From: "Patrick Rigney" <patrick(a)evocative.com> FYI, I found this while trolling through some links on retroarchive.org. Excerpt (edited) from an Arpanet message dated 17-feb-1984: "When I ordered CP/M the first time and it didn't work, I called Heath and they said "Oh, yeah, you need a hardware upgrade!" So I did the following: 1) Replaced the 444-42 in U517 with a 444-66 2) Connect a jumper from the middle pin of U503 to pin 17 of P509 They assured me this would work. However, to make the full upgrade, I could also do: 3) Replace the 444-40 in U518 with a 444-62 4) Replace the 444-43 in U550 with a 444-61 If I did this, I would lose cassette capability. Since this wasn't necessary (they said) I decided to just do 1 & 2. When I did this and it still didn't work, I called Heath again. They said it should have worked and my disk must be bad. So they sent me a new disk..guess what, still didn't work. Then they say hardware problem with the disk drive. That's when I put my problem on the net. Mr. D. C. Finch of Phoenix was kind enough to write me a letter (they have R/O access to the net) which told me that indeed 3 & 4 were necessary (at least for CP/M 2.2.03 and later). So this morning I called Heath again and they said, "That's right, you have to replace all three chips!" Just wish they had said that back in November!! I'll be happy to give anyone the details of Mr. Finch's letter if asked, I don't think most people are that interested.