Documentation about USB keys

diff --git a/NEWS b/NEWS
index 48b4a68..ce3533b 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -36,7 +36,11 @@ Changes in 3.00:
          to write an MBR and -a to mark the partition SYSLINUX is
          being installed on active.
        * MEMDISK: Give a way to query the boot loader type while
-         running MEMDISK; see memdisk/memdisk.doc and sample/mdiskchk.c.
+         running MEMDISK; see memdisk/memdisk.doc and
+         sample/mdiskchk.c.
+       * mkdiskimage: substantially improved mkdiskimage which, among
+         other things, can now be used to initialize USB keys as
+         zipdrives; see README.usbkey for more information.
 
 Changes in 2.13:
        * MEMDISK: Fix command-line parsing "brown paper bag" class

diff --git a/README.usbkey b/README.usbkey
new file mode 100644 (file)
index 0000000..4154cce
--- /dev/null
+++ b/README.usbkey
@@ -0,0 +1,46 @@
+$Id$
+
+The proper mode to boot a USB key drive in is "USB-HDD".  That is the
+ONLY mode in which the C/H/S geometry encoded on the disk itself
+doesn't have to match what the BIOS thinks it is.  Since geometry on
+USB drives is completely arbitrary, and can vary from BIOS to BIOS,
+this is the only mode which will work in general.
+
+Some BIOSes have been reported (in particular, certain versions of the
+Award BIOS) that cannot boot USB keys in "USB-HDD" mode.  This is a
+very serious BIOS bug, but it is unfortunately rather typical of the
+kind of quality we're seeing out of major BIOS vendors these days.  On
+these BIOSes, you're generally stuck booting them in USB-ZIP mode.
+
+THIS MEANS THE FILESYSTEM IMAGE ON THE DISK HAS TO HAVE A CORRECT
+ZIPDRIVE-COMPATIBLE GEOMETRY.
+
+A standard zipdrive (both the 100 MB and the 250 MB varieties) have a
+"geometry" of 64 heads, 32 sectors, and are partitioned devices with a
+single partition 4 (unlike most other media of this type which uses
+partition 1.)  The 100 MB variety has 96 cylinders, and the 250 MB
+variety has 239 cylinders; but any number of cylinders will do as
+appropriate for the size device you have.  For example, if your device
+reports when inserted into a Linux system:
+
+usb-storage: device found at 4
+  Vendor: 32MB      Model: HardDrive         Rev: 1.88
+  Type:   Direct-Access                      ANSI SCSI revision: 02
+SCSI device sda: 64000 512-byte hdwr sectors (33 MB)
+
+... you would have 64000/(64*32) = 31.25 cylinders; round down to 31.
+
+The script "mkdiskimage" which is supplied with the syslinux
+distribution can be used to initialize USB keys in a Zip-like fashion.
+To do that, calculate the correct number of cylinders (31 in the
+example above), and, if your USB key is /dev/sda (CHECK THE KERNEL
+MESSAGES CAREFULLY - IF YOU ENTER THE WRONG DISK DRIVE IT CANNOT BE
+RECOVERED), run:
+
+       mkdiskimage -4 /dev/sda 31 64 32
+
+Then you should be able to run
+
+       syslinux /dev/sda4
+
+... and mount /dev/sda4 and put your files on it as needed.