The original name for the ISeries still in use by many programmers and administrators. The "AS" originally meant "Application System." First sold in 1988, it was the direct successor to the System/38.
The original AS/400 hardware was based on a 48-bit proprietary CISC CPU, but was replaced in 1995 with a 64-bit PowerPC RISC CPU. Even though the hardware platform changed, very few programs needed to be changed or even recompiled.
Silverlake was the codename for the AS/400 project before it was released. It was considered by many to be one of the worst-kept secrets.
Also see the AS/400 write-up in [Wikipedia http://en.wikipedia.org/wiki/AS/400]
Also see Wayne Evans history page at http://www.woevans.com/My_Homepage_Files/Page3.html