The pattern buffer is a key component of the transporter system. The buffer is used to temporarily store the matter stream, following dematerialisation, but prior to sending the stream to its target. This is done because of the relative motion of transporter and target. By temporarily storing the matter stream the Doppler compensators have the time to adjust the targeting scanners.
A matter stream cannot be stored indefinitely in the buffer, after 420 seconds the stored pattern will degrade and the object will lost. The only known record of a person surviving in a buffer longer than the expected figure was Captain Montgomery Scott onboard the USS Jenolan. Following the Jenolan's crash-landing on a Dyson sphere, Scott, with the help of Matt Franklin, was able to store his pattern in the buffer for 75 years. This was achieved by disabling the rematerialisation subroutine, connecting the phase inducers to the emitter array, bypassing the override, and locking the buffer into a continuous diagnostic cycle. Although Captain Scott's pattern suffered less than 0.003% degradation, and was successfully recovered by Geordi La Forge of the USS Enterprise-D, Franklin was irretreivable, as one of the inducers had failed, causing a 53% degradation in his pattern. (TNG: "Relics")
On Galaxy-class starships the pattern buffer is located immediately beneath the transporter pad.
Starships can also transfer patterns from one pattern buffer to another by 'locking on' to the target buffer and energizing. (VOY: "Future's End, Part II")
To eliminate the medical condition called: Transporter psychosis, federation transporters are equipped with multi-plex pattern buffers
Cardassian transporter systems are equipped with active feed pattern buffers.