MIL Standards and Specifications
The Armed Forces have many numerical designations for computers or other equipment, to guide the military buyer's choice of appropriate technology for their application. For instance, MIL-STD-901D would indicate that the computer passed shock and vibration requirements of specific tests for Navy installation. Some of these tests are specific to application usage, such as barge explosion testing, which simulates a torpedo hit and subsequent high peak shock to a ship on which the computer is installed.
MIL-STD-901D is divided into Grade A for "Items which are essential to the safety and continued combat capability of the ship" and Grade B for "items whose operation is not essential to the safety and combat capability of the ship but which could become a hazard to personnel, to Grade A items, of the ship as a whole as a result of exposure to shock".
In this way, a computer may have a rating of MIL-STD-901D Grade A, which would tell a buyer which shock tests the computer survived, what level of shock resistance the unit has, and that this piece of equipment will continue to normally operate in the event of a specific shock level.
Other MIL Standards and MIL Specs (Specifications) include testing for resistance to EMI/RFI bursts, environmental contaminants such as dust and gas, or temperature extremes. More on MIL Standards and Specifications at Defense Standard.
The "gold standard" of testing for compliance with 901D is the Barge Test. A Barge Test is performed four times, each time placing 60 lbs HBX-1 explosive 24 feet under water, starting at 40 feet away, then at 30, 25 and finally 20 feet. In addition, the tests are performed in a fore-and-aft orientation to simulate an explosion at the bow or stern of the ship and athwartship to simulate an explosion by the side of the ship. A video of a barge test can be viewed.
Typically a military computer is much more robust than an industrial computer enclosure. There will be more structure inside to support the components, the plug-in cards will be individually supported and secured to assure they do not pop out of their sockets, the processor and heat sink will be secured, memory will be glued into their sockets, and so forth. This is to assure nothing moves during the shock events.
Read more about this topic: Military Computers
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