Can You Boot Windows (and Other OSes) Using CD-RWs?

CTho9305 asks: "I know you can make bootable CD-R/RWs that work fine to get you running DOS (well, Microsoft will call it Windows without the GUI, but I'll call it DOS). And I know you can boot linux, and even run X. However, that only works because these things can run fine from read-only media. Since a CD-RW could theoretically be mounted read-write under linux, I bet its possible (if it hasn't alread been done) to write a kernel module to boot from a CD-RW with it mounted read/write. What I'm really interested in is booting Windows (9x), which requires read-write media. What would be required? Would a DOS driver suffice? Does such a piece of code exist somewhere?" Such an ability would make it easier for novice users to try other alternative operating systems. Is it likely that BIOS makers will support this ability in the future? What can we do to make this happen?

Comments

Re:Windows _can_ boot from CD

[g_attrill]

You can view it here without having to pay.

Gareth

Connectix

[dodecahedron]

Such an ability would make it easier for novice users to try other alternative operating systems.

If the objective is to let users try alternative operating systems, consider using the new Connectix Virtual PC for Windows. It allows you to install another OS (DOS, Linux, BeOS, etc.) under Windows, where you can try it out just as though it were the native OS. Connectix is offering a free trial download that will work thru July 1.

Booting Windows from RAM

[levendis]

I'll describe a little experiment I tried a while back, just to see if I could. You might find it useful.

First, there are numerous utilities out there to create RAM disks... device drivers you can put in CONFIG.SYS to give you a drive letter which exists in RAM. Now, the only one I could find was limited to 32 megs. Not enough space? Bah! I installed Windows 95 (the original version) on the hard drive, and was able to delete unnecessary files (help files, etc) to trim the windows directory down to about 25 megs. Also had to disable virtual memory, but I had enough left over RAM that it didn't really matter.

Now, there are a few tricks you need to know to get Windows to boot out of a RAM disk. First, you need to 'subst' command, which lets you raassign drive letters to other directories. For example:

subst x: c:\xdrive

Will let you access c:\xdrive as drive X:. The cool thing is you can reasign existing drive letters:

subst a: c:\floppy

So now A: is just a "symlink" to c:\floppy

Also, you need to know how to do a soft reboot of Windows. If you hold down "shift" when hitting the OK button in the restart dialog, windows will restart but not actualy reboot the computer - so the contents of your RAM disk will stay around. This is basically what happens when you have windows run in "MSDOS mode"... it does a soft restart to a DOS prompt, then when you type exit it restarts Windows without a reboot. So, you can just make a shortcut to an empty batch file, set it run in MSDOS mode, and when you run the shortcut, Windows will do a soft restart.

So, all you need to is write a batch file to run at startup which does the following:
1) copy the Windows directory into you RAM disk R:
2) delete this batch file from the RAM disk
3) subst c: r:\
4) do a soft restart

Now, when you boot your minimal Windows from the hard drive, it will copy itself to RAM, switch the C: drive to the RAM drive, and soft restart itself from the RAM disk. It takes about 2-3 seconds for Windows to do a complete soft restart.

Yoy might be able to do the same thing from a CDROM.

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Here you go

[PatJensen]

Here is the Windows bootable CD HOWTO article in English. The lowdown:

Regular backups often only offer a false feeling of security: After a system crash Windows frequently doesn't even start up anymore, and this puts the restore program out of reach, too. Therefore, a bootable and virus-proof Windows installation on CD ROM should really be found in every well-stocked emergency kit.

'To start Windows 95 or 98 in GUI mode, it must be installed on a writeable medium. You cannot start Windows from CD.' Similar statements have been published in various PC magazines, and c't has said it, too. The time has come to revise this statement.

The reason for this assumption lies in the fact that Windows spits out masses of error messages when unable to access the registry during startup. However, this is essentially only cosmetic: If you can live with it, Windows 9x can indeed be started from a CD ROM. This article will deal with how to eliminate the error messages and optimize CD ROM booting.

Have fun!

-Pat