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Stepping level refers to the introduction or revision of the lithographic photomask or masks within the set of plates that generate the pattern that produces the CPU or integrated circuit. The term originated from the name of the equipment ("steppers") that exposes the photoresist to light.
Typically, when an integrated circuit manufacturer such as Intel or AMD invests money to do a stepping (i.e. a revision to the masks), they have found bugs in the logic, have made improvements to the design that allow for faster processing, or have found a way to increase yield or improve the "bin splits" (i.e. create faster transistors and hence faster CPUs). One result of some new steppings is that the CPU design is improved such that it overclocks better than others.
Many CPUs have a means of interrogating them in order to discover their stepping level. For example, on x86 CPUs executing the CPUID with the EAX register set to '1' will place values in other registers that show the CPU's stepping level.
Stepping identifiers are usually an alphabetic letter followed by a numeric number, for example "B2". Usually, the first revision of a chip is marked with "A0". A change in the letter indicates a change to the base layer mask revision and metal layers, while a change in the number indicates a metal layer–only mask revision. An analogy is the major/minor revision numbers used in software versioning. Base layer revision changes are more expensive for the manufacturer, but some fixes are difficult or impossible to be accomplished with metal-only changes to the integrated circuit.
- "From Sand to Silicon "Making of a Chip" Illustrations" (PDF). Intel. May 2009. Retrieved July 25, 2014.
- Seth P. Bates (2000). "Silicon Wafer Processing" (PDF). gatech.edu. Retrieved July 25, 2014.
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