Booting from PCMCIA disks

CompactFlash memory disks have become really cheap and a CompactFlash->PCMCIA adaptor is about $10. This makes it attractive to use a CompactFlash card as the only disk drive in a laptop to get.

Low power consumption.
Low noise.
A way to boot the laptop. You might not have a harddisk or the disk caddy for your laptop.

Some laptops, e.g. the IBM Thinkpad 365 used for The picture frame project can boot from a PCMCIA drive. This has the added bonus that then the linux kernel boots, the PCMCIA drive is already initialized and any partition on the drive can be mounted as the root-partition.

Other laptops, e.g. my Thinkpad 770 cannon boot from PCMCIA. You could then boot the laptop from a floppy-drive and mount the PCMCIA-partition as /. However the PCMCIA system have not been initialized yet, so the kernel cannot mount its root.

The pcmcia-cs project has a pcinitrd script that creates an initrd ram disk image for booting with the root file-system on a PCMCIA device. But is it too big for a floppy disk. It is about 2.5 MByte not including the linux kernel.

Instead I modified the cardmgr.c program from the pcmcia-package to remove unnecessary code, mount /proc, mount a tmpfs drive, set up the card in the first PCMCIA-slot, do a pivot_root() to the new root fs. This is the only program on the initrd. There is not shell. The result is an 212KByte initrd leaving space for even a fat 2.6 kernel.

Limitations

The initrd can only mount the following file-systems: reiserfs, minix, ext2, xfs, cramfs
The kernel on the floppy image can only mount mount: reiserfs, minix, and cramfs
The initrd only inserts the pcmcia-card in the first slot.
There are no modules on the initramdisk. So if you make your own kernel, "pcmcia" and "ide-cs" has to be compiled into the kernel, not as modules.

How to make the CFlash root file system

Well, that depends on what distribution you want. You might try a small distribution LinuxPuppy or "Damn Small Linux".

I prefer Debian. I run debootstrap on a laptop with a harddisk. chroot to the new root directory and install what I need with apt-get. I have installed xfce4, firefox, thunderbird.

download

The floppy image
only the init ramdisk
cardmgr source. Compile it statically with uClibc.
config for the 2.6.10 kernel on the floppy image. If you want to add modules to the PCMCIA disk without replacing the kernel on the floppy.

This work is licensed under a Creative Commons Attribution 2.5 License.

Niels Elgaard Larsen

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