Revision as of 19:30, 14 September 2019

z15 is the successor to the z14, a 14 nm z/Architecture mainframe microarchitecture designed by IBM and introduced in 2019.

Process Technology

IBM fabricates its z15 microprocessors and system controllers on GlobalFoundries's 14 nm (14HP) FinFET Silicon-On-Insulator (SOI) process featuring highly-dense deep trench structures used for high-density eDRAM.

Release Dates

The z15 was launched by IBM on September 12, 2019. General availability of the z15 mainframe started September 23.

Architecture

Key changes from z14

• Central Processor (CP)
  • 2 more cores (12, up from 10)
  • Core
    • 10-13% higher IPC (IBM claim)
    • Front-end
      • Improved branch predictor
        • New TAGE predictor
        • BTB pre-buffer (BTBp) replaced by a simpler write buffer
          • single double-bandwidth port (two independentread ports)
        • 2x larger L1 BTB (8 sets of 2K rows, up from 4 sets of 2K rows)
    • Back-end
      • Larger GCT (60 groups, up from 48 groups)
        • Wider retire (12 instructions/cycle, up from 10)
      • Larger Issue Queues (2 x 36-entry, up from 2 x 30-entry)
      • 2x larger mapper (128-entry, up from 64-entry)
      • Larger integer physical register files (???, up from 120 entries)
      • Larger vector physical register files (???, up from 127 entries)
    • Execution engine
      • New Modulo Arithmetic (MA) unit
    • Memory subsystem
      • 2x larger L2 instruction cache (4 MiB, up from 2 MiB)
  • Shared L3
    • 2x larger L3 (256 MiB, up from 128 MiB)
• System Controller (SC)
  • 1.4x Larger L4 cache (960 MiB, up from 672 MiB)