Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!leah!rpi!crdgw1!ge-dab!peora!tarpit!bilver!bill From: bill@bilver.UUCP (Bill Vermillion) Newsgroups: comp.sys.ibm.pc Subject: Re: How reliable are "hole-punched" 720K disks at 1.44 MEG??? Message-ID: <283@bilver.UUCP> Date: 22 Aug 89 04:51:13 GMT References: <1516@aws.cme.nbs.gov> <1811@garcon.cso.uiuc.edu> Reply-To: bill@.UUCP (Bill Vermillion) Distribution: na Organization: W. J. Vermillion, Winter Park, FL Lines: 50 In article <1811@garcon.cso.uiuc.edu> kubla@uiuc.edu (Kubla Khan) writes: >In article <1516@aws.cme.nbs.gov> durham@cme.nbs.gov (James H. Durham) writes: >>and, besides cosmetically, what >>are the differences between 1.44 and 720K disks? > >I don't know for sure, but were I to hazard a guess, I'd say the 720s were >1.44s that flunked the factory test procedures. > I wouldn't go around guessing about things like that. I can't find the specs for 3.5"HD disks, but essentially the differences as I understand them are similar to the differences between the standard 5.25" DS/DD diskettes and HD 5.25 diskettes. A standard 5.25" DS/DD has about a 300 oersted rating, and the HD has about 600 oersteds. A 3.5" DD has about 600 oersteds, and the HD (I believe) is higher, but I can't find the specs. The higher coercivity of the higher density disks means that you have to have a higher driving current to saturate the media. Using a low current on a high-coercivity diskette means that you don't record to the fullest and get lots of errors. Recording with a high drive current on a diskette meant for low current, will typically work on the outer tracks where the bit-density is lower, but as you go toward the center of the disk, the bit-density increases. With the low-coercivity diskettes you start getting self-erasure from the high current. This is why you get tracks locked out formating a 720k to 1.4 meg. The problem is that while the formatting is fresh and there is little magnetic decay you may get almost all the way through the disk. But as the disk ages you will be able to read less and less. With 3.5" DD's going for about 60 cents each, using two to get 1.4 meg seems a lot better than taking the chance of losing some important data. My time is worth a lot more than the 60 cents and gambling on lost data. I use REAL HD disks only to backup masters that came on HD, and use DSDD at 720k for archival. But then I think disks are so cheap. My first disks cost $4.50 each (heavily discounted) and we got 88k on them. (That was a few years before IBM made their first successful PC - there were a few tries before that fell flat!). -- Bill Vermillion - UUCP: {uiucuxc,hoptoad,petsd}!peora!tarpit!bilver!bill : bill@bilver.UUCP Please use either of the above in replies. The Reply To: may be bogus!