Missing memory (RAM)

I’m running x86 on a PC104 board from SECO. Type M570 (600 MHz), see also www.seco.it. On board there’s 256 MB of DRAM.

But the problem is there’s only 64 MB accessible by QNX. Where’s the other 192 MB? The command pidin in says: FreeMem: 16MB/64MB

Does somebody recognize this problem?
How can I get access to the full memory of 256 MB?