henkp@nikhefk.UUCP (Henk Peek) (02/16/88)
In article <1673@mipos3.intel.com> dbraun@cadev4.UUCP (Doug Braun ~) writes: ->In article <20291@amdcad.AMD.COM> philip@amdcad.UUCP (Philip Freidin) writes: ->>In article <990@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes: ->>> ->>>I have read several times and have seen discussed on this network, ->>>a phenomenon referred to as sector creep. Apparently, sector creep ->>>is a cumulative phenomenon that causes disk data errors after ->>>extended time has passed. ->> ->I looked at schematics for a (Shugart 10 meg) winchester, and I ->noticed something interesting. This drive, and most smaller, cheaper ->winchesters, use diodes to switch the heads. Each head is center-tapped, ->and a positive voltage is applied to the center tap to forward-bias ->diodes that run from the end-taps on the heads to the preamp inputs. ->The circuit looks like this: -> -> ________ -> --------------->|------+---| | -> ( | | | -> ||| ( other head ->|--' | | -> ||| ( | | ->head ||| (------- +V | preamp|------------ ->coil ||| ( | | -> ||| ( | | -> ( | | -> --------------->|------+---| | -> | | | -> other head ->|--' -------- -> ->The point is that to forward bias the diodes, there must ->be a dc current running through the heads at all times. ->This would produce some magnetic field. Normally those two currents have the same value. Both currents generating a magnetic field in the head. Only the direction of both fields is not the same. The sum of the two magnetic fields is nearly zero. The write system uses the same system. Only the two currents are modulated by the write bit stream to different values. Those different currents does not fully compensate and generate the magnetic write field. ->Doug Braun Intel Corp CAD -> 408 496-5939 -> -> / decwrl \ -> | hplabs | ->-| oliveb |- !intelca!mipos3!cadev4!dbraun -> | amd | -> \ qantel / Is this an another undocumentated mode to get a write only harddisk? :-) Henk Peek ..uunet!mcvax!nikhefk!henkp