“We are hitting the limits of physics in many cases” – IBM zEC12 5.5GHz

z12 MCM Layout

“We are hitting the limits of physics in many cases”  These words, spoken by an IBM engineer about the new zEnterprise EC15 mainframe do well to describe the processor that runs it.  The z12, as we’ll refer to this processor, replaces the z196 as IBM’s top performer.  The z196 ran at a slothly 5.2GHz, the fastest commercial processor in the world until now.  The z12 runs at 5.5GHz and was designed to be clocked up to 6GHz.  It is made on a 13layer 32 nm High-K process (the z196 was made on a 45nm process).  This allowed a doubling of logic and cache density.

The EC12 is designed  with single thread performance in mind.  While many systems today focus on massive parallelism, and optimizing code for multi-threading, some tasks do not work well that way, data analytics, batch processing etc, are fundamentally serial processes, so less cores, and more speed per core is far more important.  The z12 is based on a MCM (Multi-chip module) that contains 6 Processing Units (PUs) and 2 Storage Controllers (SC, which contain 196MB of L4 cache each) for a total of 8 dies on each MCM.  Each PU contains 4, 5 or 6 active cores.  The MCM is a 103-layer glass ceramic substrate (size is 96 x 96 mm) containing eight chip sites and 7356 land grid array (LGA) connections.

IBM zEC12 6-core PU – 2.75 Billion Transitors – 5.5GHz

Each PU chip has 2.75 billion transistors. Each one of the six cores has its own L1 cache with 64 KB for instructions and 96 KB for data. Next to each core resides its private L2 cache, with 1 MB for instructions and 1 MB for data respectively.

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