[syslinux] ISOs + memdisk take long time

[Gene Cumm]

As far as the transfer speed, I can speak from some similar experience
with some educated guesses for reasons.

On Fri, Mar 12, 2010 at 9:08 AM, MALTE SIMON <malte_simon at hotmail.com> wrote:
> My problem it take up to 30sec until the ISO is booted

I'm assuming this means it takes a boot loader like SYSLINUX and your
BIOS 30s to transfer data.

On Fri, Mar 12, 2010 at 1:12 PM, MALTE SIMON <malte_simon at hotmail.com> wrote:
> My Iso is 72mb it take 15-20 secend to copy it to my hdd

I'd assume you're using real operating system here.  For reference,
copying to a null device (a bit dump; ie /dev/null or NUL:) should
give you the fastest speed possible (assuming your computer is
otherwise idle).

I'd also assume this is the same machine for both tests with the USB
drive plugged into the same port and the same exact file with no
difference in the USB drive.

I've noticed similar behavior across different machines and BIOS
revisions.  I saw some early machines (vintage 2002) with hardware
High Speed support (480 Mbps; sometimes referred to as USB 2.0 as HS
was introduced in 2.0) functioned like Full Speed (12 Mbps; sometimes
USB 1.1) using SYSLINUX but would function faster in a real operating
system.  I've also seen more recent laptops with a BIOS option to
throttle the USB to 12 Mbps (claimed in an effort to conserve battery;
not personally confirmed).  I've seen machines from around 2006-2008
that would move data faster than 12Mbps but not at the speed seen in a
real operating system, like you've seen.  Only some of the most recent
machines I've seen perform similarly in SYSLINUX and a real operating
system.

My guess here is the distinction lies in the efficiency of the BIOS to
perform transfers on the USB drive, which is emulated as a Legacy BIOS
disk (similar to an IDE disk) in order to be accessible from BIOS
calls.

-- 
-Gene