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authorH. Peter Anvin <hpa@zytor.com>2008-03-01 15:56:29 -0800
committerH. Peter Anvin <hpa@zytor.com>2008-03-01 15:56:29 -0800
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+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.