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The ARM996HS was reported to use about one-third the power of a comparable synchronous ARM core—but that figure was a historical engineering estimate, not a measured result from production silicon. In a 2006 comparison, its nominal power was reported as 35% of the clock-gated ARM968E-S’s, at similar stated performance.
What “about one-third the power” means
The claim concerns one particular design comparison, not clockless processors as a category. ARM’s ARM996HS was compared with the synchronous ARM968E-S, a clock-gated core with an almost identical microarchitecture. The 2007 paper abstract describes the broader comparison as against synchronous, clock-gated ARM cores implementing the same instruction set.
In a February 2006 report, Microprocessor Report gave the more precise nominal figure: ARM996HS power was estimated at 35% of the ARM968E-S figure at 1.2 V and 25 °C. That is the basis for rounding the result to “about one-third.” It is not a claim that every clockless CPU consumes one-third as much power as a clocked one.
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What the two cores were—and how their performance compared
ARM996HS was a synthesizable, 32-bit asynchronous processor core designed from scratch using ARM’s Timeless Design Environment (TiDE) flow. Its stated compatibility covered ARMv5TE and ARM Debug Architecture. ARM described it as the first in a series of licensable clockless CPUs. The contemporary report characterized the deliverable as a firm gate-level netlist for licensees; it does not establish current licensing or availability.
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| Comparison point | ARM996HS | ARM968E-S |
|---|---|---|
| Design and clocking | Asynchronous (clockless), TiDE-designed core | Synchronous, clock-gated core; almost identical microarchitecture, according to the 2006 report |
| Nominal power comparison | Estimated at 35% of the ARM968E-S power at 1.2 V and 25 °C | Reference core for the nominal power comparison |
| Nominal performance comparison | 83 DMIPS | Comparable to an ARM968E-S running at 77 MHz |
| Stated worst-case performance comparison | Estimated at 54 DMIPS at 1.08 V and 125 °C | Compared with an ARM968E-S at 50 MHz |
The performance figures were presented as comparable at the selected operating points, not as a single like-for-like speed rating independent of conditions. The report’s implementation assumptions included a generic 0.13-micron TSMC process and an Artisan Sage-X library.
Why asynchronous control can save power
A conventional synchronous processor distributes a clock signal, which can cause circuit activity even when the task at hand does not require it. An asynchronous design coordinates operations without relying on a global clock, potentially limiting switching activity to what the work requires. The AMULET microprocessor authors summarized the principle this way: “Their asynchronous control framework has positive benefits for low-power applications because it reduces activity to the minimum required to perform a task, whereas a clock inevitably incurs wasteful activity.” The statement appears in “Power Management in the AMULET Microprocessors,” published in IEEE Design and Test of Computers in March 2001; see the University of Edinburgh record and the University of Manchester bibliographic record.
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This explains the general motivation for clockless control, but it does not identify which circuit-level changes accounted for the ARM996HS comparison or quantify their individual contributions.
Was the ARM996HS tested in silicon?
Not when the February 2006 figures were reported. ARM and Handshake Solutions were evaluating power and performance with gate-level Dhrystone 2.1 simulations using a post-layout netlist. The report said silicon results were still pending, with first samples or a small test chip expected. Accordingly, the 83 DMIPS and 54 DMIPS results—and the power comparison—should be read as reported engineering estimates from that period, not as independent measurements from silicon or modern benchmarks. The 2007 paper abstract confirms the core’s design and compatibility claims, but the available source details do not turn the 2006 estimates into silicon test results.
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