PA-RISC information - since 1999

PA-8700 PA-RISC Processor

Overview

PA-8700 die
PA-8700 die, © HP

PA-8700 is an 64-bit HP PA-RISC processor from HP, released in 2001. It is based on an enhanced PA-8500 PA-RISC core with several modifications. As with other PA-8x00 processors, the PA-8700 central logic core is close to the original 64-bit PA-8000 from 1997. PA-8700 integrated significant larger on-chip L1 cache (2.25 MB) and TLB (240) compared to predecessors PA-8600 (1.5 MB and 160).

PA-8700 were followed by dual-core PA-8800 processors, the end of the line for PA-RISC in 2004. The 875 MHz version of PA-8700 was called PA-8700+, both were used in top-range 64-bit PA-RISC workstations and many servers of the early 2000s.

HP switched to a new manufacturing partner and brand-new process with PA-8700, moving from Intel to IBM fabs using silicon-on-insulator (SOI) and 0.18µ dies. This helped increase the CPU clock speed to 875 MHz. At its time, PA-8700 was one of the largest commercial processors and one of the first manufactured in SoI.

Processor details

Functional units

PA-8700 is a 64-bit PA-RISC processor that implemented version 2.0 of PA-RISC architecture. It is multi-processor capable (SMP) and four-way superscalar, so it can decode, dispatch and execute multiple instructions per cycle.

There are ten integrated functional units in the PA-8700: two Integer ALUs, two shift/merge units, two complete load/store pipelines, Floating Point multiply/accumulate units (FPMAC), two Floating Point divide/square root units plus plus MAX-2 multimedia extensions (subword arithmetic) for multimedia applications.

The Instruction Reorder Buffer (IRB) has an 56-entry instruction queue/reorder buffer for instruction scheduling in hardware by the CPU.

The Translation Lookaside Buffer (TLB) with 240 entries, fully associative and dual-ported, translates virtual-to-physical memory addresses, the Branch Target Address Cache (BTAC) has 32 entries, the Branch History Table (BHT) 2048 entries.

Cache and memory

PA-8700 have very large L1 on-chip caches. Main L1 cache is 0.75 MB instruction and 1.5 MB data, on-chip, each 4-way set associative, with quasi LRU replacement policy for instruction and data cache and data pre-fetching capability

Memory and I/O controller (MIOC) for accessing the memory and main buses is off-chip. Main memory is supported up to 16 TB with 44-bit physical addresses.

The PA-8700 is bi-endian with support for little-endian and big-endian ordering.

Speed and buses

PA-8700 processors were fabbed with up to 750 MHz and 875 MHz (PA-8750+) clock speed at 1.5 V core voltage. They attach to Runway DDR bus, 64-bit, 125 MHz, 2 GB/s peak bandwidth.

Physical

Fabricated by IBM, PA-8700 have a 16.0×19.0 mm2 die with 186,000,000 transistors (FETs) in a 0.18µ 7-layer Silicon-on-Insulator CMOS process, packaged in 544 LGA.

Performance

HP PA-8700 PA-RISC (2001) were still fast 64-bit CPUs in the early 2000s when competitors started increasing clock speeds for more performance. PA-8700 were ballpark as higher clocked as higher clocked UltraSPARC III (2001), Alpha 21364 (2001) and IBM POWER4+ (2003), faster than Pentium III Xeon (1999) and almost even with MIPS R14000 (2001).

The first Itanium Merced (2001) from HP and Intel was notably much slower than PA-8700 in integer but on par in floating point, while the second generation Itanium McKinley (2002) was faster with more than double the floating point performance.

Used in

PA-8700 processors were used in high-end HP Unix workstations and especially servers of the early 2000s.

Documentation

  1. A 900 MHz 2.25 MByte Cache with On Chip CPU (PDF, 119 KB) J. Michael Hill and Jonathan Lachman (2000: ISSCC) parisc linux
  2. PA-RISC 2.0 Architecture (.pdf) Hewlett-Packard Company (1995) parisc linux
  3. HP taps new foundry for PA-RISC processors, EE Times, August 2001
  4. PA-RISC 8x00 Family of Microprocessors with Focus on PA-8700, Whitepaper, Hewlett Packard, April 2000 archive.org
  5. PA-RISC: Betting the House and Winning, Hewlett Packard, 2000 archive.org
  6. HP REVEALS PA-8700 CHIP DETAILS, Hewlett Packard, 2000 archive.org

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