# Definitions | Compute methodology
Source: https://greenpixie.com/docs/methodology/cloud-compute/definitions

Key terms used throughout the methodology.

**Accelerator.** A specialised processor attached to a compute instance for parallel workloads, most commonly a graphics processing unit.

**Active Idle.** The power a server draws while powered and running its workload software with no transactions to process, forming the lower bound of a measured power curve.

**Capacity Point.** A drive capacity for which a power figure is held, from which figures for intermediate capacities are interpolated.

**Chassis Overhead.** The electricity drawn by a server's fans, voltage regulation, and power supply losses, as distinct from the electricity drawn by the processor itself.

**Chip Vendor.** The company that designs and sells a processor, an accelerator, a memory part, or a NAND flash part. Distinct from the cloud provider that buys the part and installs it in a server.

**Cloud Provider.** A company that offers cloud computing services and solutions to businesses and individuals. In this methodology, the term refers to AWS, Azure, and GCP.

**Compute Electricity.** The estimated electricity drawn by the processor, its chassis, the host memory and drives attributable to a unit of cloud usage, and any attached accelerators, expressed in kWh.

**Compute Electricity per Usage Unit.** Compute Electricity expressed against the unit a SKU is billed in, in kWh per SKU usage unit.

**Drive.** A physical storage device installed in a server, being a solid state drive or a mechanical hard disk drive.

**Form Factor.** The physical package an accelerator is built in. Some chip vendors publish a separate rated power for each form factor of the same accelerator model.

**Hardware Thread.** The smallest unit of parallel execution a physical processor core presents to an operating system. A core with simultaneous multithreading, being a core that runs more than one thread at once, presents more than one.

**Idle Draw.** The electricity a hardware component, such as a processor, a memory module, a drive, or an accelerator, consumes while powered and available but not servicing work.

**IT Electricity Usage.** The sum of electricity consumed by the four component categories within the IT equipment of a data centre, being computation, memory, storage, and networking. Abbreviated as ITEU.

**Load Level.** A workload level on a measured power curve, expressed as a share of the throughput the server reached at full load. A load level does not measure processor utilisation.

**NVMe.** Non-Volatile Memory Express. An interface for solid state drives connected over the PCI Express bus.

**Operating Point.** The point on a power curve at which the electricity for a unit of cloud usage is calculated.

**Per-Core Factor.** The published change in the performance one core of a processor design delivers against one core of the design preceding it, at the same clock speed, as stated by the company that designs the core.

**Power Curve.** The relationship between a server's workload level and the electricity it draws, expressed as a series of measured points from active idle to full load.

**Process Node.** The semiconductor manufacturing generation a die is fabricated on, expressed in nanometres.

**Rated Power.** The thermal design power a chip vendor publishes for a processor or accelerator, being a design target for cooling. A rated power figure does not measure draw.

**SATA.** Serial Advanced Technology Attachment. An interface used by mechanical drives and by lower-throughput solid state drives.

**Server Vendor.** The company that builds and sells a complete server and submits it for power measurement. Distinct from the chip vendor whose processor it installs, and from the cloud provider that operates it.

**SKU.** Stock Keeping Unit. In cloud billing, a distinct combination of service, resource type, region, and pricing tier that appears as a line item on a cloud usage report.

**vCPU.** Virtual central processing unit. The standard unit of compute capacity allocated to a cloud instance, representing a share of a physical processor core.