Introduction and Moore's Law Flashcards
What is the basic idea of Moore’s Law?
A now-defunct observation that essentially said that hardware power will double every 1-2 years into infinity, through the packaging of more transistors into a single chip and therefore the reduced price of transistors.
DEFINE: The digital abstraction
The idea of making software knowledge non-reliant on hardware-specific capability (i.e. caching, manycores, …) for performant code.
Why wasn’t performant software a huge area of focus before the 2000’s?
Moore’s Law (or a variation of it) meant hardware would scale to lift the performance of the software, so incremental software gains would be lapped by hardware… until the end of Moore’s Law.
Moore’s Law is typically cast as “Performance doubles every X months.” What’s a more accurate description?
“The number of transistors per unit cost doubles every X months.”
DEFINE: Dennard Scaling
The theory that power density stays constant as transistors get smaller, as expressed by the following equation:
Power = Capacitance x Voltage^2 x Frequency
What is missing in the following equation, and what is this equation for:
_____ = Capacitance x _____^2 x Frequency
Dennard Scaling. Power, Voltage
In regards to Dennard Scaling, what elements of the equation would ideally be decreasing, constant, and increasing?
The equation is Power = Capacitance x Voltage^2 x Frequency.
Power: Remains constant. We’d like to increase it but there is a limit thanks to thermal considerations.
Capacitance: Decreases. When transistors shrink, they require less charge to have the same power, so we want to shrink them.
Voltage: Decreases. We can operate the transistors that we want to shrink with less charge. The problem here is leakage, but this was a source of power depression for a while.
Frequency: Increases. This is clock speed, and with more clock speed we improve performance. We want to push this as high as it goes.
In regards to Dennard Scaling, why can’t we infinitely increase power to improve frequency?
Thermal concerns. We get “thermal runaway,” where a positive feedback loop on temperature causes permanent damage.
In regards to Dennard Scaling, why can’t we infinitely decrease capacitance and voltage to improve frequency?
Physics complications in regards to strict size limits and electrical engineering complications.
What’s usually missing from the Dennard Scaling equation?
Leakage: … + Voltage x Leakage
This is also known as Static Power, whereas the original equation represents Dynamic Power.
When Dennard Scaling ended around 2006, why did Moore’s Law (as generally known) hold for a while afterwards?
Multicore systems.
DEFINE: The Utilization Wall
The practical limit on how many gates in a chip can be active at a time thanks to thermal issues.
When Moore’s Law ended, what two solutions were the only way to keep performance improving?
Solution 1: Write software more efficiently with underlying knowledge of architecture.
Solution 2: Build and use hardware best suited for a given task, ending general-purpose cores’ dominance.
TRUE/FALSE: Moore’s Law boils down to getting faster performance out of the same power.
TRUE.
TRUE/FALSE: Capacitance hit its limit because of leakage.
FALSE. This is Voltage’s limit, Capacitance hit a physical limit with gate-oxide thickness.
