Re: Weak Bits

From: Armin Vogl (
Date: 2007-12-04 23:23:07

Hi Pete,

I read the infos on your page. I still have a few questions:

>We mentioned before that if the drive gets more than two '0' bits in a row, 
>it clocks in a random '1' bit occasionally.

Is it really random ? I mean the 74LS193 is not reset by the BIT_SYNC line 
in case there are more than two "0" in a row. Is it the variation in 
rotation speed together with variation in the decoder clock which creates 
different bytes for each rotation ? The decoder clock defines the "width" of 
the bit in time and clocks the 74LS193. Would it be enough to have a number 
of bits on the track that can not be divided by 8 to generate a pattern that 
changes with each rotation ? This would still not be random, because after a 
"1" bit is read, the byte that will be read only depends on how long you get 
"0" bits. But this patternis not random. I think it would look like random 
if the amount of bits on the track can not be divided by 8.

So the question is: does G64 support an amount of bits on a track rather 
than bytes ?

I still don't get what is "weak" about the bits. I don't understand the term 
"weak bit". It is not that the bits themselves are not stable on the 
magnetic medium, but it is more that the drive electronics reads a different 
byte for each rotation, or ?

Sorry if I ask questions that have already been answered elsewhere, but I 
couldn't find a detailed explanation on the web.


----- Original Message ----- 
From: "Pete Rittwage" <>
To: <>
Sent: Tuesday, December 04, 2007 10:49 PM
Subject: Re: Weak Bits

>> Hi !
>> I would like to know more about weak bits. What are weak bits ? How can
>> they
>> be stored in the
>> GCR file format ? what would be necessary to support weak bits if you 
>> want
>> to emulate the r/w
>> head for drive emulation ?
> There is a page on my site detailing most styles of copy protection used
> on the C64.  Check under the "weak bits" section (but read the rest for
> background information)
> -
> Pete Rittwage
> C64 Preservation Project
>       Message was sent through the cbm-hackers mailing list 

       Message was sent through the cbm-hackers mailing list

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