Call me crazy, but... storing data on audio cassettes =)

[Elledan]

This reminds me of my C64 days... loading games from a cassette

But seriously, how feasible would it be to use audio tapes (60/90 minutes) for storage, much like a tapedrive?

How much data would fit on one (90 min) tape? And with compression?

If enough data can fit on one tape, would it be possible to modify a cassette player so that it could record and 'play' faster?

Serial/parallel port or USB to connect the unit to the system?

--

Let me know what you think

 

[Moohooya]

Sure you could, but how much could you store on a tape? I believe the C64 used 300 baud. (Could be thinking of the modem.) I know the Spectrum was much faster, and the BBC also. They could have been as much as 1200 baud.

Looking at it from a theoretical point of view. Lets assume the tape's response is 20KHz. (Damn fine tape I believe.) The sample rate (20KHz) must be twice the highest bit rate, 10K/sec. So a 60 minute tape will store 10,000 * 60 * 60 = 34MB. However will need to break this up into blocks, each with its own preamble and CRC. You'd want a decent sized CRC so you could recover a number of lost bits. (Actually I believe there might be something better then CRC that HD's use that do a better job at recovering a sequence of lost bits rather which is more likely than a lost bit at the begining, one in the middle, and another at the end.) I'm sure if you look up the unformatted vs formatted disk capacities you'll get an idea of how much space goes to this. I'm going to assume a little over 10%, bringing down the tape to around 30MB. Now remember that the tape was assumed to have a responce of 20KHz, better than most. A more realistic number might bring down our final capacity to closer to 25MB. OK, if you use stero you could double this back up 50MB, still nothing stellar.

So yes, you can do it. However, I'd guess that even your smallest disk won't fit on all the audio cassettes you have in your house. (Unless you this fellow I knew once called Gus who had approx 1,000 metal cassettes.)

Now, if you changed this from an audio tape to a video tape, you'll get much more on. Don't know how much but I bet there is someone here who could do the math and give us a approx answer.

Moohoo

 

[Elledan]

Hmm... thanks for the extensive explanation!

25-50 MB? This makes me wonder: how is it possible that tapedrives fit many GBs on one tape?
In other words: what's the difference between an audio tape and a tape used with tapedrives?

I would also be very interested in hearing how much data a video tape could store.

 

[crypticlogin]

There's a reason why we've moved from loop media to disc, and that's for the efficiency in random access. There were a couple of attempts at VHS as a storage medium by using a video in/out card and piping encoded data out to a VCR to be recorded and played back. This had the whopping capacity of 150MB, pretty sizable at the time. But as we all know, recording and re-recording over consumer grade magnetic media like cassettes and videotape degrades the recording quality so after a while, archival quality takes a nosedive and you could lose data.

 

[Elledan]

tenchim,

yes, I'm aware of the degradation in quality after many write/read operations, but for backups this is hardly an issue. Neither is the slow access time of data on the tape.

By the way, 150 MB of data on a video tape? Even a (250 MB) Zipdrive can store more...

Hmm.... another question: how do Zip drives store so much data on a disk the same size as a floppy disk?

 

[NogginBoink]

<< This makes me wonder: how is it possible that tapedrives fit many GBs on one tape?
In other words: what's the difference between an audio tape and a tape used with tapedrives?
>>



I'm no expert, but the basic difference is that the media is designed to have more density. That is, you can store more data per unit of tape surface area on computer tapes.

This requires chemistry and smaller tape heads and all that jazz which makes it more expensive than audio tapes.

I also seem to remember someone using videotape for computer backup. Seems like it would work to me, as there is a huge amount of data in video pictures. But I also agree the number of rewrites is limited. After all, we can live with magnetic dropout on videotape (those white specks on the screen), but a computer backup would be useless with the same tap.

 

[Moohooya]

I think NogginBoink hit the nail on the head. A small drop in video or audio can be lived with. However if that was a whole block in your CRM database, you'd be a little pieved.

Compare the price of DAT media to an audio tape. Compare the price of a DAT drive to an audio recored. That explains why so much more can be stored on a DAT compared to an audio tape. Quality. Audio tape players have static head positions. A VCR has a dynamic head positon. It sweeps over the tape vertically many times per second as the tape moves slowly. I'm sure you could pack a huge amount on a video tape (I would have though up in the many GB range) but acess times would be terriable, and to have any sort of reliability you'd have to have a huge amount of data redundancy so you could piece back together the file if there were some bad blocks. I'd almost write every block twice, with perhaps a 1 second delay, to ensure the second block was nowhere near any physical damage that could happen to the first block. Ie, the blocks A-J would be
ABCDEAFBGCHDIEJFGHIJ

At a guess, data capacity for a 120 minute tape would be
120 * 60 * 25 * 50K (120 * 60 seconds * 25 frames per sec * 50K per frame) = 9G
But then, CRC, preamble, format, data duplication and all of a sudden we are down to 3-4G

Moohoo

 

[Elledan]

<< I'm no expert, but the basic difference is that the media is designed to have more density. That is, you can store more data per unit of tape surface area on computer tapes. >>


As I suspected

Thanks for the explanations, NogginBoink and Moohooya!

BTW, what does the average tapedrive & media cost, and which different types of tapedrives (DAT etc.) are there?

 

[Jerboy]

<< There's a reason why we've moved from loop media to disc, and that's for the efficiency in random access. There were a couple of attempts at VHS as a storage medium by using a video in/out card and piping encoded data out to a VCR to be recorded and played back. This had the whopping capacity of 150MB, pretty sizable at the time. . >>



Yet zip 250MB can't store anything remotely close to six hours worth of VHS EP quality video with hi-fi stereo audio.

 

[Elledan]

<<

<< There's a reason why we've moved from loop media to disc, and that's for the efficiency in random access. There were a couple of attempts at VHS as a storage medium by using a video in/out card and piping encoded data out to a VCR to be recorded and played back. This had the whopping capacity of 150MB, pretty sizable at the time. . >>



Yet zip 250MB can't store anything remotely close to six hours worth of VHS EP quality video with hi-fi stereo audio. >>

True. That's also one thing I don't understand. Could you explain it?

 

[Sunner]

There was a company selling a device that would allow you to backup data to VHS tapes.

I believe the max capacity was 1.5 GB of data, I dont know what tape size/compression was used to achieve that though.

 

[SCSIRAID]

Your plain ole audio tape has 4 tracks on it. 2 in one direction and flip the tape and get two in the other direction. Some computer tape drives use a helical scan mechanism which writes very thin tracks 'sideways' on the tape. The helical scan increases the data rate and the thin tracks increases the capacity/density. Other computer tape drives use higher transport speeds and lots of very thin tracks. Listen to your Travan drive and notice the little 'whirrs' like a car starter every few minutes. That is the drive moving the head to a new track and reversing direction. You could do this kind of thing with an audio tape if you had a special transport but its not wide enough to put a lot of tracks on.

 

[Elledan]

Thank you, SCSIRAID! I think I understand it now