Upgrading a Laptop or Desktop SSD: How to Buy the Right One

Replacing a mechanical hard drive with an SSD is the single largest performance improvement available to an older computer. Replacing one SSD with a faster SSD is usually a waste of money — and the reason is almost always a slot that cannot carry the speed.

The short answer: check your slot’s interface generation and physical size first. Buying a PCIe 4.0 drive for a PCIe 3.0 slot is the most common and most avoidable mistake in this category.

Step one: find out which slot you have

Three things decide which drives will physically work and which will actually go faster.

The size

M.2 drives come in lengths, expressed as the first four digits of the form factor:

A 2280 drive will not fit a 2242 slot. This is a physical constraint, not a firmware one, and it is the first thing to verify.

The interface generation

PCIe generations are backward compatible, which is exactly why the problem is easy to miss. A PCIe 4.0 drive in a PCIe 3.0 slot works perfectly — at PCIe 3.0 speeds. You pay the 4.0 premium for a benefit you cannot reach.

Sequence read speeds by generation, as published by drive manufacturers:

• PCIe 3.0: around 3,500MB/s ceiling
• PCIe 4.0: around 7,400MB/s ceiling
• PCIe 5.0: above 10,000MB/s ceiling, with significant heat

Your machine’s real-world figure is the lower of the drive’s capability and the slot’s ceiling, minus overhead.

The keying

M.2 slots are keyed B, M or B+M. Almost all modern NVMe drives are M-key and almost all modern slots accept them. Check the notch pattern on your existing drive before ordering if the machine is more than about five years old.

Scenario picks

Best as a main system drive in a modern machine

The Samsung 990 PRO 2TB suits a machine with a PCIe 4.0 M.2 2280 slot. It is a known quantity: a stated 7,450MB/s sequential read, a 1200 TBW endurance rating on the 2TB model, and a five-year limited warranty with a published endurance figure.

Storage & Drives

Samsung 990 PRO 2TB

Sustained write performance that holds up better than cheaper drives, a stated endurance figure, and broad compatibility. Runs warm — plan on a heatsink in a desktop.

Two practical notes: it runs warm and benefits from a heatsink in a desktop or a console, and the PCIe 4.0 speed is wasted in a PCIe 3.0 slot.

If your situation is different

• Older laptop with a PCIe 3.0 slot: buy a cheaper PCIe 3.0 drive and save the difference. Performance is identical.
• Machine with only a 2.5-inch bay: a SATA SSD still transforms it compared with a mechanical drive, and costs less
• Heavy sustained writes: prioritise a drive with a DRAM cache and a higher TBW rating over peak sequential numbers
• External use: buy an enclosure with the right interface and check whether it supports UASP for better real-world throughput

Endurance, the specification that decides lifespan

TBW stands for terabytes written: the total volume of data the manufacturer expects the drive to accept before its warranted endurance runs out. It is the honest way to compare lifespan, and it is more useful than any speed figure for a drive you intend to keep.

Rough guidance for a 2TB drive at around 1200 TBW: writing 100GB a day would take over thirty years to reach the rating. Most users will replace the machine long before the drive wears out. The figure matters most if you write continuously — video capture, virtual machines, database work.

How to choose

1. Open the service manual and find the slot specification

   You need the form factor, the keying and the PCIe generation. Write all three down before you look at any product listing.

2. Match the generation, then ignore faster drives

   If your slot is PCIe 3.0, a PCIe 4.0 drive is a donation to the manufacturer. Buy the generation the slot supports.

3. Buy the capacity you need plus one step

   Larger drives are typically faster in sustained writes and cost less per terabyte. Running out of space in eighteen months is the usual outcome of buying exactly what you need today.

4. Check the endurance rating

   Compare TBW figures at the same capacity. It is the clearest available proxy for how long the drive is expected to last.

5. Plan the migration before you buy

   Decide whether you are cloning or reinstalling. Cloning needs an enclosure or a second slot; a clean install needs your licence keys and a backup of your data.

What not to overpay for

• PCIe 5.0 drives, unless you have a 5.0 slot and a workload that moves very large files — they run hot and gain little in everyday use
• Sequential read speeds above what your interface can carry
• Heatsinks with RGB where a plain one performs identically
• Big brand premiums at the entry tier, where controllers are often shared between brands

RAID is not a backup

Worth stating plainly, because drive upgrades are when people think about this. RAID protects availability: if one drive fails, the array keeps working. It does not protect your data, because deletion, corruption, ransomware and power damage affect every drive in the array at once.

The rule that matters: three copies, two media, one off-site. A local drive plus a cloud copy plus one that lives somewhere else. An upgrade is a good moment to confirm all three exist.