question about padding disk image files

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Joined: Sun Mar 15, 2020 4:55 pm

question about padding disk image files

Post by davibear »

Please forgive my nubeness, but I'm a little confused.
I'm using DTC to read a 5 1/4" floppy from an HP 9836 ("Chipmunk"). Here are the disk specs from the HP documentation:

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    Tracks per disc:        35 per side, 70 total
    Sectors per track:      16
    Bytes per sector:       256 (362 including overhead bytes)
    Rotational speed:       300 RPM +/- 1.5% (+/- 4.5 RPM)
    Recording mode:         Modified Frequency Modulated (MFM)
    Tracks per inch:        48
    Bit density:            5456 BPI Track 34
    Sides per disc:         2
    Bytes per disc:         286,720 (formatted), 420,000 (unformatted)
    User available tracks:  66
    Total capacity:         264K bytes
    Media:                  133 mm (5 1/4-in.) double-sided,
                            double-density flexible disc
Here's the DTC command I'm using:

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$ dtc -fdiskimage.raw  -d0 -dd0 -s0 -e68 -v300 -k2 -i0 -fdiskimage.img -d0 -dd0 -s0 -e68  -z1 -v300 -n16 -k2 -i4
It works just fine, but the resultant file 'diskimage.raw' is 327680 bytes long. I'd expect a file that's 2 * 35 * 16 * 256 = 286720 bytes long.
Indeed if I look at the file its contents look absolutely correct all the way up to byte [286719]. The rest of the file is zeroes.
Why is DTC adding padding? Am I doing something wrong with my command line?
Thanks very much!

Posts: 611
Joined: Tue Dec 06, 2011 9:09 pm

Re: question about padding disk image files

Post by ZrX »

Not sure off the head, but try placing the -e68 after -i4.

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