Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site aesat.UUCP Path: utzoo!aesat!bmw From: bmw@aesat.UUCP (Bruce Walker) Newsgroups: net.micro Subject: Re: Erasing Disks Message-ID: <359@aesat.UUCP> Date: Thu, 14-Mar-85 08:38:26 EST Article-I.D.: aesat.359 Posted: Thu Mar 14 08:38:26 1985 Date-Received: Thu, 14-Mar-85 08:57:49 EST References: <1960@sdcc6.UUCP> <736@ihnp4.UUCP> Reply-To: bmw@aesat.UUCP (Bruce Walker) Organization: AES Data Inc., Mississauga Ont., Canada Lines: 55 Summary: don't bother [Quotes edited:] >> I had seen ads advertising a device to erase floppy disks much as a >> tape eraser works on cassettes. [ ...... ] Can disk life REALLY be >> extended by periodic erasing? > >It is funny that you mention this. Last night I was talking with a DEC >c.e. concerning floppy disks on a PDP 11/23+. One of the comments that >he made was that if a bulk eraser is used on a floppy for that system, >servo (head) positioning data is lost on the floppy, and the disk is >totally useless. > >Of course, we were talking about one specific system, and one type of >drive (the RX02). These comments may not apply to a 5 1/4 inch drive >on a PC, but do you want to experiment? > > jeff williams > ihnp4!cfiaime These (last) comments definitely do NOT apply to the PC, or almost any other 8 inch or 5.25 inch floppy disk system I've heard of. The new Drivetec 5.25" high capacity drives (3 Mbytes or something) use embedded servo info and those floppies need factory formatting, but most other drives use open-loop step motor positioners which couldn't care less about what's recorded on the media. I am not going to conjecture about whether diskette life can be extended but I don't feel that the average user will derive any benefits from bulk erasing his disks. *If* your heads became magnetized for some reason, you would want to demagnetize the heads and possibly bulk erase disks to prevent that from reoccurring, but that is rare. While designing disk controllers and analog read/write channels, I found that bulk erasing was useful to improve the signal-to-noise ratio for critical measurements but that was for a very specific task that shouldn't really affect normal disk operations. The trouble I can forsee with casual bulk erasing is that you have to be very careful about using the eraser or you will leave a strong magnetic "residue" on the diskette which could magnetize the heads. Should this occur, you will gradually erase the magnetic domains on each diskette you use in the affected drive. If you still want to try it, you can use a "standard" cassette/reel tape eraser such as Radio Schlock sells for under $20 and read the instructions and follow them very closely. They advise you to make sure that the eraser is several feet away from the object you wish to erase when you turn it on and keep the eraser moving in slow circles while it is on. The object of all this arm- waving is to avoid any left-over magnetic field which could be caused by the eraser's coil being ener/de-ener/gised while the 60Hz AC voltage is greater than zero and the coil is near your object. Another caveat: make sure that your DOS has a "true" disk format command before you erase any diskettes. The old DEC Rainbow didn't, but one could obtain a public-domain version from some RCP/M systems. Bruce Walker {allegra,ihnp4,linus,decvax}!utzoo!aesat!bmw