Before we begin, let us discuss why you want to upgrade the internal storage to Surface Pro X. There are two reasons to consider, with the first being the most obvious: You want more internal storage You want a faster SSD The first reason is self-evident. You bought a Surface Pro X with 128 or 256GB of storage, and you want more. Maybe you want 512GB or even 1TB. A faster SSD is less of a reason to upgrade, and should be seen as more of a side benefit. Microsoft ships Surface Pro X with a "BG3" M.2 2230 PCIe NVMe Solid State Drive Internal SSD. But Toshiba/Kioxia now has a BG4 version. On a technical level, BG4 changes from 64L to 96L TLC NAND with four PCIe lanes (instead of two) and can boost capacity to 1TB for the first time in this form factor. And while BG4 lacks DRAM, which is found on more traditional (and larger) SSDs, it does use the Host Memory Buffer (HMB) feature. Anandtech does an excellent deep dive into the improved format.