Welcome to MUB,
"SD" partitions are for "Special Devices" such as External Harddrives and CF cards. Your "normal" partitions are usually on "HDA" or the main harddrive. Tho I prefer Arctic's method personnally, you can also enter the following via a terminal window to list your harddrive's partitions and it will give you some usefull info:
df
sda1 and sda6 should be on the same drive... where sdb will be another drive.
You have any USB drives, card readers, zip drives, etc. installed on this system?