HP Z620 Brochure & Specs page 58

QuickSpecs
Technical Specifications - High Performance GPU Computing
Power Consumption
Tesla K40 GPU Boost
DA – 14262 Worldwide — Version 40.1 — May 22, 2014
Base Clock: 745 MHz
Boost Clock: up to 875 Mhz
2888 CUDA cores
~235 Watts
Note 1: A 1125W PSU is required for any K40 configuration on the Z820
By default the Tesla K40 active ships with the core clock set to the base
clock. HPC workloads can have one or more characteristics as described.
When selecting one of the supported boost clocks a good strategy is to
characterize the workload with the available boost clocks. For example,
DGEMM/Linpack are extremely demanding on power. Therefore, the "base
clock" may be the correct choice when running Linpack. Some workloads in
life sciences, manufacturing, CFD, CAD, etc., may have power headroom
and can take advantage of one of the boost clocks.
HP Z620 Workstation
Page 58