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Most hardware comparisons stop at the top three lines. That is where the interesting differences between generations live, but it is not where the expensive surprises live. Those are further down the sheet, in the fields that describe the machine as an object rather than as a rate.
Dimensions, against your actual rack
Air cooled units in this market cluster around a few chassis sizes, but the spread is wide enough to matter: depth varies by well over a hundred millimetres between families. Hydro units are different animals again, often 2U server format at around 480 by 665 by 86 millimetres, which racks densely but needs the rack depth to accept it.
Check three clearances, not one: the unit itself, the airflow or plumbing behind it, and the space a technician needs to pull it. A shelf that fits the machine but not the hand holding it costs time on every service call.
Weight, per unit and per shelf
Air units run from roughly 13 to 22 kilograms, hydro units from 14 to over 40. Multiply by units per shelf before you trust an existing rack. This matters most in retrofits, where the racking was specified for a lighter generation.
Voltage, phase and connector
This is the field that most often forces a change of plan. Air cooled machines are commonly 200 to 277 V single phase, hydro machines 380 V and up, three phase. A site built for one cannot take the other without new distribution. The connector type is worth confirming separately, because it is rarely on the marketing sheet and always on the delivery.
Operating envelope
Rated ambient temperature and humidity define where the published performance holds. Outside that window the machine does not fail, it throttles, and a throttled machine has worse real efficiency than its sheet. Altitude limits exist too and bite at elevation, where thinner air carries less heat.
Sound
Air cooled units sit around 75 dB at one metre. That is loud enough to rule out most locations with neighbours, and the figure is per machine: a room of them is not 75 dB. Hydro and immersion change this category completely, which is often the real reason to choose them rather than the efficiency.
Firmware modes
Many current machines ship with selectable performance modes, and the headline figures usually come from the standard one. Low power modes trade hashrate for efficiency and can materially change the breakeven. If a mode matters to your plan, confirm it is available on the batch you are buying and not only on a later firmware.
Run this against your own numbers
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