When shopping for a new SSD or pre-built laptop, you may run into wildly different pricings that don’t immediately make sense. For example, when shopping for refurbished MacBook Pros, you’ll see that “PCIe-based flash storage” costs more than just “Flash storage”.
What you’re seeing is the difference between SATA and PCIe SSDs. One is technologically superior, but that doesn’t mean you should always prefer it. Here’s how they differ and what you need to know to make an informed decision.
Understanding SATA SSDs
SATA, or Serial ATA, is a type of connection interface used by the SSD to communicate data with your system. It was created back in 2003, which means it has had a lot of time to cement itself as one of the most widely-used connection types today.
This means better hardware compatibility. If you get a SATA SSD, it’s almost a guarantee that it will work with whatever desktop or laptop you currently have — even if that computer is close to a decade old.
The downside is in relative performance. As of this writing, SATA 3.0 is the most prevalent form of SSD, which has a theoretical transfer speed of 6 Gb/s (750 MB/s). But due to some physical overhead that occurs when encoding the data for transfer, it actually has a practical transfer speed of 4.8 Gb/s (600 MB/s).
To be fair, 600 MB/s is pretty fast and will suffice for most home users, but when compared to PCIe, it loses the race as you’ll see below. (To help illustrate how fast this is, SATA SSDs can transfer an entire CD’s worth of data in one second.)
And because of this, SATA SSDs tend to be cheaper. I imagine this will be the most important point for all but the most hardcore of users. Truth is, the difference in price is significant — almost as stark as the difference in price between SATA SSDs and SATA HDDs.
The SATA drive is half the price, which just shows that SATA is more budget friendly.
Understanding PCIe SSDs
So what is it about PCIe SSDs that make them so desirable and expensive? Does it basically come down to performance? Pretty much, yes.
You can think of PCIe, or Peripheral Component Interconnect Express, as a more direct connection to a motherboard — a motherboard extension, if you will. It’s typically used with things like graphics cards and network cards, which need low latency, but has proven useful for data storage as well.
PCIe 3.0 has an effective transfer speed of 985 MB/s per lane, and since PCIe devices can support 1x, 4x, 8x, or 16x lanes, you’re looking at potential transfer speeds up to 15.76 GB/s.
Does that mean PCIe 3.0 with 16x lanes is 25-times faster than SATA 3.0? Theoretically, sure, but you won’t find a consumer-grade SSD that comes with that many lanes. Usually you’ll be deciding between 2x and 4x, which means a maximum transfer speed closer to 3.94 GB/s.
And even so, you’re only going to notice the difference between PCIe and SATA when transferring HUGE files that take a while. If you’re playing a video game, for example, and only want faster load speeds when starting up the game or changing maps, both PCIe and SATA will be lightning fast.
Laptop users may need to worry about battery life. When browsing the web or doing any other activity that’s RAM-heavy, SATA and PCIe show no difference in battery consumption (because such activities don’t involve heavy data storage). But if you’re tranferring so much data that your SSD is constantly in use, PCIe will use significantly more energy.
One last note regarding AHCI vs. NVMe. If you ever have to choose between these two standards, go with NVMe. AHCI is older and was designed for HDDs and SATA, which means that a PCIe SSD using AHCI may not perform to its potential due to speed bottlenecks. NVMe was designed specifically for PCIe, so it performs better — but isn’t as widely compatible yet.
What Are M.2 and U.2?
M.2 (“M dot two”) and U.2 (“U dot two”) are form factor standards that specify the shape, dimensions, and layouts of a physical device. Both the M.2 and U.2 standards support both SATA and PCIe connections.
M.2 is more common by a longshot, so if you have to pick between the two and you aren’t sure which way to go, M.2 is the safer option. U.2 is mainly used for Intel 750 series SSDs and you won’t find many others that support it.
When using M.2 for a SATA SSD, performance is the exact same as using a regular SATA form factor. When using M.2 for a PCIe SSD, you’re capped at x4 lanes — but that’s more than enough for a home user. Plus, x4 SSDs are more common than x2 SSDs and not that much more expensive, so you might as well go with that.
If necessary, you can buy an adapter that turns an M.2 connector into a U.2 connector or vice versa, but such adapters may or may not fit the physical confinements of what you’re trying to do.
Which Type of SSD Is Right for You?
Now is a good time to buy flash storage any way you slice it. If you’re on a budget, go with SATA. If you want maximum performance that includes big file transfers, go with PCIe.
Both are most convenient to use in the M.2 form factor, and both are demonstrably better than HDD in terms of speed, so you really can’t go wrong.
Note that there are several other SSD-related terms you should know, like TRIM and SLC/MLC/TLC. You should also keep up with good SSD maintenance and be wary of these signs that your SSD is about to fail.
Do you prefer SATA or PCIe? If you’ve tried both, what were your experiences? Did one come out on top as the obvious winner? Got any other SSD tips? Share with us in a comment below!