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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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algorithm
Registered: May 2002
Posts: 705 |
Quote: Well, there are some Mastertronic tape titles that does have a minigame in front of it. Invade-A-Load was one of them and I remember its on the Rogue game at least. What I find interesting is that many games had fullscreen bitmap pictures that you could see while it was drawing on the screen, basically adding another 20-30 second to the loading time. :)
Of course it was cool back then as you got tired of staring at a blank screen. When loaders came with Galway music pumping out the mono speakers we never wanted to go back. :)
Just surprising that more was not done with it. After all. the IRQ is responsible for the loading and outside of this, it would have been possible for anything to run without distracting the loading at all unless you wanted solid rasters which would mean more complex tape mastering |
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AlexC
Registered: Jan 2008
Posts: 299 |
Quote: Just surprising that more was not done with it. After all. the IRQ is responsible for the loading and outside of this, it would have been possible for anything to run without distracting the loading at all unless you wanted solid rasters which would mean more complex tape mastering
The reason is simple - 1541 came ;) But actually Datassette is one of interesting devices because it's capabilities to store huge amount of data (comparing to 1541) and technical details has been almost forgotten even if it looks simple. There are very few technical documents regarding this device unfortunately. I've learned a lot about it studying Cyberload. |
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algorithm
Registered: May 2002
Posts: 705 |
Tape mastering (eg saving/loading) is very simple. just precise timing and writing values to a location at precise intervals ( i think its memory location 01?) then the loader can be interrupt driven (provided it runs at full priority) to pick up the bits of data saved to tape. The secret is how to place the 0's and 1's. as well as delay timing. As long as the interrupt routine reads all the data, then exits (to allow main loop to execute whatever) and gets back to the interrupt before the next bit appears on tape etc. Anything can occur in the main loop
Although sprites and the screen on can cause problems if the data is more densely packed |
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Martin Piper
Registered: Nov 2007
Posts: 722 |
Multiplexor while tape loading... Hmm...
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enthusi
Registered: May 2004
Posts: 677 |
check this for precise timing on IRQ tape load :)
A Load of TAP
...what a nice thread... :) |
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johncl
Registered: Aug 2007
Posts: 37 |
Yeah, thats a pretty nice demo showing tape-streaming. I am quite sure there are lots of cool things one could do with it. Still, a scroller is pretty cpu consuming so obviously perfect timing is necessary to be able to use this for example a game or something. Although I guess one would be bored at rewinding the tape for every time one wanted to play again. :)
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Mace
Registered: May 2002
Posts: 1799 |
Quote:Although I guess one would be bored at rewinding the tape for every time one wanted to play again. :) That is easily fixed by putting the demo on both sides of the tape ;) |
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algorithm
Registered: May 2002
Posts: 705 |
Quote: Quote:Although I guess one would be bored at rewinding the tape for every time one wanted to play again. :) That is easily fixed by putting the demo on both sides of the tape ;)
Or make the demo two sided :-} |
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johncl
Registered: Aug 2007
Posts: 37 |
What I find strange is that they didnt see the potential of the tape drive better. For example, from what I have understood, these tape drives only recorded one track, while most heads actually supported stereo tracks. Why didnt they record on both tracks which could bring the saving/loading down to half. And while they were at it they could have recorded both "sides" at the same time which would make it 4 times faster. Although that would require the user to always put the tape on the correct side since they would still use the standard tape drive.
I guess it was because they could reuse existing hardware to make it as cheap as possible and once it was established there was no way they could change it. Sad really, imagine tape games loading 4 times faster. |
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algorithm
Registered: May 2002
Posts: 705 |
Quote: What I find strange is that they didnt see the potential of the tape drive better. For example, from what I have understood, these tape drives only recorded one track, while most heads actually supported stereo tracks. Why didnt they record on both tracks which could bring the saving/loading down to half. And while they were at it they could have recorded both "sides" at the same time which would make it 4 times faster. Although that would require the user to always put the tape on the correct side since they would still use the standard tape drive.
I guess it was because they could reuse existing hardware to make it as cheap as possible and once it was established there was no way they could change it. Sad really, imagine tape games loading 4 times faster.
Thats almost the same question as asking why VIC II did not have 16 sprites rather than 8. I suppose a mono signal is more reliable and 'lasts' longer. Besides if the tape drive had the facility along with the rest of the circuitry for the C64 to be able to read two signals, not many people would have purchased the 1541 (Although Random Access is always great)
The only advantage in the tape drive was its storage capacity in comparison to the disk as well as the cheap price. |
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