Next, I am assuming their use of "new Apple file system" actually means "Hierarchical File System" (HFS). If so, that would imply compliance with the 128k ROMs, rather than the 64k ROMs. :-/ It is also interesting to note that Apple introduced HFS in September 1985, and this visit to Levco was made on October 6th, 1985.

Click to expand...

That may be specious reasoning. The HD20 is "compliant" with 128K ROMs, which mainly means HFS. At the time Levco was developing their SCSI interface board, HFS was the giant rumor in the Mac community and compatibility with the next generation Mac Plus was paramount to success within the industry. Whether in ROM or RAM, any product that hoped to survive for the Mac had to be able to support the 128K ROM changes, just like the HD20 did on the 512K with software. In other words, anything written for the Mac Plus would also work on the Levco board, whether it was clipped to a 64K ROM Mac or not. On the other hand, I don't think there is anything that otherwise prevents a SCSI drive from being formatted MFS, though to be compatible with the 128K ROMs, the option to format HFS would be a requirement. On the other hand, the the Levco patch ROMs (used instead of software drivers to enable booting) may have loaded HFS code, just like the 128K ROM or the HD20 INIT. But I don't think that makes it a 128K machine, no more than the HD20 INIT does. In order to make it bootable, the piggy-backed ROMs are simply a different delivery method for the software, directly injected into the system ROMs rather than taken internally after loading.

While we're on the subject of HFS compatibility, I found this reference to the Rev. 64K ROM (I assume) being released in March '85, allegedly to support changes in the 400K drive. However, this article indicates that it is needed to support the new 800K drive compatibility and that for some reason the older ROMs couldn't. Is it possible that 2nd gen. 64K ROMs had the 800K drivers built-in? After all, the HD20 was announced in April '85, though not delivered until September. In which case, such a ROM would not require the HD20 INIT to access them ... could this also have something to do with System 5 not booting on a 512K Mac on the first gen. ROMs? Or, does this article refer to 128K ROMs being put into 512K Macs? Very curious wither way. I guess I need to do a ROM dump from my Rev. B ROMs and find out ...

http://www.mactech.com/articles/mactech/Vol.02/02.01/Jan86Mousehole/index.html

But I am left to wonder ... even if all of these solutions, John Bass' included, can be implemented on the 64K ROM, will they ultimately preserve the 64K ROM experience or will they alter it in some was so as to cause compatibility issues? In particular, I am hard pressed to understand how Bass' SCSI implementation will be bootable, or is it simply a hand-off solution like the HD20? Without a deeper understanding I would think simply using an external SCSI drive as a storage unit would be the best one could hope to do on a 64K ROM. I suppose a hand-off solution is possible, but an INIT that patches ROM extremely early-on would need to be written to do that. Simply switching to the external System would not be a true bootable experience as many drivers must be loaded earlier in the startup procedure than this allows. And then there are the exact same issues that plagued the HD20: none of the software was designed to be written to large volumes, so there were many incompatibilities from installation to running software off the HD20. This was true of the serial hard drives as well.