Xref: utzoo comp.sys.ibm.pc.misc:9728 comp.sys.ibm.pc.hardware:8864 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!gatech!mcnc!rti!mozart!sasgig From: sasgig@unx.sas.com (Greg Grimes) Newsgroups: comp.sys.ibm.pc.misc,comp.sys.ibm.pc.hardware Subject: Re: Floppy disk questions Message-ID: <1991May21.143446.20087@unx.sas.com> Date: 21 May 91 14:34:46 GMT References: <1991May18.163148.1048@husc3.harvard.edu> <1991May20.175056.24786@unx.sas.com> Organization: Anonymous UNIX Generic Hackers (AUGH) Lines: 43 In another article, gurganus@stable.ecn.purdue.edu (James P Gurganus) writes: >sasgig@unx.sas.com (Greg Grimes) writes: >>In an article, chandoni@husc9.harvard.edu (A Potential Security Problem) writes: >>> >>>Question 2: >>> Is there a way to boot from drive B: (on my system, a >>>3.5" drive) without switching the hardware? ... > >>PC/Computing magazine threw this question out to readers last July >>and there were at least two answers: (1) pull the skin off and swap >>floppy cables (making A: B: and vice versa), or (2) there is actually >>some software that does this you can buy. Didn't say how. My guess >>is that it scrambles BIOS' ideas as to which floppy is which during >>the boot process. > >I have a short program called BOOTB and all it (I think) does is put some >information on the boot sector of a floppy that you stick in your normal boot >drive. The code tells the computer to get the rest of its boot code from >drive B. Supposedly, its as simple as that, although I've never used it (and >I'm not even sure I've still got it.) I found it on a local BBS where I used >to live, so I'm pretty sure its not commercial. >If I remember correctly, the documentation for it said it would work for most >software that followed normal DOS stuff (and I really have no idea what that >means.) =) > >James Gurganus (gurganus@ecn.purdue.edu) I wrote something similar (also called it BOOTB :-), that read the boot sector from drive B: and executed it. Didn't work because normal DOS boot sector programs are hard-coded to read from A: (ROM BIOS read gets a 0 in DL). There's a spot in the boot sector (it's different for different versions of DOS) that contains the code that gets splatted in DL. This is changed to 0x80 for hard disks. I changed this byte to a 1 to make the boot program read from B:. Still didn't work. I gave up at that point. If you ever try BOOTB (the one you got from the BBS :-) and it works, I'd really like to know how. If you send me a copy I'll disassemble it and report. Try it first, though, I don't think it'll work because the problem's in the boot code on the B: drive, not the BOOTB code in the A: drive :-) -- Greg Grimes | "Sit down, please. There are a thousand questions I'd AIX Host Development | like to ask you." -- Prof. Jacob Barnhardt to Klaatu sasgig@unx.sas.com | ("The Day the Earth Stood Still")