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Disassembly of the 3 boot sectors?


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#1 Larry OFFLINE  

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Posted Tue Apr 23, 2019 3:09 AM

Does anyone have a well-commented disassembly of the boot sectors?  I got to thinking about this as a result of the "disk/ATR sorting thread."

 

Thanks!



#2 Rybags ONLINE  

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Posted Tue Apr 23, 2019 3:30 AM

The book "Inside Atari DOS" has source code which is relevant to Dos 2.5

 

Note that a particular Dos could have a vastly different boot sector than another and the only fixed architecture in the boot sector is the first 6 bytes and the "boot continuation code" that commences at the 7th.

 

The flags relating to enabled drives/buffers might be the same in other Doses but there's no requirement for them to be.

 

A fresh formatted disk should have 3 boot sectors under Dos 2.x which has the boot continuation code which IIRC looks for and loads DOS.SYS.

There are some Doses that will issue their own boot error text if the required Dos system file/s aren't present.



#3 Larry OFFLINE  

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Posted Tue Apr 23, 2019 3:45 AM

Thanks, I have an original of that book.  Didn't think to look there!



#4 Rybags ONLINE  

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Posted Tue Apr 23, 2019 4:00 AM

There's also a standalone Dos 2.0S source code that's floating around.

 

I got a copy in the day and I think it predates the book.  Not sure if it offers anything extra in the way of comments and there's no accompanying extra info with it.

Don't seem to have it in file form but it might be on the 'net somewhere.



#5 sup8pdct OFFLINE  

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Posted Wed Apr 24, 2019 4:33 AM

It all depends on what is being booted. There is a byte in the 1st 6 that tells the os how many sectors to read in before passing to the code contained in the boot sector /s.

Most doses load 3 before jumping to code loaded from said 3 sectors. Games can be any value starting from 1 through to 255.

 

James






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