Racks and sites

A rack has two numbers, not one: how many units are occupied, and how much of its circuit is already drawn. A cabinet can be half full and take nothing more, and that is the most common way a machine room is discovered to be finished. The table is sorted by the higher of the two — sorting on unit occupancy alone puts the over-drawn cabinet below one with a circuit to spare, which is exactly backwards for the only question the list is read for.

Circuit utilization

Rack power divided by amps × volts × 0.8.

The 0.8 is NFPA 70 §210.20(A): a continuous load — three hours or more, which every server is — is planned at 80% of the circuit rating. The derating is already in the denominator, so an 80% warning threshold on this column is 80% of the already-derated figure.

Without a rack register there is no circuit utilization at all. Amps and volts per rack come from no automatic source, so they are recorded separately. A rack with no record shows "Rack registration required" instead of a number — not a defaulted guess, and not a zero.

The table columns

Column	What it says
Rack	The rack name. Clicking opens the elevation beside the list
What binds	Power or units — the higher of the two percentages
U utilization	Occupied units out of the rack's height
Circuit utilization	Draw against the permitted continuous load
Free run	The largest contiguous free run, not the total free units
Power · Power free	Cumulative average draw, and what is left before the limit
Devices	How many physical servers are recorded in the rack
Circuit	Amps and volts, from the rack register
Weight limit	The permitted static load, as recorded

The free run is the column that cannot be given up. A rack with 22 free units spread over eleven two-unit gaps cannot take a four-unit chassis, and a fill percentage hides that completely.

Rack height comes from the rack register. With no record the screen assumes 42 units, and deliberately so: EIA-310 standardizes the unit, not the cabinet height, which makes this a convention rather than a standard.

Weight

The rack's weight limit is recorded; the actual load is not computed. The inventory holds no chassis weight, and inventing a figure per model is exactly the number someone would plan a raised floor around. The card prints the limit and states explicitly that the load cannot be computed.

The elevation and the table beside it

Clicking a rack opens two alternating views of the same thing: Elevation and Table.

The drawing does not mirror in Hebrew. A rack is a physical object: unit 1 is at the bottom in every country, and the machine at unit 1 is the machine at unit 1. What does move is the unit-number gutter, which sits on the reading-start side — the right in Hebrew, the left in English — so the reader meets the axis first.

The table beside the elevation is not a fallback but a peer. It is what a screen reader and an export consume, and it is the only one that answers "where is there a four-unit run": its rows are U from, U to, height, server name and status, including the free gaps.

By site

Below the list is a roll-up per site: how many racks and devices it holds, total power, occupied units, the tightest rack, how many of the racks are electrically registered, and how many systems sit in the room.

Cooling is derived from power: watts × 3.412142 = BTU/hr, and 12,000 BTU/hr is one ton of refrigeration. Both conversions are definitions, which is why they are tagged as a standard.

When there is no physical placement data

If no server in the inventory carries a rack and a unit, the screen does not render an empty table — it explains that rack and unit are fields with no automatic source: a person puts a machine in a cabinet, and nothing on the network knows which room it is in. They arrive from a rack-list import or from manual entry on the host record.