Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!netnews.upenn.edu!vax1.cc.lehigh.edu!cert.sei.cmu.edu!krvw From: PHYS169@csc.canterbury.ac.nz (Mark Aitchison, U of Canty; Physics) Newsgroups: comp.virus Subject: Re: can we trust diskette write-protection? (PC) Message-ID: <0005.9105011240.AA25914@ubu.cert.sei.cmu.edu> Date: 30 Apr 91 00:11:00 GMT Sender: Virus Discussion List Lines: 25 Approved: krvw@sei.cmu.edu jim@cavebear.berkeley.edu (Jim Bradley) writes: > I write-protected each with a silver sticker from another box of diskettes. > I subsequently discovered that I could *freely* write or erase files from > any of these "write-protected" diskettes in the 1.2M half-height floppy drive > of an AT-clone or in the retro-fit 360K half-height floppy drive of an IBM XT . > > Both machines are located in a computer lab I manage. I used to trust write-protect tabs until very recently. My main advice is: DON'T! Possibly, the reason why it sometimes fails, other than obvious loose wires, is because of light bouncing around the diskette drive. Remember, a tab over the notch should stop the light getting to the photo-detector on the other side; if it can bounce of a silvery tab, onto metalwork, and onto the detector, it is like having no tab on at all. I haven't tested my theory, but I suspect black tabs are better, and there should be little distance between the diskette and the photo-transistor or whatever. Someone may be able to answer the question as to whether the circuitry uses synchronised pulsed light, or plain light (the latter would mean daylight from outside the computer could nullify the protection system). Mark Aitchison.