A positive adjustment voltage regulator. Manufactured in vast volumes by National Semiconductors, this linear circuit is packaged in a TO220 package. It costs about $1,5 unless you buy outrageous quantities. This specific semiconductor received some extra attention after the release of the Abit BP6 motherboard, which could modified to run dual Pentium-III processors in SMP mode, but needed this circuit to do so and still stay stable. Unfortunately, the most common LM338 variant is packaged in a TO3 capsule, unsuitable for soldering onto your motherboard.