And then there is the problem of Media differences, as mentioned before by someone else on the list, but got it backwards, the HD disk has a thinner magnetic coating, and smaller magnetic particles. The thinner coating means that the magnetic force needed to alter the particles is much less than an 800k drive puts out for the 800k disks. The smaller particles allow data to be packed more tightly on the HD disks, this helps the HD disks able to have 18 sectors per track. Also the tracks on a 1.4 HD disk are thinner, and the sectors are longer.
This info is from the book "Inside The Apple Macintosh" written by Jim Heid and Peter Norton, copyright 1989 Dan M. Dan, a message I beat into my students is: don't believe everything you read, just because it's in a book! Consider the qualifications of the authors; no one is an expert in everything. And consider logic, too. So, thanks for giving me a chance to point out this book's error. Those authors you cite are just plain wrong. It is well known among disk designers that you need to INCREASE the specific magnetic strength of particles as you shrink the bit size, to prevent excessive diminution of signal strength (simple logic: smaller bits are weaker magnets unless you do something about the material properties). If you do some more careful research, you'll find that the coercivities of media have indeed increased with each generation as densities have gone up. The original information I posted, including the specific coercivity values I cited, were correct. The data you cite about rotation rates is interesting, but ultimately irrelevant. The bits switch magnetizations so fast (nanosecond scale) that rotation speed has no practical implications at all (other than wear). The only things that really matter are the remanent magnetizations of the particles, the track width, and the bit density. If you're going to pack more bits along a track, the bits will be smaller. Again, if you don't want the read signal to go down, you've got to make the magnets more powerful. That necessarily implies that the coercivities must increase, so they're harder to write. Hope that makes this clear. -- Prof. Thomas H. Lee Center for Integrated Systems, CIS-205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 http://www-smirc.stanford.edu 650-725-3709 voice, -3383 fax -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ . -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> The FAQ: <http://macfaq.org/> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
