weak sectors?

[Fran123]

Hello

I'm with the Arkanoid 1 original disk. At track #1 there are sectors #79, #81, #82, #83, #84, #85, #86, #87 and #88. The size of sector #79 is 128 bytes, and 512 for the rest.  All of them are full of A7's.

Winape read without problem sector #82, but when it read sector #79 the result bytes are #40, #04 (no data), #00, #01, #79 and #02

Then, is the sector #79 a weak sector?

Thank you

[roudoudou]

It's not a weak sector, only a sector of 128 bytes that is not read. There is a check that the ID exists and that's it. Data inside does not matter.

If you write sector of 128 bytes, FDC will use a wrong Data Address Mark* and you cannot read anymore what you wrote.

Instead of #FB o #F8, FDC will use #FD and #FC and the data will "disappear". Sector of 128 bytes in double density if officially not supported.

On a weak sector, you will get CRC error instead of ND (and you will read something!)

[Johnny Olsen]

I would postulate that your disc is not original, it has been run once.
If you write protect your disc, a message would appear on the screen
where you were asked to remove the protection.

The first time you start the disc, the 1987 version speedlock will change
sector &81-&88 contents from bytes &A6 to &A7 and formats sector &79 from
512 bytes to 128 bytes.

If you then use a copy program to make a backup of your disk with a program
program like "ODDJOB" it would not be able to copy sector &79
When you run this copy there would be a message on the screen
"THIS DISC IS AN ILLEGAL COPY"
and the disk would be formatted.

Insert disc
"Arkanoid (UK) (1987) [Original] A6 Disc has not been run.dsk"
Check sector &79 and Sector &81-&88
run" disc
When the game is running, check sector &79 and Sector &81-&88 again.
the loader has changed the disk's sectors.

I have copied
"Arkanoid (UK) (1987) [Original] A7 Disc has been run.dsk"
with "Oddjob" and got two files
Arkanoid (UK) (1987) [Original] - Oddjob Copy - Tab protection ON.dsk
Arkanoid (UK) (1987) [Original] - Oddjob Copy - Tab protection OFF.dsk
Run these two discs
With tab protection on - a message will appear on the screen, without
protection - the disk will be formatted.
WinApe cannot save the disks so you have to check the sectors without
shutting down WinApe.

If you want to check the loader program, you must set a break point
in &a054 in WinApe
run" disc
In &A0B8, a check is made to see if the sectors contains bytes &A6 or &A7

Conclusion:
Sector &79 is just is just a formatting or rather a deformation,
made to prevent copying of the disc with copy programs from that time.
With "Oddjob" you can make a copy of the disc
"Arkanoid (UK) (1987) [Original] A6 Disc has not been run.dsk"
but not of disc
"Arkanoid (UK) (1987) [Original] A7 Disc has been run.dsk"
So if sector &81-&88 contains files byte &A6, the disc has never been run
and if sector &81-&88 contains files byte &A7, the disc has been run

If anyone has a speedlock program from 1987 never ran I would like to see
what sector &79 and &81 contains or

If anyone can run "Arkanoid (UK) (1987) [Original] A6 Disc has not been run.dsk"
on a real amstrad machine and maybe confirm/deny that it is as I think.

You need WinApe to test.
Other emulators have problems with protection tab or the loader's format routine.

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[SerErris]

Interesting experiment. I will do that after my vacation (1 week). 

I can write a disk to a floppy via Kryoflux and then test it on a CPC. 

Luckily I can redo that over and over again :-)

[roudoudou]

obviously oddjob wont succeed copying this because this tool was not designed to handle strange formats

any badass copy tool will succeed (discology is still the best for that)

[Johnny Olsen]

Yes, but oddjob was not the point, but more used to illustrate the match
between copy programs and protection systems.The point is that maybe some
of the speedlock programs on the internet are not original versions.

If you follow the loader it checks if the filler byte in &81-&88 is &A6 or &A7
if it is =&A6 then sector &79 is formatted and the filler byte in sector &81-&88
changes to &A7. The next time you run the program it checks the sector &81-&88
if byte=&A7 then the loader run without formatting.

Here is my problem!! I can't test my theory because no emulators can run the
disc whose sector &81-&88 contains &A6.
WinApe's edit disc "Shift CTRL F1" shows that sector &79 is being formatted
but cannot save to disc.

If you have write protection tab enabled on the disc, it asks to turn it off,
why would it do that if it wasn't to write to the disc?

Thanks SerErris I'm looking forward to it.

[roudoudou]

programm wants you to unprotect floppy in case the protection fails => then it format the disc. Yep, it's violent

[roudoudou]

you can read an old article on cpc-archives (in french, use translation) https://www.cpc-power.com/cpcarchives/index.php?page=articles&num=196

[Johnny Olsen]

programm wants you to unprotect floppy in case the protection fails => then it format the disc. Yep, it's violent

Nope, the arkanoid Loader does the protection itself without rendering the game unusable. It does not format
the disc but only Sector &79. to protect itself from copying.

[roudoudou]

programm wants you to unprotect floppy in case the protection fails => then it format the disc. Yep, it's violent

Nope, the arkanoid Loader does the protection itself without rendering the game unusable. It does not format
the disc but only Sector &79. to protect itself from copying.

take a look at the link i mentionned, all the process is described and i just checked on arkanoid dump,

You may have some fun changing that #79 sector to size 2 => then the whole floppy is formatted right after displaying it's an illegal copy

that's why the programm ask for unprotecting floppy

[Johnny Olsen]

You are right, but I think we are starting from different starting points.
What Arkanoid disk did you check with and which emulator?
Does your disk in your test have a filler byte &A7 in sector &81-&88 and a damaged sector &79?

[roudoudou]

Yes, there is a #A7 filler but i insist, the sector is not read! you can put anything in that sector the protection will work fine (same thing for Supercycle which is supposed to contains real data => not read anyway)

There is a read command for #79 of size 2 => that sector should not exists (because it is size 0), the CPC read nothing and the protection is declared OK

The entire floppy is formated only if the ReadData #79 (of size 2) is successful. That will happend only with a crappy copy

[Johnny Olsen]

I'm just trying to figure out what's going on in the loader, not a test of which of us is right You cannot view this attachment.

In &A0D7 sector &82 is uploaded to &40 and in &A0F5 it is compared with &A6 and in &A0F9 it is
compared with &A7 So it doesn't matter what you put in those sectors!!!

[roudoudou]

what's going on in the loader is explained in the article i mentionned you only have to read it

you will understand that #A6/#A7 comparison