Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!mit-eddie!bloom-beacon!eru!hagbard!sunic!news.funet.fi!tut!tm86214 From: tm86214@tut.fi (T. M. Miettinen) Newsgroups: comp.sys.amiga Subject: Re: Reading 1581 disks Message-ID: Date: 27 Sep 90 21:10:54 GMT References: <2041@lpami.wimsey.bc.ca> Sender: news@funet.fi (#News ) Organization: Tampere Univ. of Technology, Finland. Lines: 32 In-Reply-To: lphillips@lpami.wimsey.bc.ca's message of 25 Sep 90 11:20:58 GMT > In <439@cbmger.UUCP>, peterk@cbmger.UUCP (Peter Kittel GERMANY) writes: > >In article <1990Sep24.173635.2012@bushido.uucp> jamesb@bushido.uucp (Jim Harvey) writes: > >>The TRANSFER utility program that comes with the ReadySoft C64 Emulator II > >>will do this. It will also read a 1541 formatted disk in a 1020 drive, and > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > >>will read and write to a real 1541 drive with the use of an included adaptor. > > > >Is this REALLY true? With all the track-to-track read speed changes in > >the 1541 format? How do they manage that? Is the data density on a 1541 > >so small compared to an Amiga or PC that these variations can be easily > >followed by the decoding software? Sounds very interesting. > If memory serves, there were no track to track red speed changes... only a > smaller number of sectors per track as you approached the center of the disk. > This happened in zones. It's been a while though. I could be mistaken. I > do remember being a little baffled about this when Don Lekei and I were writing > DiskDoctor (the PET one, not the Amiga one). In fact, speed was (is?) not varied, but the data clock rate did change, being at track 1 about 25% higher than at track 35. Thus more sectors could fit into single track (21?? vs 16). The lowest speed of the four was the same used in many CP/M machines. If 1541 used only this data rate, disk capacity would have been 35*16*256 bytes=140 KB (Yuk!!). Did you know that aside these speed tricks, you could also read tracks between those normal ones, but as the erase head was too wide, writing to them erased both neighbor tracks!! If you only changed the R/W head (70..80*21*256=430K)... However, this has nothing to do with 1581. I think this is the new? 3.5 inch drive, but I've never seen it. - Topi Miettinen tm86214@tut.fi Topi Miettinen Wake up; Time to die! horrormoviesAmigaTDe Tiaisentie 17 D -Leon's last words lectronicsRPGsleepeat SF-33100 Tampere in Blade Runner