Warehouse-Scale Computers to Exploit Request-Level and Data-Level Parallelism - Computer Architecture: A Quantitative Approach - page 452

FIGURE 6.13 Case study for a WSC, based on Hamilton [2010] , rounded to nearest
$5000 . Internet bandwidth costs vary by application, so they are not included here. The re-
maining 18% of the CAPEX for the facility includes buying the property and the cost of con-
struction of the building. We added people costs for security and facilities management in Fig-
ure 6.14 , which were not part of the case study. Note that Hamilton's estimates were done be-
fore he joined Amazon, and they are not based on the WSC of a particular company.
We can now price the total cost of energy, since U.S. accounting rules allow us to convert
CAPEX into OPEX. We can just amortize CAPEX as a fixed amount each month for the efect-
ive life of the equipment. Figure 6.14 breaks down the monthly OPEX for this case study. Note
that the amortization rates differ significantly, from 10 years for the facility to 4 years for the
networking equipment and 3 years for the servers. Hence, the WSC facility lasts a decade, but
you need to replace the servers every 3 years and the networking equipment every 4 years. By
amortizing the CAPEX, Hamilton came up with a monthly OPEX, including accounting for
the cost of borrowing money (5% annually) to pay for the WSC. At $3.8M, the monthly OPEX
is about 2% of the CAPEX.