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davidgiven
would like to be able to archive mysterious 81st cylinder on DEC RX50 diskettes
I have some original DEC RX50 diskettes I'd like to archive.
$ ./fluxengine read rx50 -s drive:0 -o test.img --copy-flux-to test.flux
So far, so good. A friend pointed out that the 81st cylinder of a real RX50 has extra identifying information in it:
$ ./fluxengine read ibm -s drive:0 -o test_cyl80.img --copy-flux-to test_cyl80.flux -c 80 -h 0 --encoder.ibm.trackdata.use_fm=1
$ hexdump test_cyl80.img
000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >................<
*
002800 46 4d 54 20 4d 46 4d 20 4e 4f 2f 46 43 20 31 2a >FMT MFM NO/FC 1*<
002810 31 30 2a 35 31 32 20 38 30 54 20 2d 44 45 43 20 >10*512 80T -DEC <
002820 52 58 35 30 00 20 20 20 32 32 32 36 34 2d 32 33 >RX50. 22264-23<
002830 20 20 01 07 84 12 22 22 20 46 01 f5 30 30 30 30 > ...."" F..0000<
002840 30 f3 31 20 20 20 20 20 20 20 20 20 20 20 20 20 >0.1 <
002850 20 20 20 20 82 f1 c8 54 9a fd ce 57 9b 7d 0e b7 > ...T...W.}..<
002860 6b 05 20 20 20 20 20 20 20 20 20 20 20 20 20 20 >k. <
002870 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 > <
002880
Is there a way to glue these two .flux files together for archival purposes? Or, better yet, is it possible that the 'rx50' format could know that there may be an 81st, FM-formatted cylinder? Thanks in advance!
Well, that's special... FM encoding, no less?
Do you have a reference? I can't find it anywhere in the documentation I've seen. Are you sure that track was added by the RX50, and not by some other imaging software? One option is that if DEC didn't let you format your own disks, it might be identifying information written by DEC's bulk formatter and never intended to be accessible by normal humans.
Yes, I believe it is FM encoding. No, sadly, I have no documentation that describes this. For fun I went back through all of my DEC Professional RX50 diskettes and scanned the 81st cylinders. Only the newer DEC-issued releases had data there. I wrote a program to go through all of the images, compare the 128 bytes there and find those bytes that were always the same and those that differed:
Common data (locations with variations marked with __):
00: 46 4d 54 20 4d 46 4d 20 4e 4f 2f 46 43 20 31 2a |FMT MFM NO/FC 1*|
10: 31 30 2a 35 31 32 20 38 30 54 20 2d 44 45 43 20 |10*512 80T -DEC |
20: 52 58 35 30 00 20 20 20 32 32 32 36 34 2d 32 33 |RX50. 22264-23|
30: 20 20 __ __ 84 __ __ __ 20 46 01 f5 30 30 __ 30 | __.___ F..00_0|
40: __ __ __ 20 20 20 20 20 20 20 20 20 20 20 20 20 |___ |
50: 20 20 20 20 82 f1 c8 54 9a fd ce 57 9b 7d 0e b7 | ...T...W.}..|
60: 6b 05 20 20 20 20 20 20 20 20 20 20 20 20 20 20 |k. |
70: 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
Variations:
offset
32 33 35 36 37 3e 40 41 42
file -----------------------------------
BL-AI19C-BH 04 02 10 34 19 30 31 35 30
BL-CF74C-BH 03 26 00 01 36 30 30 39 30
BL-CF74C-BH 03 26 00 03 45 30 30 39 30
BL-CL73B-BH 11 10 00 53 44 30 30 37 31
BL-HC42A-BH 04 09 19 59 54 30 31 33 30
BL-HD04A-BH 01 21 17 26 09 30 31 34 30
BL-HD04B-BH 01 07 11 34 01 30 30 f3 31
BL-HD04B-BH 06 18 02 24 01 30 30 31 30
BL-HD05A-BH 01 22 02 33 40 30 32 30 31
BL-HD05B-BH 02 11 19 59 51 30 30 30 31
BL-HD05B-BH 02 11 20 00 55 30 30 30 31
BL-HD06A-BH 01 03 13 31 10 30 30 34 30
BL-HD06B-BH 06 18 05 08 58 30 30 35 31
BL-HD06B-BH 06 18 05 07 54 30 30 35 31
BL-HD07B-BH 06 18 01 42 23 30 31 38 30
BL-HD07B-BH 06 18 01 43 28 30 31 38 30
BL-HD07B-BH 01 07 12 22 22 30 30 f3 31
BL-HD08B-BH 01 07 13 51 38 30 30 f3 30
BL-HD08B-BH 01 19 12 45 32 30 31 38 30
BL-HD08B-BH 01 07 13 52 42 30 30 f3 30
BL-HD09B-BH 01 07 13 05 38 30 30 f3 31
BL-HD09B-BH 01 17 05 34 48 30 31 39 30
BL-HD09B-BH 01 07 13 04 33 30 30 f3 31
BL-HD10B-BH 06 18 09 43 45 30 30 35 30
BL-HD10B-BH 06 18 05 45 16 30 31 39 30
BL-HD10B-BH 01 20 19 22 06 30 30 30 31
BL-HD11B-BH 01 17 06 05 36 30 30 31 31
BL-HD11B-BH 01 17 06 06 41 30 30 31 31
BL-JB90B-BH 06 17 14 45 00 30 31 31 30
BL-JB90B-BH 06 18 12 29 42 30 32 30 30
BL-JB90B-BH 06 17 14 46 03 30 31 31 30
BL-JB91B-BH 06 18 12 43 59 30 30 39 30
BL-JB91B-BH 01 13 12 01 21 30 30 30 30
BL-JB92B-BH 01 15 16 03 31 30 30 36 30
BL-KS73A-BH 06 04 09 36 40 30 30 30 30
BL-N596F-BH 01 03 10 09 00 30 31 31 30
BL-N596G-BH 07 03 18 02 08 34 39 36 31
BL-N605G-BH 02 13 01 12 58 30 32 30 31
BL-N631H-BH 12 16 15 41 36 30 31 33 30
BL-N631I-BH 01 19 10 28 32 30 30 35 30
BL-N633G-BH 12 11 03 48 40 30 30 32 30
BL-N633H-BH 03 05 14 21 50 30 30 33 30
BL-N634G-BH 07 03 17 00 26 30 30 31 30
BL-N638F-BH 12 05 19 13 38 30 31 32 31
BL-N639H-BH 03 26 02 32 50 30 30 39 30
BL-N640G-BH 03 26 00 59 57 30 30 31 30
BL-N640G-BH 03 26 04 41 36 30 30 34 30
BL-V444B-BH 12 13 02 51 00 30 31 34 30
BL-Y472B-BH 03 20 08 21 38 30 31 32 31
BL-Y982D-BH 03 05 20 02 57 30 31 39 30
BL-Y982D-BH 07 03 15 48 31 30 30 37 31
BL-Z934D-BH 04 10 04 16 13 30 30 33 30
-----------
MIN 01 02 00 00 00 30 30 30 30
MAX 12 26 20 59 59 34 39 f3 31
NVALS 08 12 14 22 21 02 04 0b 02
OR 17 3f 3f 7f 7f 34 3b ff 31
AND 00 00 00 00 00 30 30 30 30
Key
MIN is the minimum value seen
MAX is the maximum value seen
NVALS is the count of unique values seen
OR values have a 1 for every bit that is ever 1
AND values have a 1 for every bit that is always 1
Notice that the values change in some cases for different copies of the same diskette. For example, all 3 of my copies of BL-HD10B-BH have differing values in the changing locations. In fact, no two diskettes had the exact same data in this section. Given the values that I see, I suspect the value at 0x32 is a BCD month, 0x33 is a BCD day-of-the-month, 0x35, 0x36, and 0x37 are the BCD hour (24 form), minute, and second. Logically, this would make the value at 0x34 the BCD year, but it's always 0x84, and some of this software (e.g., BL-Y982D-BH) was released as late as 1987. Because the data are encoded in FM, I don't think the DEC Professional controller can even read them, let alone write them. So I think you're probably correct -- these are data placed there by the duplicator. I was hoping that there would be a unique key to identify a master, but that doesn't appear to be the case.
FWIW a lot of other commercial copiers leave similar information, I've seen it on all sorts of commercial IBM-formatted disks. Usually the sector format disregards the rest of the floppy, which makes it hard to put into most image formats (plus it would likely confuse some software).
