J1 + J2 = 2 + 6 = 6 or J0 + J2 = 1 + 4 = 5 and so on.)

With this knowledge, you can now configure all of your old SCSI devices to play happily on your bus(es). On the Quadra I had all of the HDDs and the internal CD drive on one bus. I used 0 for the boot HDD, 1 for the CDROM and then 2,3,4 for the other disks.

Externally I had the Apple PowerCD plugged in and configured to SCSI ID 5. Just to re-iterate, the external devices, although on a separate physical bus, join the internal single bus and therefore must be using unique IDs. They cannot re-use the IDs of internal devices!

Make sure that your external SCSI devices have unique IDs. They cannot use the same IDs as internal devices!

Terminating SCSI Buses

The SCSI bus is a long chain of devices. Communication along the chain is terminated by a set of resistors and/or current. Some SCSI devices provide internal termination facilities. If you enable termination on a device, then you should not put any other SCSI devices further along the chain. In the end, the chain should look like a row of christmas lights. One end is the motherboard, and this is terminated internally. The other end is a terminator on the cable, or a device with internal termination. ALL devices in the middle must then be non-terminated!

Macintosh SCSI Hardware Issues indicates that no drives in the Quadra 900/950 need be terminated. Instead the cable should have termination at the very end. An active terminator is recommended over a passive one. This identifies with the SCSI bus requirements above. All devices between the terminators (logic board and final terminator) must be non-terminated. The only exception to this is when the final device has internal termination.

SCSI Converters

The Quadra 950 only has 50-pin internal sockets for SCSI cables. It runs an NCR 53C96 SCSI Controller with a theoretical speed limit of 6 MB/s. Finding 50-pin SCSI devices nowadays is a real pain and most now have the vintage "price tag" on them. Fortunately, there's no need to worry. The SCSI interface happens to be backwards compatible and, although there are several different types of connectors, most can be converted (or downgraded!) to the lowest standard.

In our case we need all our devices on the flat 50-pin IDC internal ribbon cable standard. Scouring the net (and then eBay), resulted in some easy finds. A Hong Kong seller (zero results from Australia, as per usual) had the converters for AUD$9.50 a pop. These convert 50/68-pin to SCA 80-pin drives. And I had to buy these after-the-fact as I'd already purchased ~100gb SCSI drives with these plugs. I'd bought the drives because they said 'vintage'... just not 'vintage' enough for the Macintosh.

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The SCA interface includes automatic ID selection and optional termination. This gets converted in the adapter. There are jumpers there for the ID (as per the table able) and then a TE jumper with enables internal termination. This means that I can have any of these devices on the end of my chain when the TE jumper is bridged.

Installing 80-pin SCA drives into the Quadra 950

The size of the case would make one think that you'd be able to store around 8-10 drives comfortably. You would be able to... if the designers had provided the slots. Instead, there are only two fixed locations to install drives. One of these gets stolen by the internal CD-ROM if you choose to mount it. I was hoping that, as that the bays are removable, someone had come up with a readily-available solution for more drive mounting. This forum post was all I could find; the user has managed to get 8 drives in the Quadra. Unfortunately all the images are gone...

I used my second (new) SCSI cable and plugged it into the socket under the power supply. This is the second SCSI bus; it's the internal side of the external bus. I even managed to sneak the cable up behind the power supply. Let's hope it doesn't get too hot!

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First things first... DO NOT sit drives on top of each other freely and turn the power on. Anything could be shorting between them and cause issues. I powered the drives via the piggyback to my new fan and it cooked the lead!

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First attempts to get the devices to show failed miserably. The cooking of the lead may have cooked the converters, but there's no 'smarts' to them, so I don't see how that could have happened. I put the two new HDDs as IDs 3 and 4 on one bus, also testing on the other, but never once did a drive show up in any scanning application. One drive showed a little flickery HDD activity once, but most of the time they both just lay there, like stunned mullets.

Reading SCSI Notes for 68k Macs, the quote that got me was:

80-pin drives aren't required to be 68-pin SCSI, IIRC, so a rare SCA drive that doesn't support Wide might exist. All the same cautions apply to attaching an SCA drive to a 50-pin bus as attaching a 68-pin drive, except that it's even more common for cheap adaptors to cause heartache to those trying to save money.

Go ahead and put those SCA drives into your 68k, but make sure you've got a fair bit of time laid out for getting them up and running. Hopefully it'll just work out fine, but you might have to debug something, possibly including replacing some of your adaptors if they're not working well.

Nothing is working well... the adapters are crap... the drives are crap? I don't know... but I'm writing all components off at this point. Might try again tomorrow.

...next day...
Holy shit. I just booted today after all the unsuccessful attempts last night. The power splitter cable melted when I turned the power on! DO NOT ... EVER ... use SCA drives in your Quadra 950.

...I'll be back once I purchase expensive 50/68-pin HDDs... I AM NOT touching these SCAs anymore.
(Tell me if anyone has ever successfully used an SCA drive in their Quadra 950... kthx.)

Installing 68-pin drives into the Quadra 950

These have both arrived (9g and 36g) and they both just work! ID set, converter in place and presto, the drives appear and are completely functional. Onto the partitioning!

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There are at least two sorts of adapters... the above shows the 'inline' version, a single moulded unit. There's also the version with a PCB in-between. Both adapters worked perfectly for me.

Partitioning Disks

I expected there to be partition size limits, but that doesn't seem to be the case with MacOS 8.1 and higher. There's a multitude of tools available, so I've chosen to try and few of them out below. If you need to download any then check out Gamba's page.

Apple HD SC Setup (Patched)

When Apple HD SC Setup opens, you'll be presented with an ugly little dialog. I suppose it's the visual representation of that similarly ugly little tool called fdisk. Keep mashing the Drive button until the text above it matches the drive you want to work with. In this case mine was SCSI ID 4.

There's notes here on how to set up partitions via Apple HD SC Setup. Note that you have to 'Initialize' a disk before you can manage partitions! If initialisation is formatting, then wouldn't you have thought that it would want to set up partitions first? It seems that this isn't the case. Initialisation also takes a REALLY long time; it'll create and format an initial 4.1gb partition for you.

apple-hd-sc-setup-3 apple-hd-sc-setup-1 apple-hd-sc-setup-2

Once you have the option to press the Partition button, do so. You will be presented with a window that'll let you format your current partition. We don't want to do this, so hit Custom. You'll now see the initially created partition and, presumably, a large grey area underneath. Click this grey area to work with it.

Select Additional Mac Volume and type in a new size. The app puts a maximum size in there for you, but I found this to be different every time I opened it? Your Apple will crash if you do. Actually... it crashes and crashes and crashes... I can't successfully create a new secondary partition with Apple HD SC Setup. Onto the next tool...

Apple Drive Setup (Patched)

Apple Drive Setup was the defacto disk configuration utility with MacOS 8.1* and above. It also only supports Apple Firmware disks and so it turns out that it needs patching too!. Download Drive Setup 1.5 + patch or Drive Setup 1.7.3 and patch.

Download the version you want and the patch. Drive Setup will mount a disk on the desktop; copy the Drive Setup application from it to a folder somewhere. Then extract the patch into this folder also. Double-click the patch... not much happens. Opening Drive Setup will allow you to update your Hard Disk drivers... do this. You'll then need to reboot.

drive-setup-1 drive-setup-2 drive-setup-3

Turns out that when partitioning with Drive Setup, you cannot just add partitions. You need to select the 'layout' and then resize each individual new partition accordingly. You'll also need to realise that changing the 'layout' will wipe your current disk... entirely!

Drive Setup 1.5 also wont let you create a partition bigger than 4gb. I actually managed to create a 9gb Partition via Apple HD SC Setup and this just kept crashing MacOS 8.1 when trying to get to the desktop. Using Drive Setup to create 4 4gb partitions worked a lot better!

FWB Hard Disk Toolkit

You could also possibly use 2.5.3 is also available or . I couldn't get 4.5.2 to load on MacOS 8.1. Note that 2.5.3 is a full CDR image and takes forever to extract on the Quadra via StuffIt Expander.

Making a Macintosh Boot Disk (1.44mb)

Instructions are from here, here and here. Disk images: System 6.0.8 Boot Disk or System 7.0.1 Boot Disk. Note that if you want to install A/UX, you'll need a boot disk. It's included in the download and all is explained here.

I went to local PC store and bought an internal floppy drive and blank disks. I got home that afternoon and tore my windows desktop case open. Lots of mess only to find that there was no floppy plug on the motherboard. Hah. Fortunately I had a spare pc in the cupboard, so I yanked that open and, luckily, managed to install the floppy drive.

Keeping this machine off the internet, as it was archaic and bound to cause issues against my main workstation, I built the disks. The first goal was to write the A/UX boot disk that comes with the download. I opened the image in WinImage and ... it showed the main window with zero contents. There was no "Mac" footer in the status bar and I was concerned. Either way, I hit CTRL-W and wrote the floppy that was in the drive. It warned me that the disk wasn't empty... it was a blank disk anyway? I quickly checked in explorer for any files, but there was nothing.

Either way, I continued the write and it chugged along to 100% and told me it was finished. I trusted it.

Slapping the disk in the Macintosh, it booted. No magical short-cuts of any kind... it just trusted that the disk inserted was the one it was to take priority on. It loaded to a monochrome desktop and a dialog came up stating that we were installing A/UX! Winner... then it asked me where the CD was. Apparently it couldn't find it.... more on that here...

From this... I assume that the standard System 7 and 8 images will 'just work'(tm) Godspeed!

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About stevenh

Trains... trains... trains... + Electronics + Japan.
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