SBD II: adds a tri-mode seeker and wing kit (like the MBDA Diamond Back kit for current JDAMs) giving it extended range compared to traditional free fall bombs.
FLM: Composite case SBD with focused blast explosives. Its designed to reduce shrapnel and focus the blast down instead of out.
I'm sorry, bjr1028, but your facts aren't quite correct. The SDB (not SBD) is NOT a mini-JDAM at all. It is a completely new "bomb", really an unpowered missile, whose wings, GPS receiver, explosives, casing etc. are all part of a single, unitary package. Nothing bolted on as with the JDAM. It was never originally an unguided bomb with a guidance package strapped on. The SDBII adds a tri-mode seeker only. The "wing kit" (not really a kit as it is an integral part of the "bomb") is part of the original, plain-vanilla SDB. You are basically correct about the FLM.
Well, I'm not sure any of you got that 100% correct. The SDB I is either a GBU-39A/B or a GBU-39/B. The GBU-39A/B is a Focused Lethality Munition (FLM) meaning instead of a steel warhead as in the GBU-39/B it has a composite case filled with a Multi-Phase Blast Explosice (MBX) and is used for collateral sensative targets vs the GBU-39/B which can be used against things where your not worried about collateral damage.
The SDB II GBU-40/42 version is supposed to have the ability to loiter and should be able to hit mobile or movable targets in all weather. Its supposed to be equiped with a Lockheed Martin's tri-mode seeker which features a radio-frequency mode that can function out to 10 km, an imaging infra-red mode that sees out to about 5km and then a laser-guidance mode, a Harris data link, and two-way communication . The weapon receives in-flight target updates using a tactical radio communications system, which are then processed by the seeker. Using the updates, the seeker should be able to search, detect, track, classify and destroy a target.