DEFMTH4.CVP 920105 Write protection - hardware Generally, in the microcomputer world, write protection is held to mean write protection implemented by hardware. Although it is a truism that "whatever the hardware people can do, the software people can emulate, and whatever the software people can do the hardware people can emulate", it is physically impossible to overcome a "sufficient" hardware protection with software. Note, however, that not all hardware protection devices are as safe as they may seem at first glance. First, the universal write protect "tab" on floppy disks. It *is* possible to write to *some* write protected drives. Certain systems (MS-DOS is not one) check for write protection in software rather than hardware. Thus, even though the write protect device is hardware, the software checking can be circumvented by a virus. (In systems where the write protection *is* effective, it is still the case that the notification of an attempt to write to the drive is done through software, and so the warning that something may be going on may be trapped by the virus. However, even on some MS-DOS systems, write protection may not be reliable. Some manufacturers use an optical, rather than mechanical, sensor for the write protect tab or notch. Using "translucent" floppy disks, the "silvered" write protect tabs or even the shiny black ones on 5 1/4" diskettes, may allow sufficient light to get through to the sensor as to leave the disk unprotected. It is interesting to note that, because of the two different protect tab designs, the hardware write protection circuits for 5 1/4" diskettes generally "fail safe" in a write disabled configuration, whereas 3 1/2" diskette drives "fail" into a writable configuration. (A pity. I prefer the ability to protect and enable repeatedly without building up gobs of tape adhesive around the notch. And when I did protect 5 1/4s, I used to use "magic" tape as it was easier to remove. These days I'm using "Post-it" notes ...) As in the past, so again I will deplore the failure of drive manufacturers to provide write protect switches on "fixed media" hard drives. Tape and cartridge media do have tabs or switches. Those knowledgeable about hardware and drive cabling can "retrofit" switches, but recent tests at various sites with hardware write protect switches have indicated problems with certain types of drives. No one procedure has been proposed that works for all types of drives. copyright Robert M. Slade, 1992 DEFMTH4.CVP 920105 ============== Vancouver ROBERTS@decus.ca | "My son, beware ... of the Institute for Robert_Slade@sfu.ca | making of books there is Research into rslade@cue.bc.ca | no end, and much study is User p1@CyberStore.ca | a weariness of the flesh." Security Canada V7K 2G6 | Ecclesiastes 12:12