Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!spool.mu.edu!uwm.edu!linac!att!cbnewsj!jwi From: jwi@cbnewsj.att.com (Jim Winer @ AT&T, Middletown, NJ) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Diffs between DD & HD disks Summary: Yes, Virginia, there is a difference. Message-ID: <1991Apr9.164631.23646@cbnewsj.att.com> Date: 9 Apr 91 16:46:31 GMT Article-I.D.: cbnewsj.1991Apr9.164631.23646 References: <1991Apr6.234019.2894@agate.berkeley.edu> <1991Apr8.180820.2132@unixg.ubc.ca> Distribution: usa Organization: AT&T Bell Laboratories Lines: 34 In article sigma@sun.ipl.rpi.edu (Kevin Martin) writes: > > Can someone with technical references or an inside on the topic please > clear up the issue of whether or not there is a difference in the media > between DD 3.5" and HD 3.5" disks? Answers from both sides have rarely > been more complex than "yes they are" "no they aren't" "so's your mother" > and I'd also like to be sure someone isn't confusing this question with the > same questions about 5.25" disks or memory chips or what-have-you... The difference is 600 (dd) vs 700 (hd) oested (sp?) in magnetic coercivity. Unfortunately, I can't find my file that I have used the last couple of times, so here is a quicky. 1) DD drive doesn't write well on HD disk, drive's magnetic field is not strong enough to change the disk reliably. DD's are *not* HD's that failed -- HD's dont work well in DD only drives. 2) Writing HD on a DD disk is likely to result in bits flipping. Three bits: 1,0,1 are twice as close togehter on HD as DD. Since DD takes less magnetic force to flip, middle bit is more likely to flip. At DD density, bits are farther apart and less likely to flip. 3) There is no free lunch. 4) Your milage may vary. Probably, some manufacturers cheat. Jim Winer -- jwi@mtfme.att.com -- Opinions not represent employer. ------------------------------------------------------------------ "The change (due to distance from the center of the earth) in the acceleration due to gravity is trivial for dropping cats from high buildings or airplanes, but must be taken into account when launching them from satellites or far planets." Bill Schulz