First introduced on the Sony Discman some years ago, Electronic Shock Protection (ESP) works by reading the CD faster than the standard 1X (150kB/sec) required for normal CD playback and storing the data in a memory buffer. This was done so that if the optical pickup is jolted out of alignment by an external shock, the CD player would read from the memory buffer until the pickup came back on track and resumed reading. While this would in most cases (except for the very early incarnations) provide people with (mostly) skip-free music, the increased read rate and the power required to maintain and write to the memory buffer meant that the activation of ESP would mean a fairly noticeable drop in battery life. While Sony was the first to introduce this new technology, others soon followed and now most CD players have this feature under a similar name.
Early versions of ESP provided a measly 3 seconds, then 6, then 10. ESP2 was introduced some years later, which used a 16MB buffer in order to provide a significantly higher amount of protection. ESP has now been replaced by Sony's new G-Protection system.