lauren@vortex.COM (Lauren Weinstein) (11/12/90)
All other arguments aside for the moment, it would appear that with helical scan, timing track-based technologies, the narrower the tape, the more precise the required mechanical tolerances, and so the greater the required manufacturing and operational precision. In the pro-audio world, where there has been considerable experience with DAT for quite sometime now, problems with tape interchange and replayability, purely due to variations in mechanical tolerances, have been nagging problems. Sometimes these problems are immediately apparent with and between particular machines, and sometimes they only appear as the equipment (and tapes) age. There have been other problems as well, such as serious tape dropouts in some cases (this latter problem may often be related to particular brands of tape, but many studios now run dual DATs for protection in any case). While a robust ECC system makes tape dropouts of less concern, it's still worth noting. So while comparing the features and cost-competitiveness of the 8mm/Exabyte vs. 4mm/DAT world, it's probably worth remembering that as the tape gets tinier, the required mechanical precision that needs to be maintained becomes considerably greater, with all that implies. --Lauren--
kev@hpcpbla.HP.COM (Kevin Jones) (11/14/90)
There is a degree of truth in the interchange and replayability "nagging problems". Mechanical aligments of drives (normally from different vendors) can result in data being recorded at slightly different azimuths. AT HP, we did a considerable amount of interchange testing with our 1st generation of DAT products, and found that there was no problem. We have also done interchange tests between our drives and drives of other DAT vendors and have not noticed any problems. DAT drives used for data storage (as opposed to Audio) have a major advantage in that they can RETRY in the case of an error. If a slightly misaligned tape is read by a DAT (computer) drive then you will see some "recovered" errors. A slightly misaligned DAT (audio) drive CANNOT DO RETRIES (unless you're prepared to have Beethoven's V'th interrupted repetitively :-), therefore a failure to recover data on "1st pass" is an unrecoverable error. > There have been other problems as well, such as serious tape dropouts Tape droputs DO EXIST. > this latter problem may often be related to particular brands of tape All tapes have "blank spots", where the coating of magnetic particles on the media is deficient. Some have it more than others. The good news however is that the majority of these dropouts are manufacturing defects. Any tape drive with READ-AFTER-WRITE will detect that it just wrote data over a dropout, and will rewrite that data until it detects it has placed a perfect copy of that data on tape. Dropouts for computer tape drives with read-after-write are therefore a non-problem. (PS. All HP's DAT drives implement read-after-write). The audio world is worse off than the computer world when it comes to dropouts. A sound recording needs a constant data rate. An audio DAT recorder will not do read-after-write, and even if it did, then it couldn't take "time off" to rewrite data, since it would get "out of synch" with the music it was trying to record. ----------------------------------------------------------------- Kevin Jones. | Hewlett Packard Ltd, | Computer Peripherals Bristol, kev%hpcpbla@hplb.hpl.hp.com | Filton Road, | Stoke Gifford, Tel: 011 44 272 799910 (ext 22351) | Bristol. BS12 6QZ. | ENGLAND. ----------------------------------------------------------------- This response does not represent the official position of, or statement by, the Hewlett-Packard Company. The above data is provided for informational purposes only. It is supplied without warranty of any kind.