We have four KVR533D2SS8F4/512 memory sitting in the FB-DIMM slots on the Tyan Tempest i5000PX motherboard. We want to use 512MB shared memory for our data acquisition. As this motherboard has four memory channels, we thought to use 128MB from each chip. Now when we initilize shared memory with "shmaddr" argument is zero in "shmat" system call, operating system pick address "0x672e7000" and in this case full SHM are sitting in one RAM stick. I can't able to attach the share memory at any other user given address (except 0x672e7000). How can there be only one valid address which operating system has picked up? For all other address shmat returns 0xffffffff as the address of the attached shared memory segments.