The output of the show idb command looks similar to this:
Router#show idb
Maximum number of IDBs 4096
42 SW IDBs allocated (2440 bytes each)
40 HW IDBs allocated (5760 bytes each)
HWIDB#1 1 SRP0/0 (HW IFINDEX, SRP)
HWIDB#2 2 POS1/0 (HW IFINDEX, SONET, Serial)
HWIDB#3 7 FastEthernet3/0 (HW IFINDEX, Ether)
HWIDB#4 8 FastEthernet3/1 (HW IFINDEX, Ether)
HWIDB#5 9 FastEthernet3/2 (HW IFINDEX, Ether)
HWIDB#6 10 FastEthernet3/3 (HW IFINDEX, Ether)
For more information : http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_tech_note09186a0080094322.shtml