can't assign enough RAM to the VM

QEMU version: 1.6.90.0 from 2013 11 16
Host OS: Windows XP SP3 x86
Host machine: 3.2 GHz AMD Athlon 64 dual core processor, 4 GB DDR II (3.2 seen by the OS) memory
Guest OS: Grub4Dos boot manager menu
Problem: you can't assign more than 880 MB memory to the VM, although with 0.15.1.0 version you can assign up to 1179 MB.