In comp.sys.apple2 Michael Pender <[EMAIL PROTECTED]> wrote: > I remember that back-in-the-day (BITD?) there were disk utilities that > changed the interleave between DOS disk sectors to speed up file transfer. > That is, physical sector 0 and logical sector 0 are always the same, but > physical sector 1 and logical sector 1 could be different. Is this a > similar problem?
It's similar. Sectors have a physical order (by default written straight from 0 to 15) and a logical order (skewed around). The mapping between them is fixed for each filesystem, and is different for DOS, Pascal/ProDOS, and CP/M. (It happens that logical sector 0 is mapped to physical sector 0 in all established formats, which means that you'll see track 0 sector 0 at the start of every disk image regardless of ordering.) The "fast skew" programs couldn't change the mapping between physical and logical sectors, but they could write the physical sectors in a different order by reformatting the tracks. Quality Software's Bag of Tricks was one such utility. This sort of re-skewing would only be noticeable by software that handles nibble images, because an RWTS read of sector 5 will always map to the same physical sector. The trouble with ".DSK" images is that they were either written as a series of 256-byte sectors (sector 0, 1, 2, 3, ...) or a series of 512-byte ProDOS/Pascal blocks (sector 0, 2, 4, 6, ...). If you assume that track 0 sector 1 starts 256 bytes into the disk image file, you may be disappointed. Naming 5.25" disk images with ".DSK" is a mistake, IMHO. They should be ".PO" or ".DO" to identify the contents unambiguously. If I recall correctly, early versions of KEGS assumed that 5.25" disks were in DOS order and 3.5" disks were in ProDOS order, so failing to label a disk image could get you into trouble. -- Send mail to [EMAIL PROTECTED] (Andy McFadden) - http://www.fadden.com/ CD-Recordable FAQ - http://www.cdrfaq.org/ CiderPress Apple II archive utility for Windows - http://www.faddensoft.com/ Fight Internet Spam - http://spam.abuse.net/spam/ & http://spamcop.net/ Steve Conrad 810 Main Henrietta, MO 64036 816-494-5692 http://sasha91.0pi.com www.fortunecity.com/rivendell/stonekeep/600 It is no secret (nor should it come as any surprise) that humankind's most noble impulses often surface during the most trying of times, that human spirit rises to the challenge when faced with adversity, that human strength is born from human failings...Is it any wonder, then, that the SDF-1 crew became a tighter family after the fortress had been exiled than it had before? From the log of Captain (later Admiral) Henry Gloval -- Apple2list is sponsored by <http://lowendmac.com/> and... / Buy books, CDs, videos, and more from Amazon.com \ / <http://www.amazon.com/exec/obidos/redirect-home/lowendmac> \ Support Low End Mac <http://lowendmac.com/lists/support.html> Apple2list info: <http://lowendmac.com/lists/apple2.html> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/apple2list%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
