having 1.5GB RAM I cannot allocate more than 512MB RAM in 4.10

[dkouroun at cc.uoi.gr]

Dear FreeBSD list,
I have an AMD Athlon-XP with 1.5GB RAM.
Unfortunately my FreeBSD 4.10 throws a memory allocation 
error when in a simple C++ program I try to allocate 
with new 512MB of RAM or more. Until 511MB it goes fine!

Is there any kernel specific feature I should tweak? 
What is the problem here? I didn't have such problems
with 5.3 Release although it is generally more unstable!

Here is the simple C++ program I used:
--------------------------------------

#include <iostream>
using namespace std;

int main(int argc, char* argv[])
{
   if (argc != 2)
   {
      cout << "usage: " << argv[0] << " mem(memory to allocate in bytes)\n";
      cout << "examp: " << argv[0] << " 1024\n";
      exit(1);
   }

   long int bytes = strtol(argv[1], NULL, 0);
   char* buffer = new char[bytes];
   cout << "memory allooated succesfully = " << bytes/1024.0/1024.0 << "MB \n";
   delete[] buffer;
   cout << "allocated memory is now free\n";
   return 0;
}

#g++ memalloc -o run
#./run 536870912

which when I tried to run gave a:
---------------------------------
terminate called after throwing an instance of 'std::bad_alloc'
  what():  St9bad_alloc
Abort (core dumped)

Here is the output of my top command:
------------------------------------
last pid:   432;  load averages:  0.00,  0.00,  0.00  up 0+00:35:23    13:37:10
38 processes:  1 running, 37 sleeping

Mem: 63M Active, 39M Inact, 55M Wired, 24K Cache, 50M Buf, 1343M Free
Swap: 3056M Total, 3056M Free


  PID USERNAME PRI NICE  SIZE    RES STATE    TIME   WCPU    CPU COMMAND
  183 root       2   0 84824K 19864K select   0:05  0.00%  0.00% XFree86
  190 root       2   0  8916K  7720K poll     0:02  0.00%  0.00% gconfd-2
  360 root       2   0 10620K  9720K select   0:02  0.00%  0.00% emacs
  242 root       2   0 12464K  9124K poll     0:02  0.00%  0.00% metacity
  248 root       2   0 21148K 15472K poll     0:01  0.00%  0.00% nautilus
  246 root       2   0 17032K 13108K poll     0:01  0.00%  0.00% gnome-panel
  264 root       2   0 16104K 12124K poll     0:01  0.00%  0.00% wnck-applet
  266 root       2   0 14148K  9560K poll     0:01  0.00%  0.00% mixer_applet2
  188 root       2   0 16124K 10760K poll     0:01  0.00%  0.00% gnome-session
  197 root       2   0 16076K 10288K poll     0:01  0.00%  0.00% gnome-settings
  268 root       2   0 14924K 11012K poll     0:00  0.00%  0.00% clock-applet
  108 root       2   0   920K   528K select   0:00  0.00%  0.00% moused
  270 root       2   0  4492K  3552K select   0:00  0.00%  0.00% xterm
  432 root      31   0  1912K  1084K RUN      0:00  0.00%  0.00% top
  195 root       2   0  5188K  3588K poll     0:00  0.00%  0.00% bonobo-activat
  250 root       2   0  6552K  3928K poll     0:00  0.00%  0.00% gnome-vfs-daem
  271 root      18   0  1424K  1172K pause    0:00  0.00%  0.00% csh
  240 root       2   0  7688K  4656K poll     0:00  0.00%  0.00% gnome-smproxy