strange code in startup function

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Hi all,

Can anybody please explain what the following piece of code does?

http://lxr.linux.no/source/arch/i386/boot/compressed/head.S

arch/i386/compressed/head.S (startup_32)
---------------
41         xorl %eax,%eax
42 1:      incl %eax               # check that A20 really IS enabled
43         movl %eax,0x000000      # loop forever if it isn't
44         cmpl %eax,0x100000
45         je 1b
-------------

the value in eax is first made 0 and then incremented by 1.
What will be the impact of line 43 and 44 in above lines of code?

Thanks in advance.
Amrut.

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