With the Surface Pro 4, Microsoft's surprising hybrid tablet journey finally makes sense. It's as if Microsoft was laser-focused on fixing the issues we had with the Surface Pro 3. We liked that device quite a bit, but its Type Cover was endlessly frustrating, with a sloppy keyboard and wonky trackpad.
https://www.engadget.com/2015/10/21/surface-pro-4-review/
Surface Book owners complaining about slow SSD speeds. Problems have been reported since the end of October, and here’s what some users have been complaining about on the Microsoft support forums: I am experiencing very poor SSD writing performance in my Surface Book. It’s i5 dGPU 8GB RAM and 256GB storage model. Installing applications and copying files have been really slow. Windows 10 is updated to the latest.
http://windowsreport.com/slow-ssd-surface-book/
The Surface Pro 4 builds on the best parts of the Surface Pro 3, and it finally delivers a solid typing experience with the revamped Type Cover (which is unfortunately sold separately). It's the ideal hybrid tablet in practically every way -- it's as light as a tablet, but as productive as any laptop.
https://www.engadget.com/2015/10/21/surface-pro-4-review/
External Disc Performance on the Surface Pro 3. I bought a Surface Pro 3 a couple of months ago, and probably like everyone else who buys one for themselves, thought long and hard about my options. I use my laptop as my main machine, so use it for development and everything else. I wanted the Surface Pro 3 to be my main machine. I was replacing an i7 laptop, so I only really considered the i7 SP3. So the next decision was 256gb or 512gb SSD. The difference in the UK is a hefty £310 - £1649 as compared to £1339 (neither of which is particularly cheap).
http://www.gui-innovations.com/Blog%20Posts/external-disc-performance-on-the-surface-pro-3.html
There are three basic SSD interfaces: SATA, M.2/U.2 and PCIe expansion card (which may internally have a M.2/U.2 device). The type of interface chosen depends on the available ports on your motherboard. If you are creating a new build then you have flexibility.
http://www.tomshardware.com/answers/id-3113844/types-ssd.html
Extremely slow SSD in Surface Book. I am experiencing very poor SSD writing performance in my Surface Book. It's i5 dGPU 8GB RAM and 256GB storage model. Installing applications and copying files have been really slow. Windows 10 is updated to the latest.
https://answers.microsoft.com/en-us/surface/forum/surfbook-surfstorage/extremely-slow-ssd-in-surface-book/4267a139-0603-4a91-9cec-97982d71d511
If you need more storage space, you can use one of the following storage options: 1  OneDrive: Save your files on OneDrive—free cloud storage that comes with your Microsoft account. 2  MicroSD card: Insert a microSD memory card into the microSD card slot on your Surface.
http://www.microsoft.com/surface/en-us/support/storage
There are two types of M.2: M.2 SATA and M.2 PCIe. M.2 SATA is no different than regular SATA SSD in terms of speed. It's just smaller. M.2 PCIe is the smaller version of regular PCIe SSD, but I think we aren't able to keep the speed of M.2 PCIe the same.
http://www.tomshardware.com/answers/id-3113844/types-ssd.html
Surface storage. Pre-installed software and apps use a significant amount of the internal disk space on your Surface. Applies to. Surface Studio, Surface Book, Surface Book with Performance Base, Surface Pro 4, Surface Pro 3, Surface 3, Surface Pro 2, Surface Pro.
http://www.microsoft.com/surface/en-us/support/storage
By Feb. 18, 2015, 12:10 p.m. Until recently, PC buyers had very little choice for what kind of file storage they got with their laptop, ultrabook, or desktop. If you bought an ultrabook or ultraportable, you likely had a solid-state drive (SSD) as the primary drive (C: on Windows, Macintosh HD on a Mac). Every other desktop or laptop form factor had a hard disk drive (HDD).
http://me.pcmag.com/storage-devices/1009/feature/ssd-vs-hdd-whats-the-difference
what type of storage  surface laptop ssd slower
At 256GB storage surface, SSD laptop get slower.