The Sun UltraSPARC IV consumed 105 Watts at 1350 MHz. This for a dual core processor that could process 2 threads. Sun decided that the T1 (aka the Niagra) was going to change that. It was the first ground up redesign of the SPARC core since the UltraSPARC III. Interestingly Sun originally first attempted to develop a multithreaded process by using a pair of UltraSPARC II cores on a single die. That project was canceled in 2004, as the T1 was in development.
The T1 was designed to focus on maximum processor utilization. It contained up to 8 cores, each of which could process 4 threads. This allows the processor to be used more efficiently, as a single thread can not slow down the entire processor. All 8 cores share a single Floating Point unit. This worked well for most database type processing, as FP instructions are not very common in that type of computing. The T2 (made on a smaller process) allowed for a FP unit for each core which allowed better performance in HPC applications.
Made by TI on a 90nm process, the T1’s 279 million transistors consume only 72 Watts, a 30% reduction from the UltraSPARC IV at a similar clock speed. This is what Sun called CoolThreads Technology. Released in November of 2005 Sun was a bit ahead of their time, lower power, more efficient processors were only just beginning to become an important selling point. Interestingly, its sister project, the UltraSPARC Rk, turned out to be not so cool. Today, 10 years later, energy efficiency is one of the key metrics when measuring processor performance. With data centers having on average 50,000 computers, 30 Watts per chip adds up, quick.