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The Prospects for 128 Bit Processors ( John Mashey SGI 1995)

6 hours ago
  • Physical address sizes increase by 2 bits every 3 years, tracking DRAM density growth, and need to cover a 4:1 to 16:1 range to accommodate future memory sizes.
  • Virtual memory pressure often exceeds physical memory by at least 4x, driven by memory-mapped files and large file systems with holes, accelerating address space demands.
  • Extrapolating from current trends, a transition from 64-bit to 128-bit addressing would occur around 2043 for physical memory, or earlier (circa 2020) if virtual memory pressure increases.
  • Practical concerns like die space, wire delays, and the complexity of wide datapaths (e.g., 1024-bit) make such architectures unlikely without strong justification, with 128-bit being the more realistic near-term goal.
  • 32-bit CPUs are already insufficient for some high-end applications, while 64-bit CPUs are expected to remain adequate for a long period, with affordable options already available.

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