Sender: eric@ruckus.brouhaha.com From: Eric Smith Newsgroups: alt.folklore.computers,comp.sys.mac.programmer.tools,comp.sys.mac.programmer.misc Subject: Apple hard drives, non-SCSI (was Re: Macintosh BASIC from Micro$oft) References: <388AD0DB.EDFEC47F@plano.net> <3891e70c.9491739@news.psi.ca> <86t1ln$cs4$1@hawkins.cba.uni.edu> <38922129.24370531@news.psi.ca> X-Disclaimer: Everything I write is false. Organization: Eric Conspiracy Secret Labs X-Eric-Conspiracy: There is no conspiracy. Date: 28 Jan 2000 23:34:58 -0800 Message-ID: Lines: 36 X-Newsreader: Gnus v5.5/Emacs 20.3 NNTP-Posting-Host: ruckus.brouhaha.com X-Trace: 29 Jan 2000 00:20:51 -0800, ruckus.brouhaha.com Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.ifi.unizh.ch!newsfeed.rhein-neckar.de!news.rhein-neckar.de!newsfeed.ision.net!ision!news.vas-net.net!newsfeed.icl.net!netnews.com!howland.erols.net!news.sgi.com!news.spies.com!ruckus.brouhaha.com Xref: chonsp.franklin.ch alt.folklore.computers:49285 jmiller@istar.ca (John Miller) writes: > Apples first external, just before the Mac Plus, used either the > floppy port or the serial port. You're referring to Apple's HD-20 (*not* the later HD-20SC, which was SCSI). It used the floppy interface. They used the IWM floppy controller to send and receive data packets from the drive, similarly to (but not compatible with) what was done on later Apple ][ computers as "SmartPort". Due to limitations of the IWM (and the Apple ][ FDC it was derived from), it was not possible to transfer eight bits per byte. The data had to be rearranged from the user buffer of 524 bytes (512 data, 12 tag) into a larger buffer encoded to meet the requirements of the IWM. One of the requirements of the IWM is that the MSB of every byte must be set. The floppy drive imposes additional requirements so that it is generally not possible to get more than six data bits per byte (GCR coding), but because the HD-20 data transfers were synchronous to crystal clocks at both ends, it might be the case that the HD-20 could forego GCR and use seven bits per byte. I don't recall. But the HD-20 wasn't Apple's first external hard drive. That distinction belongs to the five megabyte Profile drive, part number A9M-0005. (There was a later ten magabyte version). The Profile was used on the Apple ][, Apple ///, and Lisa (also known as Macintosh XL). Apple also made a non-SCSI 10 megabyte internal hard drive for the Lisa, known as the "Widget". The interface was electrically and functionally identical to that of the Profile, but as an internal drive it used an IDC header connector rather than a DB25. The Profile, Widget, and HD-20 all supported tags, and the Lisa and Macintosh file systems used them, but Apple gave up on tags after they switched to SCSI, since not all SCSI drives support formatting with sector sizes that are not a power of two. And no ATA (IDE) drives support it, as the ATA spec *requires* that the sector size be exactly 512 bytes.