A Second Drive for Your Computer: How Many M.2 Slots You Have and How to Set Up a New Drive

The short answer: Adding a second drive involves three steps, and the first one is research. Find out what your computer can physically accommodate — how many M.2 slots the motherboard has, how many SATA ports are available, and how many bays there are for 2.5″ and 3.5″ drives. Account for shared lanes: on many motherboards, using an M.2 slot can disable a specific SATA port, causing an existing drive to “disappear” after the upgrade. Then set up the new drive in Disk Management: Initialize Disk → GPT → New Simple Volume → NTFS and a drive letter. Do not move the operating system to the second drive; leave it where it belongs.

First, find out what the computer can actually accommodate

Opening the case and taking a look is faster than searching online. Write down four numbers:

• how many M.2 slots there are and which lengths they support (2280, meaning 80 mm, is the most common; shorter 2242 and 2260 drives are mainly found in laptops);
• how many SATA ports the motherboard has and how many are available;
• how many bays the case has for 2.5″ and 3.5″ drives, and whether an unused power connector from the PSU can reach them;
• which interface the M.2 slot supports — PCIe/NVMe only, or SATA as well.

That final point is responsible for many unnecessary product returns. ASUS gives a clear example in its support documentation: the M.2_1 port supports both SATA and PCIe, while M.2_2 supports PCIe only. If you insert a SATA M.2 drive into a slot like that, the computer will not detect it at all — even though neither the drive nor the slot is faulty.

Space is tighter in a laptop, and there are three possible options: a second M.2 slot, which thin laptops generally lack; an available 2.5″ drive bay; or a caddy replacing the optical drive. Before buying anything, check the service manual for your model. Some laptops have space for another drive but lack the mounting bracket and data connector.

M.2 slots can disable a SATA port

This is the most common surprise during the entire upgrade. The lanes used by drives to communicate are limited, so motherboard manufacturers often make some M.2 slots share resources with SATA ports. Install an M.2 drive, and one specific SATA port stops working.

ASUS describes a specific example in its support documentation: the M.2_1 port is shared with the SATA6G_1 port, and if you connect a device to both, SATA6G_1 is disabled — the computer then sees only the drive in M.2_1. The solution is not to return the drive, but to reconnect the older drive to another port, such as SATA6G_3.

You cannot guess which ports your motherboard shares or infer it from another model. This information is always found in the user manual for the specific motherboard, usually in a table next to the connector diagram or in a note below it. You can download the manual from the manufacturer’s website using the exact motherboard model printed on the board or shown in the BIOS. The practical consequence is simple: if you plan to use three or more drives in one computer, check the resource-sharing table before buying them. Otherwise, a system that appears to support five drives on paper may only run three in practice.

2.5″ and 3.5″ bays: the unexciting but reliable option

A conventional SATA drive is still the most affordable choice when you need a large amount of storage. You will need two things that are usually not included with the drive: a SATA data cable connected to an available motherboard port and a power connector from the PSU. There are also a few recurring service issues to keep in mind:

• A 3.5″ drive is a mechanical device with spinning platters — it is noisier, generates heat, and does not tolerate impacts. It should be firmly screwed into the case, not left lying on the bottom.
• A 2.5″ SSD requires an adapter bracket to fit into a 3.5″ bay.
• Connect the cables while the computer is switched off and unplugged. After connecting them, check that each plug is firmly seated — a loose connection causes intermittent failures that can look like a dying drive.
• If you mainly want another drive because you are running out of space, first read how to free up disk space in Windows 11. Sometimes a cleanup is enough and no purchase is necessary.

Set up the new drive in Disk Management

A new drive does not automatically appear in File Explorer. Microsoft states this directly: until you initialize the drive, it is not available in Windows. The procedure is short:

1. Type create and format hard disk partitions into the search box, right-click the result, and select Run as administrator.
2. Find the new drive. If its status is Offline, right-click it and select Online.
3. Right-click the drive → Initialize Disk. Make sure you have selected the correct drive, then confirm the partition style; the default GPT is also the correct choice for a new data drive.
4. Right-click the unallocated space → New Simple Volume. Use the full capacity, assign a drive letter, select NTFS as the file system, and finish the wizard.

Why GPT? According to Microsoft, it supports more than four partitions and drives larger than 2 TB, whereas MBR is limited to 2 TB and is not recommended for larger drives. Converting between partition styles is also possible only on a drive without partitions or volumes, so choosing incorrectly today can mean deleting data tomorrow.

One warning deserves bold type: initialization and formatting are destructive operations. Microsoft’s guidance for drives containing data is clear — back up first, then initialize. If an unknown drive containing data you need appears in Disk Management, do nothing and have it assessed; data recovery in Brno explains what to do in this situation.

What to move to the second drive

A second drive is most useful as storage for data, not for the operating system. Leave Windows, applications, and your user profile where they are. Move files that take up a lot of space but do not require the fastest response times, such as photos and videos, project archives, game libraries, virtual machines, and phone backups. Windows provides a dedicated setting for this: under Settings → System → Storage, you can choose the default location for new apps, documents, music, pictures, and videos, so new files are saved directly to the second drive. However, this setting only affects newly saved content. Move existing folders manually and confirm that the files open correctly after the move before deleting the originals. For folders synchronized with the cloud, first read why OneDrive is not a backup; moving files outside a synchronized folder can remove them from the cloud.

A second drive, or a replacement instead?

If your goal is to make the computer faster, adding a second drive will not achieve it — that requires replacing the system drive. Migrating to an SSD without reinstalling explains how to preserve your programs and settings, while installing an SSD in an old laptop considers whether the upgrade is worthwhile for an older machine.

Two drives in one case are not a backup

A copy stored on a second drive inside the same computer may look safe, but it is not. A power surge, PSU failure, ransomware, theft, or an accidentally deleted folder can affect both drives at once. A second drive provides convenience; it only becomes a backup when another copy exists outside the computer — see the 3-2-1 backup rule for the basic principle. Back up your data before moving anything. If the upgrade reveals that the original drive is in worse condition than expected, read how to recognize a dying SSD.

What to bring to the repair shop

If you do not want to install the drive yourself or are unsure about shared slots, bring the entire computer along with the drive if you have already purchased it. For a laptop, provide the exact model number — this determines whether there is any room for a second drive. It is also useful to tell us how much data you want to move and whether the computer should handle backups as well.

We do not promise the scope of the work or the price in advance; we confirm both only after inspecting the computer. We supply and install drives for businesses in Brno and the surrounding area, although different terms apply to multiple workstations than to a single computer. Arrange an appointment through the booking form or call 774 777 774. In the description, include the make and model of the computer or motherboard and explain what you expect from the second drive.

Sources

• Microsoft Learn: Initialize new disks
• Microsoft Learn: Convert a disk to the GPT or MBR partition scheme
• Microsoft Learn: Disk Management overview
• Microsoft Learn: Change a drive letter
• Microsoft: Storage settings in Windows
• ASUS: Hard drive or SSD cannot be found after the motherboard is powered on