Thats a nice rig. You should 'ruin' it by migrating to Win10!!! 

So wait, I am kinda confused. So I go and get a Samsung EVO 850 SSD. Is that the kind of SSD they are refering to that will 'fit' into an M.2? Is there another type of SSD that is specific ONLY to that M.2 Slot?

Thanks!

Thanks Jafo between what you posted and some research I figured out what we are talking about. Now a huge question...

Samsung is going to have 1 and 2 terrabyte versions of this type of storage. Lets shelve that for a minute...

Suppose I fork over the money and get a M.2 SSD with 512 gigs on it. I would put my OS and my 'primary' games on it. What would I need a 'cabled' SSD for if anything? I can see the use of a 2 or 3 Terrabyte platter drive for storage (porn, movies, pictures ..ect). 

I see some builds with the M.2 interface..also a regular SSD (850 EVO), and a platter drive or two. What do you put on what?

M.2 is simply faster.

SATA is a dead end technology at this point, it's expensive to make it faster, M.2 is just direct through PCI-E, which has massively more bandwidth than a SATA III interface is capable of even at the old 1.0 standard thanks to scalable lane addition.  I have a 951, it's sequential read is over 2GB/s, SATA III is only capable of around 600MB/s, the conceived SATA IV was dumped in favor of SATA Express, and would still only have doubled to about half the speed of current SSD technology.

SATA Express is probably a dead end as well.  It's a huge plug because it's a frankenstein implementation.  They're tying two SATA III ports and two PCI-E lanes together, complete with physically present SATA III outlets you can plug into.  It's almost fast enough for modern drives because of the two PCI-E lanes, but even with that it's still only good for 2GB/s.

The M.2 interface is smaller, cheaper, and at present allows for twice that at x4.  You can scale up, and PCI-E 4.0 is right around the corner with twice the bandwidth.

If you want a really fast drive, and they're expensive, you need the bandwidth of M.2 or U.2 NVME interfaces to support it.  SATA III is dogmeat by comparison.

The history of computer hardware evolution is full of superceded drive technologies.

....and not just compact casette .  Magnet drives will soon enough be on the endangered species list...

It's not like it will simply dissappear in a year or two, but cost is why it will be gone even when it's still reasonable to utilize.  PATA is still a useful technology for the modern disk drive bandwidth requirements.  With a 64MB cache, the last PATA standard in PC's can burn through that cache in half a second, at which point the typical modern drive speed isn't as fast as the interface allows.  It would be far from impractical to have UDMA ATA 200 by now, which would cover the fastest disk drives created.  They got rid of it because it was pointless to keep supporting two standards.  It's extra cost in the motherboard manufacturing, the drive manufacturing, you need to keep manufacturing two different cable types to connect them.

You can put a single lane out there for half a dozen disk drives with no one the wiser, it's much more economical than sticking drives on individual SATA ports.  That wasn't economical from the start.  We're essentially throwing away money on them, the only upside is that SATA cables and ports are cheaper than the old PATA stuff would be even with multiple devices running on a single ribbon.

It's entirely possible that we'll just end up using SATA ports over a PCI-E interface, but that means you're converting and converting is extra cost.  It's far more economical to phase out SATA entirely over the next several years, and force people using legacy drives to buy adapters.  You can run dozens of disk drives off a single X4 PCI-E slot, it's just not a big deal.

You'd have your fast stuff running off their own lane assignments, and slower physical drives running off multi-drive adapters that either stick with the existing SATA connection, or move to the cheaper PCB connection.  The frankenstien implementation is already being utilized for the U.2 connector at present, it's the SATA Express plug with 4 lanes instead of 2, allowing for two legacy SATA devices to be plugged into it instead, but this plug is enormous.  It's not a long term application you should expect to stick around, it's already wasting two thirds of the bandwidth the interface is capable of when you plug two SATA III drives into it.