IBM POWER7 details emerge

Moving on after the Power(Mac)6.

This week's Hot Chips conference saw the first serious talk about the IBM POWER7 processor, the monster square-inch sized 45nm 8-core chip with 4-thread simultaneous multi-threading (SMT) per core.

It's coming out a whole eight years after the previous 4-thread multi-threaded general purpose CPU, the Alpha 21464 EV8, was announced but prematurely killed.

The new IBM processor also has wider per-core execution at 6 ops per cycle (the Alpha was designed for 8 ops per cycle in 2000, though), a whopping 32MB shared eDRAM L3 cache on chip fed by 100 GBps dual 2-channel DDR3 controllers and 360 GBps inter-CPU fabric. It even has Turbo Mode and Power Gates just like on Intel's Nehalem. And all that is scheduled to run at 4GHz, if IBM doesn't break its promises.

IBM Power6 wasn't that old either, and in its 'plus' iteration it reached into the 5GHz realm. Yes, it was inefficient in Linpack and similar benchmarks for HPC - roughly 60 per cent achievable out of theoretical peak is really bad for a modern CPU - but it was the 'speed racer' record holder of all time.

Why did IBM make such a sudden change from Power6 to POWER7, aside from getting a massive performance gain?
Note the branding change from Power6 to POWER7 (all caps). According to sources, this had something to do with the PowerPC co-branding with Apple and expected acceptance of Power6 derivatives into the Apple PowerMac line a few years ago, before holy Steve Jobs made his about-face to kiss the hand of Miss La Intella. Remember that Power6 included full AltiVec support, needed for the MacOS but not exactly beneficial for IBM's AIX environment.

Interesting derivatives in the Power6 roadmap included entries such as Power6L ('L' as in light) and Power6UL ('UL' as in ultra light), nice matches for the Mac Pro and Imac lines respectively.

Of course, IBM did hit the thermal wall with the high-GHz Power6, just like before it Intel hit the wall with the Prescott flavour of the Pentium 4. Intel then changed the landscale, and bagged Apple away from IBM with Core 2, and IBM was left to rehash the effort.

That's the inside background of the new chip. More on its detailed works next week.