TAR FAILURE ON LARGE FILE (NT)

[colin.mcgeoch@gro-scotland.gsi.gov.uk]

Hi,
When I run 

?tar -cvf - sourcefilename>targetfilename? (in a DOS window) on a
file of size 4,415,176,704 bytes, the resulting TAR file only has size
120,217,600 bytes , although no error messages are given.  In contrast, the same
command works successfully on a smaller file (eg 120,217,600 bytes).

The only archives reference I have found on tar/large files seems to relate to a
different problem on much smaller files(25MB). I have only recently started with
cygnwin, so apologies if I have nissed something obvious.

Is there a file size limit on using tar ?
Could tar be finding a byte which fools it into thinking it has reached the end
of the file when it hasn?t ?

Thanks
Colin