Shared memory segment IDS 9.4

Hi, I defined 1200000 BUFFERS in $ONCONFIG file for IDS 9.4/AIX 5.3. I used a formula from Performance Guide and counted that the buffers should take in resdident portion of shared memory about 1200000 * 4 kB + 1200000 * 254 ~ 5 GB. I started IDS and found ( onstat -g seg ) that resident portion of shared memory was about 4,2 GB ( more less than I expected ) and virtual segment was very large. I found in machine notes that "The maximum size of any shared memory segment is 4294705152 bytes", so I thought that AIX could not make more then 4,2 GB segment for the buffers. How did IDS create 1200000 buffers in this situation? Are the over resident segment buffers moved to virtual segments, or IDS creates only so many buffer that can be held in resident portion? Thanks, Wojtek