The major reason I upgraded from Xbox One to Xbox One X was for 4K UHD resolution. And the main reason I upgraded from Xbox One X to Xbox Series X was for its SSD. Now that I've retrofitted an SSD to my Xbox One X, is it just as good as a Series X? The answer is no. Xbox Series X still vastly outperforms the Xbox One X even with SSD.

Even Faster Loads

As a representative data-intensive task, I loaded up Forza Horizon 4 and traveled between the main content area (UK mainland) and one of the expansions (LEGO island.) Xbox One X on its original HDD required about 44 seconds to switch maps. Now that it has an SSD, load time has been cut by more than half to 21 seconds. A great improvement but pales in comparison to Xbox Series X which takes only 14 seconds to make the same transition. I'm not sure how much of that is the faster NVMe-based data bus for Series X SSD and how much is its faster processor, but it's clearly and measurably faster. 44 seconds is long enough to get up from the couch and get a beverage, 14 seconds is barely long enough to pick up my phone to check messages. As this was one of the lengthier transitions in the game, in practice it means I'm rarely left waiting on a Series X while playing.

Quick Resume

Xbox Series X is superior to One X in many other ways, I'm enamored with its higher framerate which arrived simultaneous with HDMI spec to take advantage of it. I even bought a TV to go with Series X, a LG OLED with beautiful picture and terrible software. But back to the subject of load times: "Quick Resume" is a new feature. It suspends a game when the user switches away and, when the user is ready to pick up that game again, reloads the suspended data. Xbox One X required about a minute to start Forza Horizon 4 from stock HDD. With my SSD upgrade, FH4 loads in about half the time: 31 seconds. And that's only up to the introduction screen, it takes another ~60 seconds (HDD) / ~30 seconds (SSD) before I'm driving. In contrast a Series X with Quick Resume can take me from home screen and into the driver's seat in about 8 seconds. I find this absolutely astonishing and I'm a huge fan of this new feature.

TRIM

A final note on storage: I don't know if Xbox One X issues TRIM commands to the SSD as data come and go. This was important for SSD longevity (Wikipedia has more details) and requires operating system support. Since it never came with a SSD, there's no reason for Xbox One X to issue TRIM commands. On the other hand, low level disk code is probably shared between all Xbox variants, including the SSD-equipped Series S and Series X that would benefit from TRIM. And since TRIM is ignored by older drives that don't understand it, there's no reason for them to put in extra effort to disable TRIM on older consoles. And finally, various manufacturers (including Crucial who made the drive now living in my One X) claim that their SSD firmware is now advanced enough they don't need TRIM to obtain optimal performance. I'm not sure I believe that, and I don't know of any way to tell if TRIM is happening, but SSDs are now cheap enough I'm willing to continue this experiment.