shad04@ccu.umanitoba.ca (Dan Fandrich) (02/15/90)
I received two responses to my query about CBM floppy disk formats (from
Marcel LeBlanc <leblanc@eecg.toronto.edu> and Romulis
<s887212@minyos.xx.rmit.oz.au>). I am posting it on behalf of all those
1581 and other "oddball" drive owners who are teed off at C64 programmers
who think that all disk directories are located on track 18, sector 1 (on
device 8 at that!). (Before you flame, I mean oddball drives, not oddball
owners!)
This summary should allow programs to be written with a measure of device
independence when they access floppy disk sectors directly. The type of
disk drive attached may be detected by reading the error channel (15) after
sending the command "UJ" and waiting a moment. The resulting pseudo error
code 73 should be searched, looking for the drive type while ignoring
version numbers and copyright notices.
Following is my summary of disk formats used for various Commodore disk
drives. Questions marks take the place of any information I don't have.
My thanks to Marcel and Romulis for their input.
1540, 1541, 1571 (in 1541 mode), 2031, 2040, 4040:
--------------------------------------------------
1 side
35 tracks
trks 1-17: 21 sectors/trk
trks 18-24: 19 sectors/trk
trks 25-30: 18 sectors/trk
trks 31-35: 17 sectors/trk
Directory header at t18 s0 (pointer to start of directory at bytes 0 & 1)
BAM starts at t18 s0
BAM takes up 1 sector
Directory starts at t18 s1
Directory takes up 18 sectors
Free blocks: 664
Power-on message (for 1541): 73,CBM DOS V2.6 1541,00,00
Power-on message (for 1540): ?
Power-on message (for 1571): ?
Power-on message (for 2031): ?
Power-on message (for 2040): ?
Power-on message (for 4040): ?
1581:
--------------------------------------------------
1 logical side (2 physical sides)
80 tracks
trks 1-80: 40 logical sectors/trk (sectors 20-39 are on physical side 2)
Directory header at t40 s0 (pointer to start of directory at bytes 0 & 1)
BAM starts at t40 s1
BAM takes up 2 sectors
Directory starts at t40 s3
Directory takes up 37 sectors
Free blocks: 3160
Power-on message: 73,COPYRIGHT CBM DOS V10 1581,00,00
8050:
--------------------------------------------------
1 side
77 tracks
trks 1-39: 29 sectors/trk
trks 40-53: 27 sectors/trk
trks 54-64: 25 sectors/trk
trks 65-77: 23 sectors/trk
Directory header at ?
BAM starts at t38 s?
BAM takes up ? sectors
Directory starts at t39 s?
Directory takes up ? sectors
Free blocks: 2052
Power-on message: ?
8250, SFD-1001 (?):
--------------------------------------------------
1 logical side (2 physical sides)
154 tracks (77 tracks/side x 2 sides)
trks 1-39: 29 sectors/trk (on physical side 1)
trks 40-53: 27 sectors/trk " " " "
trks 54-64: 25 sectors/trk " " " "
trks 65-77: 23 sectors/trk " " " "
trks 78-116: 29 sectors/trk (on physical side 2)
trks 117-130: 27 sectors/trk " " " "
trks 131-141: 25 sectors/trk " " " "
trks 142-154: 23 sectors/trk " " " "
Directory header at ?
BAM starts at t38 s?
BAM takes up ? sectors
Directory starts at t39 s?
Directory takes up ? sectors
Free blocks: 4133
Power-on message (for 8250): ?
Power-on message (for SFD-1001): ?
--
>>> Dan Fandrich
CDNnet: shad04@ccu.umanitoba.ca
Compu$erve: 72365,306wbks@tygra.UUCP (Sean Burke) (02/16/90)
I wonder why commodore has the 1581 set up in the strange way it does? I mean, why not just use the physical disk format instead of having to run everything through the drive controller. I believe that drive access would have been sped up considerably this way. A small side note: Has anyone had any experience with the 3.5" version of 128 CP/M? If so, what disk formats will it handle? Thanks. Remember, Save your commie 8-bit, it still kicks the $%$%# out of many higher priced computers. -- = CAT-TALK Conferencing Network, Prototype Computer Conferencing System = - 1-800-825-3069, 300/1200/2400/9600 baud, 8/N/1. New users use 'new' - = as a login id. <<Redistribution to GEnie PROHIBITED!!!>>> = E-MAIL Address: wbks%tygra.uucp@sharkey.cc.umich.edu
leblanc@eecg.toronto.edu (Marcel LeBlanc) (02/16/90)
In article <15@tygra.UUCP> wbks@tygra.UUCP (Sean Burke) writes: >I wonder why commodore has the 1581 set up in the strange way it does? >I mean, why not just use the physical disk format instead of having to run >everything through the drive controller. I believe that drive access would >have been sped up considerably this way. You should check your facts before complaining about Commodore's organization of the 1581. The logical vs. physical organization maintains a better level of compatibility with the 1541 (a single sided device). This also hides the fact that 1581 physical sectors are 512 bytes in length The logical to physical translation requires a trivial amount of time. The 'drive controller' doesn't do any of this. Removing the logical to physical translation step wouldn't speed up the 1581 at all. With most fast loaders (that can handle the 1581), the load/save speed on the 1581 is 10x the speed of a 1541. Marcel A. LeBlanc | University of Toronto -- Toronto, Canada "leblanc@eecg.toronto.edu" | and: LMS Technologies Ltd, Fredericton, NB, Canada ------------------------------------------------------------------------------- UUCP: uunet!utai!eecg!leblanc BITNET: leblanc@eecg.utoronto[.ca]