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Re: Image file too large for low memory


On Tue, Feb 18, 2003 at 07:51:03AM +0100, Thorsten Sauter wrote:

> Hello,
> On Tue, Feb 18, 2003 at 01:04:55AM -0500, Owen B. Mehegan wrote:
> > Node: 00B0D0A42B88
> > DHCP...
> > TFTP............................
> > File transfer error: Image file too large for low memory.
> are you sure, that the error message means the memory for you laptop.
> How many ram is available in this beast? :)
> While playing with tftp and network boot, I'll got this error message on
> many machines (i386, 3com or intel nic). The machines have 32MB and up
> to 512 MB ram, so a small 1.44MB floppy should be small enough to fit
> into the memory.

Ah. Welcome to the lovely 16-bit boot process of Intel machines.


Intel boxes boot up in real mode, in which 8086-style addressing is
enabled. In this mode, you don't have 32-bit memory offsets, but rather
16-bit segment addresses that are shifted 4 bits to the left before
adding a 16-bit offset address, forming a 20-bit address.

In short, until something switches the CPU to protected mode that uses
segment registers in a wildly different fashion, software can only
address the first megabyte of memory. The PC normally has up to 640 kB
of RAM in that first megabyte; the rest contains part of your
framebuffer and some ROM. So that's all you can access during the boot


So if the NICs boot ROM contains only real mode code, 1.44 MB will
indeed /not/ fit into memory. Try a bare bones kernel; 512 Kb should
definitely work.



E-Advies / Emile van Bergen   |   emile@e-advies.info
tel. +31 (0)70 3906153        |   http://www.e-advies.info

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