doc/usbkey.txt - platform/external/syslinux - Git at Google

 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 0 64 32

 (The 0 means automatically determine the size of the device, and -4
 means mimic a zipdisk by using partition 4.)

 Then you should be able to run

 	syslinux /dev/sda4

 ... and mount /dev/sda4 and put your files on it as needed.
	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 0 64 32

	(The 0 means automatically determine the size of the device, and -4
	means mimic a zipdisk by using partition 4.)

	Then you should be able to run

	syslinux /dev/sda4

	... and mount /dev/sda4 and put your files on it as needed.