I have an 80GB disk in my DNS-323 FW v1.04 HW vB1, the partitions look like this:
Disk /dev/sda: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 66 530113+ 82 Linux swap
/dev/sda2 131 9729 77103967+ 83 Linux
/dev/sda4 67 130 514080 83 Linux
It looks like:
the first 66 cylinders are allocated to a primary partition #1, type 82 Linux swap
the next 64 cylinders are alloaded to an extended parition #4, type 83 Linux
and the rest of the disk is allocated to a primary parition #2, type 83 Linux