Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!PUCC.PRINCETON.EDU!MQUINN%UTCVM From: MQUINN%UTCVM@PUCC.PRINCETON.EDU Newsgroups: comp.sys.apple2 Subject: Re: 3.5" disk hardware questions Message-ID: <9012021742.AA00237@apple.com> Date: 2 Dec 90 00:21:31 GMT References: Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 63 On Sat, 1 Dec 90 12:27:40 CST John D. Baker said: >I have a few questions regarding Apple 3.5" disk equipment. > >What exactly makes the UniDisk 3.5 so different from the other >Apple-compatible 3.5" drives. Why can't one sector-edit a >UniDisk 3.5 while other 3.5"drives _can_ be sector-edited? > >If the UniDisk 3.5s are so different from the others, how can >AMR and AE make a 3.5" drive that can be used on both Apple >][s, ][+s, and //es with the 3.5" disk controller AND the //c, >//c+ and ][gs Smartport? Well, I don't know if you were aware of this, but Apple makes -two- 3.5" 800k drves (the Apple 3.5" Unidisk drive and the Apple 3.5" drive). They're virtually identical in operation, except, the Unidisk is a little 'smarter'. The Unidisk has firmware IN the drive that reads one 'block' at a time. The Apple 3.5" drive doesn't have this, so the computer has to tell the drive EXACTLY -HOW- to read each block, which, supposively, takes a little more time. The Unidisk already 'knows' how to read a block, so all the computer has to tell it to do is -WHICH- block to read. Because of this, the computer can't take complete control of the Unidisk drive to do sector editing, track examination, nibble editing, etc. All the computer can do to a Unidisk is tell it which block to read or write and the drive does the rest. Since the Apple 3.5" drive doesn't have this 'capability', the computer has to tell it -everything- to do. Which track to move to, how far to move the drive arm, which head to access, and what bytes need to be written or read to the blocks, sectors, tracks, sync bytes, address fields..... So, with the Apple 3.5" drive, there's nothing preventing you from doing a sector edit. The AMR & AE drives are, basically, Apple 3.5" drive clones (I think). Both the Unidisk 3.5" and the Apple 3.5" drives were designed to use the smartport. (here's some speculation, can someone confirm or 'un'confirm this?)... ProDOS probably looks to see which kind of drive is connected. If it's the Unidisk, then ProDOS only says, "read or write block #xxxx". If it's the Apple 3.5" drive, ProDOS goes ahead with all the technicle details of finding the track, head, & sectors, then actually does the writing. >In other news: > >Way back when the Chinook CT20c and CT40c had just come out, I read >that they could also be attached to a //e via the UniDisk 3.5 >controller card. How is this possible? In fact, it was in a >copy of inCider (arrgh!) at the time (in their review, in fact!). > >Please elaborate, as it sounds like a quick and sneaky way to add a >hard disk to a //e (3.5 controllers are easily obtainable and much >less expensive than a EssSeeEssEye card). The Hard drive probably makes ProDOS think that it's a Unidisk. All ProDOS is concerned with is block information, so the smartport device (the HD in this case) can have just about any number of blocks available for prodos to access. >Thanks for the help. > >John D. Baker ->An Apple 5.25", 3.5", 8" ZCPR3 nut // ---------------------------------------- Michael J. Quinn University of Tennessee at Chattanooga BITNET-- mquinn@utcvm pro-line-- mquinn@pro-gsplus.cts.com