Question: 128k/512k and 800k drive

[LaPorta]

I’ve got a bunch of 128k/512k MBs that I’m going to try and resurrect for other’s machines. To test them, however, I was wondering if it would be possible to use an 800k drive with 400k disks, or if the IWM on the logic board won’t be able to run the drive at all.

 

[Gorgonops]

The IWM isn't a problem, but the ROM is. To make a long story short trying to use an 800k drive with the original 64k Mac ROMs results in a divide-by-zero error because a bug in said ROMs gets triggered if there isn't a constant slight variance in the tachometer readings, which the 800k drive doesn't provide. (Remember, the 400k drive's speed was directly controlled by a PWM signal generated by the Mac and adjusted based on tach feedback, while the 800k drive self-regulates its speed based on what track the head's on.)

You could slap a set of Plus ROMs into the boards for testing, if need be. That essentially would temporarily convert them to 128ke(an unofficial designation for such a Frankenstein)/512ke's that are fully compatible with the 800k drive.

 

[LaPorta]

That I can do, thanks. I’ve got enough of those Plus ROMs around. I’ve got a few 400ks now as well, but none have been cleaned or set up so the ROM swap would be easiest.

 

[NJRoadfan]

I've run the Apple 3.5" Drive (with eject button, from an Apple IIgs, not the earlier Mac version) on a Mac 512k without any problem. You can even use it as an 800k drive by loading the HD20 Init.

 

[Dog Cow]

I’ve got a bunch of 128k/512k MBs that I’m going to try and resurrect for other’s machines. To test them, however, I was wondering if it would be possible to use an 800k drive with 400k disks, or if the IWM on the logic board won’t be able to run the drive at all.

Yes, you can use the 800K Apple 3.5 Drive, Model No. A9M0106 with a stock Mac 128K or 512K, without any additional hardware or software.

This drive can boot both 400K and 800K MFS disks. This is neat: boot the AppleShare Workstation disk or Hard Disk 20 startup disk. At first the drive will have a rough seeking sound. Then when Welcome to Macintosh comes on screen and the new Sony driver is loaded into RAM and activated, the seeking sound will change to be smooth like usual.

 

[Gorgonops]

I've run the Apple 3.5" Drive (with eject button, from an Apple IIgs, not the earlier Mac version) on a Mac 512k without any problem. You can even use it as an 800k drive by loading the HD20 Init.

Yes, that particular drive works because Apple did some "magic" the tach signal that sidesteps the bug in the 64k ROM. The internal 800k drive mechanisms (or the "original" Mac-styled 800k drive) are the ones with the problem.

 

[LaPorta]

Even more helpful. I’ve got plenty external 800ks like that.

 

[Gorgonops]

Even more helpful. I’ve got plenty external 800ks like that.

Then you should be good good to go. I probably should have mentioned that myself since I have first-hand experience that my 512k-no-e can boot from a IIgs drive connected externally.

 

[PB145B]

Yes, you can use the 800K Apple 3.5 Drive, Model No. A9M0106 with a stock Mac 128K or 512K, without any additional hardware or software.

This drive can boot both 400K and 800K MFS disks. This is neat: boot the AppleShare Workstation disk or Hard Disk 20 startup disk. At first the drive will have a rough seeking sound. Then when Welcome to Macintosh comes on screen and the new Sony driver is loaded into RAM and activated, the seeking sound will change to be smooth like usual.

Wow, that’s awesome! Didn’t know that.  

I’ve got one of those drives, so I will be doing some experimenting tonight...

 

[Crutch]

Vague warning that the 128ke is not a great setup - as I recall the 128k ROM loads HFS into RAM, or something, eating up precious kilobytes?