If you’re buying a new Microsoft Xbox Series X or Series S console, remember to tuck away another $220 for external storage. That’s the price Seagate will charge for its Storage Expansion Card, a likely necessary add-on for optimal performance.

Why? While the current Xbox One X can load and play games using a conventional USB drive as storage, the next-gen Xbox Series S and Series X will only be able to play games designed for the Xbox One X from that external USB drive. Games designed and optimized for the Xbox Series X can be stored on the external USB drive. But to play them, they’ll have to be loaded onto the console’s internal SSD or a Storage Expansion Card, which offers the same performance benefits as the internal SSD.

Seagate, however, will charge $219.99 for its 1TB Storage Expansion Card, and Microsoft hasn’t yet identified any competing vendors that could help lower the price.

Microsoft’s Xbox Series X and Series S consoles ship with an internal, high-performance SSD: 1 terabyte in the Series X, and 500GB in the Series S. Both take advantage of the Xbox Velocity Architecture: Microsoft’s custom, internal SSD tech that delivers 2.4GB/s of raw I/O throughput, more than 40x the throughput of the Xbox One. The external Seagate Expansion Card offers that same capability, Microsoft said in a blog post on Thursday.

“You can play directly from the Storage Expansion Card and you will have the exact same experience and performance as if the game was running from the internal SSD,” Jason Ronald, Microsoft’s director of Program Management.

But what Microsoft has somewhat glossed over is the fact that, though consumers store their current Xbox One games on external drives, and those drives can be used to migrate existing games to the Xbox Series X and Xbox Series S, the new consoles can’t play games optimized for the Xbox Series X and S from those legacy drives. That means that a USB drive will be fine for running older, backwards-compatible games that were written for the older One X, but not the Series X.

“While your previous generation Xbox titles can still be played directly from your existing external USB 3.1 hard drives, to receive all the benefits of the Xbox Velocity Architecture and optimal performance, games optimized for Xbox Series S and Xbox Series X must be played from the custom internal SSD or a Seagate Storage Expansion Card,” Microsoft has said.

And that means buying a new, pricey Expansion Card.