SSDs - Part 2 - Okay, which one do I need?

  • Friday, Jan 31, 2020

Are all SSDs the same? In short, no. First of all, different machines have different types of connector.

Below are the various types of drive found in most modern computers:

  • A 3.5” hard drive - this is what most desktop machines have inside them (laptops use 2.5” versions of the same thing). This uses a SATA  connection. At the time of writing, these cost about £40-50 for a 1TB (1000GB) drive. The maximum speed of these drives is around 100-200 MB/s (and only in optimum conditions, it’s often less than this).

  • A 2.5” SATA SSD - this is the most common upgrade I make to both desktops and laptops (there are no 3.5” SSDs as the internal components take up a lot less room compared to hard drives) - to fit them in a desktop, you often need a converter bracket . At the time of writing, these cost about £50-60 for a 500GB drive. The maximum speed of these drives is around 500-560 MB/s

  • An m.2 SATA SSD - this is a smaller version of the 2.5” SATA SSD - often used in more modern, thinner laptops and small desktops that don’t have the room for a larger 2.5” drive. At the time of writing, these also cost about £50-60 for a 500GB drive. Since they are just a smaller version of the same thing, the maximum speed of these drives is also around 500-560 MB/s

  • An m.2 NVMe SSD - this is the same size and shape as an m.2 SATA SSD, but uses much much faster NAND. Only relatively recent laptops and desktops have this connector, and usually expensive productivity/gaming machines. At the time of writing, these cost about £60-70 for a 500GB drive. The maximum speed of these drives is around 3400 MB/s.

    NB - It’s important when buying m.2 drives to check if the drive is single or double sided. Single sided m.2 drives only have NAND chips on one side and the reverse side is blank, but double sided drives have NAND chips on both sides of the board. This can be a problem with some slim laptops, as there isn’t room on the motherboard side to fit the drive in and the drive can get bent or damaged. It also means the drive runs hot on both sides - when in doubt, use a single sided drive for laptops. Desktop PCs are usually fine with both single and doubled sided drives, as the m.2 slot tends to be risen from the motherboard, and there is more room for cooling inside a desktop PC in general. Some desktop PC motherboards even come with a special heatsink just for m.2 drives to help them to keep cool.

It’s important to make sure that any drive you buy is compatible with the connectors you have inside your machine. A good way to check is to use Crucial’s excellent System Upgrade Checker . Just select your manufacturer and model and it will tell you what type of disk and RAM your machine uses, and whether it can be upgraded. Note, the above information is really mainly for PCs - Apple Macs and other devices have their own special caveats - see SSDs - Part 3 - Computer says no .



“So, I can just buy the cheapest SSD I can find, right?”


Inside an SSD

Unfortunately, no. Now that the technology behind SSDs is fairly well established and reliable, some manufacturers have found a way to cut corners. Good quality SSDs have what’s known as a “Cache” chip. The first SSDs that were released to market all had a cache chip - this is a small amount of dedicated RAM. This RAM acts as an intermediary between your computer and the files stored on the SSD - because RAM is a lot faster than NAND, a small amount is used to keep a record of where data is stored on the NAND flash, making read and write operations very fast. However, some manufacturers now sell drives that don’t have this DRAM cache chip. These drives are generally still faster than hard drives, but if you write a lot of data to them at once, they can actually slow down. There is an eloquent video explainer here:



In short, I’d recommend avoiding drives without a DRAM cache, especially if you are installing your operating system on them. DRAM-less SSDs aren’t much cheaper, so it’s worth paying a bit extra for one with a DRAM cache. Once you have established what type of connector your machine has, and found a reasonably priced drive with a DRAM cache - there is an excellent, and regularly updated, guide here  - you can either fit it yourself, or call Hither Green IT  to get me to do it for you. Look out for an upcoming guide on the process of installing an SSD, and how to migrate your data across from your old SSD.

And if you have a Mac, or something else that doesn’t fit the above, have a look at SSDs - Part 3 - Computer says no .