A mini PC SSD upgrade starts with the exact storage slot, not just the capacity on the box. Check the drive’s length, SATA or NVMe support, and your model’s capacity and clearance limits before buying. Then decide whether you are adding a second data drive or replacing the drive that starts Windows.

That distinction matters even within the GMKtec range. Two computers can both accept an M.2 SSD while requiring different drive types. This guide helps you choose a compatible upgrade and plan what happens to your files and operating system.

Choose your upgrade route first

Start with the problem you want to solve. Running out of room for photographs is a different job from replacing the SSD that holds Windows.

Adding another physical SSD does not automatically enlarge your existing C: drive. It normally gives you a separate place to save files. Decide which folders, projects or game libraries will use that space, and use each application’s supported move or install options.

Replacing the boot drive is a separate migration task. Copying the Windows folder onto a new SSD is not a substitute for a supported cloning or installation process. SSD vendors may provide migration tools with eligibility conditions: for example, Kingston’s Acronis cloning instructions require a Kingston internal SSD. Confirm which disk is the source and which is the destination before any cloning operation.

Check the SSD specification in three parts

1. Match the physical length

M.2 describes a physical form factor. The size code tells you the width and length: a 2242 module is 22 mm wide and 42 mm long, while a 2280 module is 22 mm wide and 80 mm long. The SSD must fit the space and the supported mounting position inside your particular mini PC.

Do not assume a shorter drive is suitable simply because there is room around it. Check the model’s documented size and mounting arrangement.

2. Match SATA or PCIe NVMe support

M.2 is not another name for NVMe. M.2 drives can use different interfaces, including SATA and PCIe; NVMe is used by PCIe SSDs. A drive that looks similar, or appears to fit the connector, is not enough to establish compatibility.

Read the specification for the particular slot you intend to use. A SATA-only storage slot needs a supported SATA drive; a slot specified for PCIe NVMe needs a supported NVMe drive. Kingston’s M.2 compatibility FAQ explains why both physical fit and interface support matter.

3. Check capacity, PCIe support and physical clearance

Record the supported capacity per slot, rather than treating a computer’s advertised total as the limit for a single SSD. Check the documented PCIe generation and lane arrangement too. Do not choose solely by an SSD’s advertised maximum speed: the host connection also constrains what it can deliver.

Before ordering, confirm whether the exact SSD’s thickness and heatsink fit the computer. A large desktop heatsink is not automatically suitable for a compact enclosure. Where the product page does not settle clearance or a particular drive’s compatibility, ask for model-specific confirmation.

Two GMKtec examples: G3 and K8 Plus

The following is a comparison of published specifications, checked on 11 September 2026. It is not a hands-on test or a guarantee for every third-party SSD.

These specifications apply to the named models. G3, G3 Plus, G3 Pro and G3S are different products. Also distinguish installed capacity from expansion capacity: a supported maximum does not tell you what your selected configuration includes or whether a slot is empty.

Prepare your files before opening the case

Make a separate backup of files you cannot replace, and check that you can open the backed-up copies. Keep that backup available while you install and verify the upgrade.

If device encryption or BitLocker is enabled, confirm that you can retrieve the correct recovery key before changing hardware. Microsoft explains that hardware changes can lead to a recovery-key request in its guide to finding your BitLocker recovery key. Do not assume encryption is enabled on every computer, or that every upgrade will trigger recovery.

Use the opening and installation instructions for your exact model. Shut down the computer and disconnect its external power before working inside it, follow the documented precautions against static damage, and avoid forcing covers, connectors or screws. If the opening procedure or thermal-pad arrangement is unclear, pause and get the model-specific instructions.

Set up a new blank data SSD in Windows

This section applies only to a newly added, empty data SSD. It is not a repair procedure for a disk that already contains files or an operating system.

1. Start Windows from the existing system drive, then open Disk Management from the Start button’s right-click menu.
2. Identify the added drive by its capacity and disk details. Do not assume it is always “Disk 1”. If you cannot tell which drive is new, stop before making changes.
3. If that verified empty disk is uninitialised, initialise it. Microsoft uses GPT as the default partition style for new disks.
4. Create a simple volume in its unallocated space, assign an available drive letter and choose the file system. NTFS is the usual choice for an internal Windows data volume.
5. After setup, check that the new drive appears in File Explorer and that you can save and reopen a test file.

Microsoft’s new-disk setup instructions cover this sequence. If the new disk already has a usable volume, it does not need to be initialised again.

Do not initialise, delete partitions or format a disk containing files you need. These actions can make data inaccessible or destroy it. Microsoft’s Disk Management guidance distinguishes creating a new volume from formatting an existing one.

If the SSD does not appear, identify where detection stops

“Not showing up” can describe several different problems. Keep the hardware check separate from the Windows volume check.

• Absent from the firmware’s storage listing: review the exact model, slot, drive type and installation. Formatting inside Windows cannot fix a drive that the hardware does not detect.
• Visible in Disk Management but absent from File Explorer: inspect its status, partition and drive-letter information. Only follow the empty-disk setup procedure once you have confirmed that it contains no data you need.
• Windows will not start after replacing the original SSD: check the migration or installation result and the documented boot configuration. A blank replacement SSD does not contain Windows.

SSD manufacturer Kingston’s storage troubleshooting guidance makes these detection and setup distinctions. Use it to frame the problem; use your GMKtec model’s instructions for any hardware or firmware changes. Keep the original drive intact until the replacement boots and the required files have been checked.

Before you buy, write down these five details

1. Your exact mini PC model and current configuration.
2. Whether you are adding data storage or replacing the boot drive.
3. The target slot’s supported length and SATA or NVMe requirement.
4. Its listed capacity limit, PCIe support and physical-clearance requirements.
5. Your backup and, if needed, Windows migration plan.

If any of those details is unresolved, use the GMKtec Europe contact page to confirm the proposed SSD and slot before ordering. A precise compatibility check is the most useful first step towards an upgrade that fits your computer and your files.