SOLVED: What Do The Different Classes of Solid State Disk (SSD) Mean

At first glance all Solid State Disks (SSD’s) might look the same.  Instead of having two or three spinning disks inside small metal box (traditional hard drive), SSD’s have memory chips in a small box (or just on a tiny 2280 circuit board).  In fact there are many other factors to consider:

1. The connector – SATA or PCIe
2. The speed/type of RAM – obviously faster RAM will make for better performance
3. The controller – the small circuit board on the hard drive
4. The firmware – yes, the firmware makes a big difference

The connection type is the single most important factor:

WHAT IS SATA?

SATA is the acronym for Serial Advanced Technology Attachment is the old connector that has been in popular use from the early 2000’s to today.

WHAT IS PCIe?

PCIe is the acronym for Peripheral Control Interconnect Express is the (typically white) expansion slots on a PC.  Laptops use mini-PCIe connectors which are just physically smaller connectors that do the same thing.

ARE ALL M.2 CONNECTORS PCIe?

No, it is very possible to buy M.2 SATA SSD’s but these are fading out.  As you can see in the image to the right, SSD manufacturers can make the same SSD with either a traditional SATA or M.2 connector but both of these route to a “SATA controller”.

So M.2 does not visually tell you very much.  M.2 can connect to PCIe or SATA but SATA connectors can only connect to a SATA controller.

Today, nearly all new new PC’s and laptops use PCIe SSD drives with an M.2 connector.

To make this more confusing there are different lengths and “keys” (slots or cuts) in M.2 SSD’s.  Like the very large USB standards, the computer industry has now coalesced around just a small subset of M.2 options.  Today nearly all PCIe SSD’s are “M” or “M+B” keyed 2240’s (22mm wide 80 mm long) and 2280’s (see image at the bottom right of this article).

WHY IS PCIe BETTER THAN SATA?

SATA connectors are relatively large and bulky but most importantly their data is routed through a SATA contoller that is limited to 6MB/s where as PCIe connectors are tiny and connect to a PCH (Peripheral/Platform Control Hub) which theoretically runs 25 time faster than SATA but practically connects SSD’s at about 1GB/s .

What Do The Different Classes of Solid State Disk (SSD) Mean?

Add controller and firmware functionality into the mix and the average tech can easily get lost.  To make it much easier to understand Dell came up with a grading system called “Class”  The higher the number, the faster the disk:

CLASS	Marketing Name	Primary Market	Connector	Sequential Read/Write	Random Read/Write
10	Value	Retail Consumer	SATA	520mb/320mb	30mb/10mb
20	Mainstream	Consumer Corporate	SATA	500mb/300mb	80mb/75mb
30	Performance	Corporate	SATA	550mb/350mb	90mb/75mb
35	Performance	Pro-Consumer Corporate	PCIe M.2	800mb/1200mb	?/?
40	Performance	Pro-Consumer Corporate	PCIe M.2	1500mb/350mb	200mb/80mb
50	Performance	Corporate	PCIe Card	2100mb/1200mb	300mb/100mb

Hopefully the rest of the industry picks up this standard.

In the near future Class 10 and 20 SATA based SSD’s will disappear and we will be left with M.2 and PCIe Card connected storage drives for all but old retrofit / upgrades.

So What Type of SSD Should I Buy?

If you are still confused, just buy the cheapest SSD you can (that matches the connector you have).  Any SSD will be radically faster than traditional spinning disks.

If you have an old computer, it likely will not have an M.2 port but will definitely have a SATA port. If you have a PC or laptop manufactured after 2018 it very likely has an M.2 port.  However, you really need to check BEFORE you buy.