Editing iso-

{{title|iso- Comparison}}
The '''''iso-''''' prefix is used to indicate that a given difference measurement (or estimate) is reported while maintaining one or more other parameter(s) fixed.

== Overview ==
The ''iso-'' prefix means 'equal'. The word originated from ''îsos'' in Ancient Greek which had a similar definition. The prefix is used to denote that a certain reported difference measurement or estimate was done while maintaining one or more secondary parameters fixed. In other words, an iso-comparison isolates one parameter from a number of parameters that affect each-other.

iso-comparisons are important for when different parameters may positively or negatively affect the primary parameter being compared. For example, if a CPU core may deliver improved performance versus a predecessor by utilizing a more advanced [[process node]] or by making use of more advanced circuit design techniques or both. Using an iso-process comparison would demonstrate how much benefits came from the design alone.

=== Example ===
For example, "2nd-generation CPU core delivers 10% reduction in power at iso-performance and iso-process" means that the said 2nd-generation CPU core is able to achieve a reduction of 10% in its power consumption (under certain workload conditions) over the 1st-generation for identical performance level or capabilities on the same [[process node]]. In other words, this example highlights the circuit and architectural design improvements. This comparison isolates the power consumption of the core as a function of only circuit and architecture design improvements while intentionally ignoring the effects of using a different [[process technology]].

== Comparison types ==
* '''iso-performance''' - A comparison that is done at a fixed performance level (e.g., at a fixed [[SPEC CPU2006]]/[[SPEC CPU2017|17]] score).
* '''iso-power''' - A comparison that is done at a fixed power level (e.g., 1W/core)
* '''iso-area''' - A comparison that is done at a fixed physical silicon area (e.g., 1mm²/core)
* '''iso-frequency''' - A comparison that is done at a fixed frequency (e.g., at 2 GHz for all devices)
* '''iso-throughput''' - A comparison that is done at a fixed throughput (e.g., same memory or PCIe bandwidth)
{{expand list}}

== Relation to PPA ==
{{main|power-performance-area|l1=Power-Performance-Area (PPA)}}
[[File:n16 vs n28 ppa.png|right|200px|thumb|TSMC N16 vs N28 PPA in terms of iso-speed and iso-power at a certain nominal point.]]
Iso-comparison plays an important role in the advertised benefits of new [[process nodes]]. When a foundry announces a new technology node, the [[Power-Performance-Area]] (PPA) benefits of this node is usually given in terms of ''iso-power'' and ''iso-performance'' in order to demonstrate the raw capabilities of the underlying transistors. For example, [[TSMC]]'s [[N16|16-nanometer FinFET]] process was said to deliver 2x the logic density along with >35% speed gain at iso-power OR >55% lower power at iso-speed over TSMC's own [[28 nm process]]. In other words, TSMC claims that, compared to their [[28 nm process]], their [[N16|16 nm process]] can deliver over 35% speed gain at the same total power consumption, or alternatively, over 55% power reduction at the same speed. The [[figure of merits]] (FOMs) used by TSMC for those values consisted of some combination of RO inverters, NAND, and NOT gates with Fan-Out 3 (FO3). It's worth noting that while TSMC highlights the two extreme points of its process node, realistically, chip designs choose a better sweet-spot in between those two extremes.

== See also ==
* [[PPA]]