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Equation 1 · Part 3 · AI Accelerator Architecture in Practice: An Advanced Technical Guide

Symbol P_device

Tfleet=N⋅Pdevice⋅Usustained⋅A,T_{\mathrm{fleet}} = N \cdot P_{\mathrm{device}} \cdot U_{\mathrm{sustained}} \cdot A,
PdeviceP_{\mathrm{device}}

What this part means

a single device’s measured (not advertised) throughput on the actual workload.

Its job in the formula

PdP_device is one factor in the product that computes the quantity on the left.

Where the article explains it

where N is the device count, PdeviceP_{\mathrm{device}} is a single device’s measured (not advertised) throughput on the actual workload, UsustainedU_{\mathrm{sustained}} is the utilization fraction observed over a representative multi-hour or multi-day window rather than a benchmark’s best run, and A is availability — the fraction of time the fleet is actually up and assigned to the job rather than down for failure, repair, or checkpoint recovery.

The passage around this formula

…and the fraction of wall-clock time the fleet is not running at all. A workable capacity model has to account for both. A simple way to state the assumption explicitly is Tfleet=N⋅Pdevice⋅Usustained⋅AT_{\mathrm{fleet}} = N \cdot P_{\mathrm{device}} \cdot U_{\mathrm{sustained}} \cdot A. where N is the device count, PdeviceP_{\mathrm{device}} is a single device’s measured (not advertised) throughput on the actual workload, UsustainedU_{\mathrm{sustained}} is the utilization fraction observed over a representative multi-hour or multi-day window rather than a benchmark’s best run, and A is availability — the fraction of time the…

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A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the article section

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