Speed and Thrash
Speed metal is a loosely defined sub-genre of heavy metal that spawned in the mid-late 1970s and was the direct musical progenitor of thrash metal. When Speed metal first emerged as a genre, it innovatively increased the tempo of the music template set forth by Black Sabbath, Led Zeppelin, and Deep Purple.
Speed metal gave birth to Thrash metal (considered slightly more hardcore).

The New Wave of British Heavy Metal
(NWOBHM) emerged in the late 1970s, in the United Kingdom, as a reaction in part to the decline of traditional heavy metal bands such as Led Zeppelin, Deep Purple and Black Sabbath. It was also a reaction against punk, although ironically it incorporated many of British punk's innovations, and some of its aesthetic

Hard to Handle
Thrash metal is probably one of the most technically complex hard rock/heavy metal subgenres, along with death metal. The subgenre often contains a somewhat progressive musical structure as well. As a result many thrash bands, such as Metallica, Megadeth, Slayer, Testament, and Watchtower have frequently overlapped into progressive metal territory. In addition, prog metal bands such as Dream Theater have frequently cited a few of the aforementioned bands as influences


More than "Just Making Noise"
The genre relies on extremely-fast tempos, and low-register, fast or complex guitar riffs, sometimes layered with high-register guitar solos, often in combination with palm muting to create a "chugging" sound. Thrash guitar solos are almost exclusively played at high speed, as they are usually characterised as shredding, and use techniques such as sweep picking, legato phrasing, alternate picking, string skipping, and two-hand tapping. Most thrash lead guitarist are rooted in the New Wave of British Heavy Metal movement, but with more influence from progressive rock and speed metal. Many thrash guitarists are influenced by outside musical genres too, such as jazz fusion and classical music