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IBM z15: A Modern Mainframe Chip

September 29, 2020

Author: Aakash Jani

IBM’s next-generation Z-series processor for mainframes, the z15, is the industry’s fastest server chip, operating at 5.2GHz. It packs 256MB of on-chip cache, setting another record. Relative to the z14, the company added two CPU cores and a handful of on-die accelerators, boasting even more custom instructions than its predecessor. The new microarchitecture generates 14% more performance than its predecessor.

The z15 mainframe system went on sale in September 2019, but architect Anthony Saporito first revealed its inner workings at the recent Hot Chips conference. The z15’s custom processor features a 3x PCIe Gen4 controller, a dedicated cryptographic accelerator, a merge and sort accelerator, and a compression/decompression accelerator. It’s manufactured in GlobalFoundries’ 14nm technology and measures 696mm2.

Most mainframes handle simple workloads such financial, utility, and government transactions, for which the z15 processor offers unique accelerators and execution units. For example, it efficiently performs financial transactions because of its fixed-point-decimal units—assuming, of course, the transactions employ fixed-point decimals, which traditionally appear in legacy software. The built-in crypto accelerator automatically handles the latest NIST-standard algorithms, including elliptic curve, thereby streamlining government adoption of the chip. Since the z15 is compatible with other IBM mainframes, recompiling software for a newer instruction set such as x86 is unnecessary. IBM offers full-stack solutions, optimizing the software to run efficiently on its mainframes.

For these customers, the z15 provides continuity with a hint of modernity. The new on-chip accelerators give a large performance boost to basic but often used functions such as compression and sorting, all while the CPUs tackle general workloads. The z15 will therefore satisfy IBM’s small but ardent mainframe customers.

Subscribers can view the full article in the Microprocessor Report.

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