Blackwell, decoded: GB200, GB300 and the 120 kW rack

Most coverage of Blackwell counts FLOPS. We'd rather count kilowatts, because the most important thing Blackwell did wasn't go faster. It made the room impossible to cool with air, and quietly retired a decade of data-center assumptions in the process.

One rack, the size of a small substation

The GB200 NVL72 binds 72 Blackwell GPUs and 36 Grace CPUs into one liquid-cooled rack carrying 13.5 TB of HBM3e and around 1,440 PFLOPS of FP4 tensor performance. It draws roughly 120 kW and lands somewhere near $2-3M per rack, with shipments that began in early 2025 (Awesome Agents, Spheron).

Hold that 120 kW number against your intuition. A "dense" data center rack a few years ago was 8-15 kW. Blackwell is an order of magnitude past that, in the same footprint. The power didn't trickle up. It stepped.

GB300: more memory, more heat

The GB300 NVL72, Blackwell Ultra, pushes per-GPU memory from 192GB to 288GB of HBM3e, lifts FP4 inference toward 1,100 PFLOPS, and runs each GPU near 1.4 kW, for roughly 50% more performance than GB200 (Tech Insider, Spheron). DGX Station systems in both GB200 and GB300 flavours began shipping to customers in March 2026, and GB200 NVL72 is now broadly available across CoreWeave, Oracle Cloud, Azure and Google Cloud (Introl).

Why air cooling quietly died

At 120 kW in a single rack, you are no longer cooling electronics, you're managing a concentrated heat source that a fan cannot keep up with. That's why GB200 ships as a liquid-cooled design, with coolant brought directly to the chips (Introl). Direct-to-chip liquid cooling stopped being an exotic option and became table stakes.

This is the part that catches operators out. You can buy the GPUs. You can even get them delivered. But if your hall was designed for 15 kW racks and chilled air, a Blackwell cabinet doesn't fit your facility, it fits a different category of building entirely.

The asset is only as good as the room

A $2-3M rack earns its keep by running near-continuously at peak. Two things stop that: thermal throttling and expensive power. A Blackwell rack that throttles because the loop can't carry the heat away is a multi-million-dollar machine performing like a cheaper one. The building isn't a backdrop to the silicon. It's a multiplier, or a tax, on every dollar of it.