[syslinux] 2GB USBkey and mkdiskimage

Josh Lehan jlehan at scyld.com
Mon May 8 11:49:21 PDT 2006

Ole Jacob Taraldset wrote:
> On Friday 05 May 2006 16:12, H. Peter Anvin wrote:
>> Ole Jacob Taraldset wrote:
>>> Is there any way around this or is it just not possible to make this
>>> USBkey look like a Zip drive?
>> Sort-of-kind-of.  If you're sensitive to geometry, you care about C/H/S
>> addresses, which does require that C <= 1023.  What you can do is you
>> could create a drive with two partitions and boot from the firs one.
> Thanks for your answer. How exactly would you do that?

I wonder if you could do what the HP formatter tool does for USB 
thumbdrives: make a partition with truthful values in the LBA sector 
start and size fields, but lie in the CHS fields.

The HP formatter does this, and it seems to work.  It chooses the 
biggest possible full cylinder boundary, and sets CHS values to these, 
even though it is less than the LBA sector size.  It then patches the 
standard Windows XP MBR to always use LBA INT 13 calls, and not use the 
old CHS calls at all.

I wonder what results you would get, by manually editing your partition 
table to have ending CHS of the max for USB-ZIP, 1023/64/32?

(My USB thumbdrive only is 1GB, so I can't try this.)

The LBA sector count would not be patched, and remain truthful, set to 
whatever is the true size of your USB thumbdrive (around 2GB or so).  To 
tell Windows to use only LBA, choose filesystems with LBA partition 
types (0x0C or 0x0E), not the old CHS partition types!  Then, CHS should 
not matter, as it will only be used by the BIOS to recognize the drive 
in the first place.

Patching mkdiskimage to cap the cylinder count at 1023 might work.  It's 
worth an experiment....


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