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Conrad
Registered: Nov 2006
Posts: 833 |
Efficient use of sectors on 1541 disks.
A question/idea(?) to loader-coders...
I've been curious on how the .prg file structure is laid out on a standard 1541 floppy disk, particularly on sector use.
Sometimes you always get a sector with completely wasted bytes - for example, if a program's last sector from a chain only needs about 8 bytes of memory (plus the first 2 for end marker and number of bytes left), that means the other 246 bytes are wasted, that could of been used by another small program.
I'm not too sure if anyone has actually written a loader which does this, but a nice idea would be to have an offset parameter value stored somewhere in the directory sector for each file. Reading this up in some 1541 manual, Byte locations #22-#25 in a directory file structure are known as unused. These could be used to store the offset values, which shouldn't really harm the directory at all. The only problem would be that the standard kernal loader may bring back errors due to ignoring these particular locations and then possibility of loading corrupted data into memory. Only loaders coded by us could do this job.
The last few days I've been learning about drive coding and I never knew how much control you can have with the 1541's memory :) It's early days for me yet, but soon I'll understand more and then give this idea a try.
If anyone has thought about this idea before, I would really appreciate their opinion :)
Thanks.
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Burglar
Registered: Dec 2004
Posts: 1033 |
you mean iffl ;) |
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Oswald
Registered: Apr 2002
Posts: 5025 |
yeah this was already done in various implementations, generally it is called iffl, and usually used for storing cracked game data.
btw this is a common problem with modern filesystems aswell AFAIK, but the storage capacity seems to be growing fast enough, to make it a minor issue. |
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Steppe
Registered: Jan 2002
Posts: 1510 |
Oswald, you're right. Back then my disks used to have 664 blocks free. Nowadays, with storage capacity growing rapidly, I can without problem save 700-730 blocks onto it. They call it oversaving, hehe. |
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Conrad
Registered: Nov 2006
Posts: 833 |
I see,
Well, since there are now better file/disk systems already invented, I guess this won't be a worry after all :) yet I may give this idea a go sometime - for good old standard 644 block disks :).
Thanks for your input guys :) |
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Oswald
Registered: Apr 2002
Posts: 5025 |
you can also use the directory track to store data, track 18 in default is fully reserved for the dir. |
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Steppe
Registered: Jan 2002
Posts: 1510 |
But joking aside, isn't there an IFFL rant over at covertbitops.c64.org? |
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Oswald
Registered: Apr 2002
Posts: 5025 |
IIRC there is |
