This idea keeps popping into my head when answering the almost daily "how do I dual-boot?" threads. Time to write it down..

Why not install a switch that changes the drive order as seen by the BIOS? Using this, the process to switch OSes would be virtually idiot-proof:
shutdown (restart)
At the beep (when POST starts), flip the switch.

I think I know enough about IDE to do this--not sure about SATA. But--in principle, you could have a multigang switch that toggles the entire interface.
The other method would maybe be to just interface the switch to the drive jumpers (Do SATA drives still HAVE jumpers?)

Wouldn't this then cause problems with the lilo or grub config? Or will the config files allow two entries with the same root device? (i.e. the first install would have /dev/hda1 and so would each additional install)

This would completely bypass the grub selection menu--each hard drive has its own boot-loader pointing to only one kernel on the same drive. Functionally, it would be the same as switching boot order in the bios---only fewer keystrokes (and no need to remember which key to press to get into BIOS config menu)

Ah, missed the single os per hard drive thing (I dual boot with one drive and use the other for backup purposes)... Sounds like it would work fine on a desktop, probably not so well on a laptop.

So far, I have discovered:
SATA has no jumpers on the drives (one device per port), therefore one needs a switch.
At least one company (Indus) makes these, but not cheap ($150 +)

Hacking the mobo could--I suppose--be an option for the brave.....

It might be a fun experiment, but setting up multiboot is so easy that it doesn't seem like you need a hardware solution. The problem for the new guys is wading through the huge number of posts, and even some books have confusing/incorrect explanations.

I agree---it is easy--once you know how..

I advocate having "stickies" in--as a minimum--the newbie and general sub-forums. These would contain the very best concise instructions that we can collectively generate.

The appeal of the hardware solution includes the ability to change drives and re-install OSes without ever touching a grub config file again. Or to reinstall windows without any other steps needed to restore access to Linux......etc.

Actually, I would love to invent a dual-boot motherboard/bios combo. Hit a switch--or a control key sequence--and the machine morphs into a new persona. A good project for the next life....??

I would laugh at such a childish concept.

Grub has a "map" command to alter the disk order on-the-fly. To make the second disk (hd1) to boot as the first disk (hd0) (Grub counts from 0!!!) the commands are
Lilo also has map-drive comand to do the same thing except Lilo calls the 1st, 2nd , 3rd and 4th drives by 0x80, 0x81, 0x82 and 0x83 respectively. Thus to do the above in Lilo the commands are
The above are documented in Grub manual and Lilo User Guide. They work perfectly.

If one has to re-invent a wheel, try to invent a round one. Square wheel doesn't look or work that well.

I boot over 100 systems in my box and I just don't think buying 100 switches is the right way forward when both Linux boot loaders have the above software switches ready made for us.

Saikee;
I have enormous respect and admiration for your multi-booting prowess and I refer people to your writings with great regularity.

I can and will accept input which articulates the ways in which my idea is not among my best, but "childish" is taking it a step too far.

The FACT is that setting up dual-booting can be a hassle. Further, (my assertion) there are people who might benefit from something simpler.

pixellany,

I actually agree with you and I know there are a few commercial product switches available to just fit your demand. There are definitely horses for courses.

The "childish" is more of a "comparison" for avoiding the simple statements in either Grub or Lilo in preference to a more difficult way of installing a electrical switch.

I am making fun out of the situation by pointing out the "software switches" are already available in case people are unaware of them.

You can take my word that once you use the software switches once you will never want to know the physical type.

I often leave a Grub floppy in the drive so that I could boot the PC up without using the MBR. I also could have any combination of my 4 hard disks inserted (they are in caddies/mobile racks). Using the software switches at a Grub prompt is all I do to select which disk and which system to boot to. Thus software switches are many times faster and more flexible than toggling a set of electrical switches.

I think many Linux users are not aware of the ease and power of booting a Linux or a Windows up manually using the same instructions as stated in /boot/grub/menu.lst and access to a rich set of Grub commands available at Grub prompt. There is no PC system that I know that cannot be booted by a Grub floppy. The map statement (software switch) is part of the rich set of commands available to any user whenever he is in a Grub prompt.

If you are in a Grub prompt, available from booting up a floppy with only Grub's stage1 and stage2 files, the system rarely hangs. Therefore you can try to boot the system up "repeatedly" until it works. It is "best" way to learn how to boot using this trail and error approach. Once the manual commands have been found they are the very statements required in Grub's menu.lst.

Thus the universal cure to any booting problem is to have a bootable Grub floppy (or CD for laptop users) available.

An **I** agree with **you**---isn't all this harmony wonderful?....

For every user who appreciates the power of grub, there is at least one who is too lazy---ie just wants to "push a button". One of my issues with the MS world is that it too often caters to the lazy camp.

My curiousity on the hardware solution is simply whether it is possible.

With older IDE hard disks you could rig a switch on the master/slave jumper. Newer drives are cable select, so which connector on cable you use matters. I imagine you'd also run into interference problems with higher speed drives trying to switch all 80 conductors, since half are really only used as shielding. Anyway, sounds like a whole lot more trouble to me. I'm lazy and just use GRUB. Linux install set all that hard dual boot stuff up for me automagically; I didn't have to do anything. hehe

Pixellany, if you really want to do us favor, why don't you take up some C for few years
and devise some clever way of building qemu or something like that into the kernel. Use as little emulation as possible, give the host OS direct hardware access(basically I wanna be able to play 3d games with NO performance lost at all), and THEN you make you switch(a digital one would be prefered so I have any physco number of OSes installed on my computer) and program the switch to tab between operating systems. There, no reboot, no grub configuration. For additional lazyiness, I would also like (working!) voice recognition built-in. But sometimes my voice gets tired too, so if you could invent computer thought recognition as well I would greatly appreciate that too.

But now that I think about it, this whole multiple operating system thing is also too much effort. Since we got you learning C and all, I suppose we could also have you build an operating system, one that really really works. Zero effort configuration, infinitely scaleable, never crashes,responds to thoughts, requires no physical effort, self-upgrading, boots instantly,is free, can transform imagination into reality basically.

I believe the hardware switch if applied will only need to switch the 4-pin 12/5 VDC supplied. Not so sure about the interference in the 80-wire ribbon cable but I would have expected the design should be able to withstand it.

I had in the past just pull the power supply off the hard disk that I didn't want to operate (while the PC is off) but could not remember any problem encountered. In "cable select" position the remaining disk should take over as the master as there is no other device. Preferrably it is the hard disk in the middle of the cable to be stopped.

For Sata the remaining unit seems to take over the sda1 automatically.

May be I have gone about the argument the wrong way. I have stated at the beginning that I have put all my hard disks in caddies so that I could put any of them as master or slave (in any hda, hdb, hdc & hdd) position. I do this to my two Sata drive too. So effectively I am using the hardware switching all the time myself.

I haved also screwed a couple of the mobile rigs to external hard disk enclosures and so any of my hard disks can be used either as internal drives (run at ATA133) or external hard disks limited by the USB2 ports.

In the above application I achieve all the benefits of the hardware switching without using a single hardware switch.

In UK a mobile rig set cost about 5GBP and a good quality dual pole electrical switch, say rated at 10A, can cost over 3GBP. May be using the mobile rack is a better option. There are 3.5" to 2.5" hard disk adaptors availble so laptop hard disks (2.5") can be used just same as the standard 3.5" hard drive in mobile racks.

The downside of the mobile racks is a cheap fan is usually supplied to assist cooling. This cheap fan wears out very quickly (after about 6 months) and produces irrating noises. I have removed all of them just to have a quiet surrounding. The cheap fan may be needed if the disk is run permanently as a server.

Thus I do agree switching is desirable but possibly not using electrical switches if there are easier and more flexible alternatives available.