OK lately a lot of people I've been talking to in regards to my RX-7 all say "oh yea that thing has a twin turbo setup right?"
When I mention the term sequential no one has an idea what I'm talking about. Here is a brief run down of what each really means:
Twin Turbo Setup = Two identical turbos running in parallel.
Sequential Turbo Setup = Two turbos (usually run in-line) one which is smaller with less lag that spools up quicker and provide power in the lower RPM range, and the secondary larger turbo that spools up to provide bigger boost and more power at the higher RPM range.
Here are pictures of both: Twin turbo first