Mac128 kindly emailed me a couple disk images. I found that the first image he sent to me ("2041HD20 copy.img") boots my Mac 512k just fine. I put version 1.1 of the HD20 INIT on it and rebooted. It now shows "Disassembler Installer" in the Welcome to Macintosh box and it does indeed format 800k disks as MFS (in my external 800k floppy drive)! Yeah! So clearly, something is unique about this System 2.0 file!

Since Mac128 mentions a "Update Disk" I would like to add that one of the five System 2.0's I tested yesterday was taken from a MAY 1985 System Update disk that has System 2.0 and Finder 4.1 on it. But clearly this "already updated" disk was not updated in quite the same way as Mac128's disk was! Because like I said in my post yesterday, I tried System 2.0 and Finder 4.1 from five different sources, and the HD20 INIT would not load at all (hence, it could not see or erase 800k disks).

So after successfully testing Mac128's "magic" disk today, I then decided to test my own copy System 3.2 and Finder 4.1 and the HD20 INIT (as Mac128 asked me to do in his post yesterday), but this acts just like System 3.0 & Finder 4.1, which I reported in my previous post (it can see and format 800k disks, but only as HFS). I then pulled System 3.3 off an Apple WorkStation Installer disk (with Appleshare 1.1) and combined that with Finder 4.1 and the HD20 INIT. Nope. Still acts like my System 3.0 and Finder 4.1 test disk did.

So it is quite clear that formatting 800k disks as MFS requires a very special copy of System 2.0 to work! (Or another, older System that has whatever "magic" resources are necessary to make 800k MFS disks in conjunction with the HD20 INIT).

And so, I decided it would be prudent to compare my System 2.0 file (which cannot make MFS 800k disks) with the "magic" System 2.0 file Mac128 sent me. I compared the files using ResEdit. Here are the general differences I spotted (resources I don't mention below "look the same" to me):

JDW's System 2.0 File (i.e., "Normal" System 2.0)

• no bmaps resource
  no ctabs resource
  ALRTs: ID -15775
  DITLs: -15936=30, -15775=52, -15776=174
  DLOGs: -15936=29, -15776=21
  DRVRs: fewer in number
  no LDEF resource
  no NBPC resource
  no ncts resource
  no nrct resource
  PACKs: fewer in number
  has PAPA resource
  no PTCH resource
  no tlst resource
  no WIND resource
  

Mac128's System 2.0 File (i.e., "Magic" System 2.0)

• has bmaps resource
  has ctabs resource
  ALRTs: ID -15808
  DITLs: -15808=242, -15807=52, -15775=38, -15776=182
  DLOGs: -15808=28, -15807=34, -15776=28, -15775=21
  DRVRs: more in number
  has LDEF resource
  has NBPC resource
  has ncts resource
  has nrct resource
  PACKs: more in number
  no PAPA resource
  has PTCH resource
  has tlst resource
  has WIND resource

Before I do any further testing, I would appreciate hearing everyone's thoughts on this.