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20SC Doesn't Mount

equant

Well-known member
This is one I thought I'd be able to find the answer to online, but had no luck.

I have an Apple 20SC, and it boots my Mac Plus just fine, but I'd like to mount it (not boot it) on my SE.

The SE won't mount the drive. I've even tried some of the SCSI control panels (schuzzy, SCSI Tools, MT. Evertyhiing, SCSIInfo), and nothing can boot it.

I'm guessing (and hoping) that this is a well known issue, and I'm doing something stupid. Anyone have ideas?

Thanks,

Nathan

 

equant

Well-known member
Oh yeah, the SCSI tools I've tried see it, and report the correct info about it. It's just that nothing happens when they try to mount the drive.

 

equill

Well-known member
If the external drive is formatted, most probably, with Apple's utility, it has an interleave factor of 3:1 for the Plus. The SE uses an interleave of 2:1. The ratios reflect the number of revolutions of a platter needed to read a complete track in the first Macs to have SCSI, and is necessary because the port speeds are 312kB/s and ~650kB/s. The SE is expecting data at twice the speed that the Plus can deliver.

If you have the original HDD in the external enclosure, possibly a Rodime 3.5-in or a Seagate 5.25-in, even reformatting the drives from a Mac that is capable of 1:1 interleave with an updated disk driver, such as the Mac II, may not get around the problem. If the present data can be saved elsewhere, you might care to try the reformatting path. A more modern drive (one of the smaller Quantum Pro ELS or LPS units) instead of whatever is in the enclosure now might just save the day for you.

de

 

equant

Well-known member
Ah. Thanks. I've read threads about this, but didn't put it together. I appreciate the help.

Nathan

 

equill

Well-known member
Depending as you wish to explore, or just to get a result, you could use a disk utility such as Silverlining 5.8.x to format the external HDD. These versions of Silverlining allow you to choose the interleave ratio. The GUI is not well developed, so you may have to feel your way about in the app. until you get the hang of it.

de

 

numero6

Active member
Hello everyone,

I'm having the same problem trying to mount a SC20 on my Performa 6400 : the disk is detected but does not mount.

I'd like to reformat the disk and install a fresh version of OS6 for my Plus. Is their any (hard or software) way to do that or does the interleave issue makes it impossible ? The Performa runs OS9.

Thanks

 

Charlieman

Well-known member
I'd like to reformat the disk and install a fresh version of OS6 for my Plus. Is their any (hard or software) way to do that or does the interleave issue makes it impossible ?
Decent third party formatters that will run on your 6400 will allow you to specify 3:1 interleave so that it will be usable on your Plus. However, the drive will be unusable on your 6400.

A better solution is to download the four 800KB System 6.0.x floppy disk images from Apple and create some real disks. Use the HDSC utility on the Disk Tools floppy to format the SC20, then reboot from the Install floppy to install System 6.

 

equill

Well-known member
The contemporary Apple HDD utility (available in the link that I gave above) also 'chooses' the appropriate interleave for the Plus (3:1), SE (2:1) and faster SCSI ports (1:1) subliminally. If the drive has already been formatted with another brand of utility/driver, only a hacked Apple utility (from gamba's site) will do the job of 'taking over' the drive from the non-Apple utility.

As Charlieman notes, Macs with 1:1-capable ports don't find it easy to cope with 3:1- and 2:1-formatted drives, so setup has to take place with the Mac that will use the HDD concerned. There is another current thread in these Forums dealing with the matter.

de

 

Mac128

Well-known member
Hey you guys with 20MB HD-20SC external drives ... you mind cracking those cases open and reporting on the drives living in there? The reason I ask is because one of the two variants of 20MB drives is supposed to work with an HD-20 IWM drive as discussed here: http://68kmla.org/forums/viewtopic.php?p=20427#20427

The one with components facing up (not the solder side) is supposed to be the one. Pictures would also be appreciated as I've looked all over the internet and nobody seems to have taken pictures of the internal workings of a "STOCK" HD-20SC, like JDW did with his HD 20. Thanks!

 

numero6

Active member
Ok guys, thank you for your answers, I'll try to boot from a floppy then and reformat the disk from the Plus.

About inside pictures of SC20 I'll post them in the appropriate post.

 
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