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johncl
Registered: Aug 2007
Posts: 37 |
Turbo Tape, how does it work?
I have always been curious about how turbo tape really worked. I know that the tape drive originally could only read 50 bytes per second which would take a whopping 21 minutes to fill up the whole memory. I was always under the impression that games used compression to speed up tape loading (Just did a test with Giana Sisters which took 4 minutes to load).
Did Turbo Tape fiddle with the speed that data was written and read to the tape? I didnt think that was possible (only thought that was how they sped up disk reading/writing). If anyone got a good resource at how e.g. the well known Turbo Tape works, please post a linky here. |
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tlr
Registered: Sep 2003
Posts: 1790 |
Quote: As did I. It's just that a GCR encoded byte needs two extra bits, so a worst-case turbo-tape with 50% ones should just about break even with it.
At least, I think that's how it works out..
Hmm, yes you are right.
I assumed a '1'-bit was twice as long as a '0'-bit, but now I realize the difference is much less.
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enthusi
Registered: May 2004
Posts: 677 |
check neoload for a error-correction loader.
The most complex there is so far.
Neoload |
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tlr
Registered: Sep 2003
Posts: 1790 |
Yes, noted that before. Very cool!
The discussion about GCR was an attempt to propose a faster loader than turbo tape though.
Perhaps it is already close to max? Very cool in that case as it is from 1983. :) |
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Frantic
Registered: Mar 2003
Posts: 1648 |
The loader in Deep Throat by Durex uses four pulse lenghts corresponding to 00, 01, 10, and 11. This minimizes the constant minimal length you always need to have in a pulse. I think there was also a fifth pulse length, signalling "syncrhonization point", since you can ffwd and rewind the tape while the demo is playing, but still resync at regular intervalls...
Greetings too Krill! (...and greetings to everyone from the Polish/German border..;) |
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johncl
Registered: Aug 2007
Posts: 37 |
Ahh, thanks for clearing that out. I didnt know you had such a low level access to the tape read/write mechanisms that enables you to actually time pulses.
So to further discuss this, what did most commercial games use? For example Novaload which I know a number of distributors used. I guess they couldnt squeeze it as low as Turbo Tape as that would probably have ended up with the game not working on some tape drives (and couldnt handle any kind of error).
You see, I am quite surprised at the fact that close to 100% of the old tapes I have tried still load perfectly after 20-25 years of storage (and I mean all sorts of storage since these are bought from around the world). In fact, only one tape has bugged out on me in which the tape drive was not even able pull the tape after 3 count ticks into the tape start. :) |
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Martin Piper
Registered: Nov 2007
Posts: 722 |
Cyberload/Novaload etc don't handle the potential for the really slow or fast tape drive wobblyness so I suppose it was never much of an issue. Basically, don't bother writing code to calibrate the timings because they're not that much of an issue compared to the cycle timing wobbles you can get when displaying a picture during loading.
Unless you have the screen turned off and want to make a really fast loader. But in my experience the time differences you can get on a real C2N during loading change due to the amount of tape on each spool. Or if the pet dog walks past the C2N. :) |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
I believe that much faster turbo tape formats are possible. The main problem with the existing fast tape stuff is, that those routines always use hardcoded thresholds for 0 and 1. This causes problems if you move from one tape drive to the next so the threshold has to be chosen in such a way that the 0 and 1 ranges are quite big. If you manage to measure the tape drive speed first, you might be able to use much smaller pulse lengths -> faster loading + more data on a tape.
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algorithm
Registered: May 2002
Posts: 705 |
There was the SuperTurbo format which was used in the Action Replay Cartridge which i believe was nearly twice as fast as Turbotape. I dont think there was any other loader which would load data this fast commercially but that is understandable as it could have caused more possibility of error |
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Martin Piper
Registered: Nov 2007
Posts: 722 |
Re: Action Replay super turbo. If the assumption is made that the C2N doing the saving is going to be the C2N that will be doing the loading then it's possible to make the bit rate quicker without any fancy timing calibration. :) |
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johncl
Registered: Aug 2007
Posts: 37 |
Hm, did any of these fast loaders/savers do real time compression/decompression of data? E.g. RLE compression? |
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