Xref: utzoo comp.periphs:2269 comp.unix.questions:17606 Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!bloom-beacon!gatech!dscatl!galbp!wittsend.lbp.harris.com!mhw From: mhw@wittsend.lbp.harris.com (Michael H. Warfield (Mike)) Newsgroups: comp.periphs,comp.unix.questions Subject: Re: Cartridge tape questions Keywords: QIC tape cartridge Message-ID: <9031@galbp.LBP.HARRIS.COM> Date: 7 Nov 89 21:32:53 GMT References: <169@iquery.UUCP> <9633@june.cs.washington.edu> <1989Oct30.220321.25394@chx400.switch.ch> <9638@june.cs.washington.edu> Sender: news@galbp.LBP.HARRIS.COM Reply-To: mhw@wittsend.UUCP (Michael H. Warfield (Mike)) Followup-To: comp.periphs Organization: Lanier Network Knitting Circle - Thaumaturgy & Speculums Division Lines: 59 In article <9638@june.cs.washington.edu> witold@june.cs.washington.edu (Witold Paluszynski) writes: >Oh, pardon me for not making myself more clear. When I said the >9 track drives were compatible I meant that the COMPATIBLE drives >were compatible. Sure you can buy an incompatible drive. But >you can also buy a compatible one. No such luck with QIC. The example with the 9 track drives though is not a good one. The difference in density was in the frpi (flux reversals per inch). The difference in the QIC formats is in tpi (tracks per inch). The newer format involves a higher track density that effectively doubles the data on the tape (60 Meg tapes record 120Meg). In order to get to 150Meg, different tapes are used that also support a higher frpi as well as tpi. The problem is that the technology, in this case, is not really downward compatible when you change the tpi. To increase the tpi you have to use thinner heads. Now thinner heads can read the wide tracks of the old format just fine. However, if you were to record the old track density with the newer head geometry, you get thinner tracks spaced out with wide gaps between them that have not been erased or recorded on. The thinner tracks result in a MUCH lower signal level on the older heads and the gaps between the tracks introduce noise (or worse extranious unerased data) into the playback system. The result is that the old heads cannot read the thinner tracks. This is a physical limitation resulting from the thinner tracks. The only way around it is not to use the thinner tracks. Which means you don't use this technology. So to get the advantage of THIS technology you sacrifice some compatibility. A closer analogy with the large tapes would not be the difference between 800 bpi and 1600 bpi but rather between 7 track tapes (How old are you? Am I showing MY age :-) :-) ) and 9 track tapes. Yes there were some strange animals that could support both, but only by having two complete head assemblies. Most of the time it was wiser to just keep one old clunker around for the 7 track tapes after upgrading to 9 track tapes. Some places couldn't even justify that after a while and just farmed out their 7 track tapes to outside vendors who specialized in conversions. A comparible situation currently exists in the MS-DOS world. The 1.2Meg 5 1/4" floppy disks are records at 96tpi. The older 360K disk are recorded at 48tpi. It is a simple matter for the 1.2Meg drives to read the 360K format. You can format and record the 360K format on the 1.2 Meg drives but the chances of it being readable on a 360K drive is very slim. In contrast the 3 1/2" floppy drives use a different recording density between the 1.44Meg and the 720K formats. For this reason the 1.44Meg drives are fully capable of reading and writing the 720K disks just by changing the data transfer rate. The resulting disks are identical to a disk recorded on a 720K drive. The difference in the head geometry on the new high capacity tape drives means it is physically incapable of recording a tape that is identical to a tape recorded by an old drive. It is then difficult to expect the old drive to be able to read that tape. The fact that the manufactures do not enable this type of action is purely defensive. I certainly would not want to deal with the volume of customer complaints that would result when the old drives fail miserably trying to read a tape from a new drive. Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw (404) 270-2123 / 270-2098 | mhw@wittsend.LBP.HARRIS.COM An optimist believes we live in the best of all possible worlds. A pessimist is sure of it!