IBM Power6 History and Architecture

IBM shipped the first POWER6-based systems in May 2007. Less than a year later, in April 2008, POWER6 became the processor generation on which IBM unified two previously separate server lines, System i and System p, into a single brand: Power Systems. That unification is the single most important thing about Power6's place in IBM history, more than the processor itself.

The POWER6 processor

POWER6 was a dual-core, two-way simultaneous-multithreaded chip built on a design that prioritized clock speed over core count, a different bet than IBM made with later generations. Standard POWER6 parts ran roughly 3.5-4.2 GHz depending on model, and the later POWER6+ refresh pushed some configurations as high as 4.7-5.0 GHz, remarkably high for the era. POWER6 added decimal floating-point (DFP) arithmetic in hardware, useful for financial and commercial workloads that had previously relied on slower software emulation, along with expanded vector multimedia extensions. It remained binary compatible with POWER5 code.

Alongside the May 2007 POWER6 launch, IBM introduced PowerVM as a unified virtualization brand, consolidating what had previously been separate virtualization capabilities across the System i and System p lines under one name and one set of tools, a direct precursor to the full brand unification that followed in 2008.

System i and System p, before and after

Before Power6, IBM sold two related but distinct product lines on the same underlying POWER processor family: System i (the direct descendant of the AS/400, running what was then called i5/OS, aimed at IBM's traditional midrange commercial customer base) and System p (running AIX or Linux, aimed at the broader UNIX server market). They shared silicon but were sold, marketed, and often supported as separate product families.

In April 2008, IBM merged them. Both became Power Systems, a single hardware line capable of running IBM i, AIX, or Linux, including multiple operating systems concurrently on the same physical server through logical partitioning. As part of the same announcement, i5/OS was renamed IBM i, and its version numbering changed from the old V5R4/V6R1 scheme to a simpler 5.4/6.1 format; IBM i 6.1 shipped as the first release under the new name. IBM's stated reason for dropping "i5" from the OS name was to remove the naming's direct tie to the POWER5 processor generation, since the hardware had already moved to POWER6.

What Power6 replaced

Power6 succeeded the POWER5 and POWER5+ generation, sold as eServer i5 and eServer p5 hardware. See Power5.AS400System.com for that generation's own history and current support status.

What Power7 changed

IBM announced POWER7 in February 2010. Where POWER6 had bet on clock speed with two cores per chip, POWER7 moved to four, six, and eventually eight cores per chip at lower individual clock speeds, a shift toward core count and throughput that every subsequent Power generation has continued. Power7 also introduced IBM's first server-class embedded DRAM (eDRAM) for on-chip cache, improved PowerVM further, and began the memory and I/O architecture changes that Power8 and Power9 later built on. The Power Systems brand introduced with Power6 carried forward unchanged; Power7 was a processor and hardware generation change, not another naming or unification event.

Sources

• IBM's First Power6 Box: A Glimpse Into System i 2008 Edition ... IT Jungle
• IBM POWER6 documentation ... IBM