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