M.2 SSD Sizes and Keys: A Beginner's Guide

What is an M.2 SSD?

An M.2 SSD is a compact storage drive that connects directly to a motherboard slot. Unlike a 2.5-inch SATA drive, an M.2 drive is a small card that mounts flat on the board, saving space and reducing cable clutter. For a gaming PC, an M.2 SSD is a common choice for the operating system and frequently played games because of its small footprint and direct connection.

The M.2 form factor is defined by standards that specify the card's width, length, and the key notches on its connector. These standards ensure that drives fit only into compatible slots. Understanding these specifications helps you choose a drive that will work with your motherboard. For more on what an SSD is, see what is an SSD.

M.2 Card Lengths

M.2 drives are identified by a four-digit number that indicates their width and length in millimeters. The first two digits are the width, which is always 22 for standard M.2 SSDs. The last two digits are the length. Common lengths include 2242 (22 mm by 42 mm), 2260 (22 mm by 60 mm), and 2280 (22 mm by 80 mm).

The 2280 length is the most widely used in desktop gaming PCs. Most motherboards include at least one 2280 slot, and many cases have mounting points for this size. Some motherboards also support shorter lengths like 2242 or 2260, but the 2280 size is the standard for full-size drives.

When choosing an M.2 SSD, check the length your motherboard supports. The slot will have a mounting screw or clip positioned for specific lengths. If you install a drive that is too long, it will not fit; if it is too short, it may not reach the mounting point. For a deeper look at M.2 drives, visit M.2 SSD explained.

B and M Key Types

The key refers to the notches on the M.2 card's connector edge. These notches determine which slots the drive can physically fit into. There are three common key types for M.2 SSDs: B, M, and B+M.

A B key has a notch on the left side (pins 12-19), while an M key has a notch on the right side (pins 59-66). A B+M key has both notches, allowing it to fit into either a B-key or M-key slot. The key also indicates the electrical interface: B-key slots typically support SATA or PCIe x2, while M-key slots support PCIe x4.

For gaming PCs, most modern M.2 slots are M-key, designed for PCIe NVMe drives that offer higher bandwidth. Some older or budget motherboards may have B-key slots that support SATA or slower PCIe. A B+M key drive is versatile because it can fit into both slot types, but it may be limited to the slower interface of the slot. To understand the difference between SATA and NVMe, see SATA vs NVMe SSD for gaming.

Motherboard Slot Compatibility

To ensure an M.2 SSD works in your gaming PC, you need to match the key and length to the motherboard slot. The motherboard manual or product page lists the supported M.2 slot types, including the key (B or M) and the lengths (such as 2280).

Most modern gaming motherboards have at least one M-key slot that supports PCIe NVMe drives in the 2280 length. Some boards have multiple M.2 slots, each with its own specifications. For example, one slot might support PCIe 5.0, while another supports PCIe 4.0 or SATA. Learn more about PCIe generations in PCIe 4 vs PCIe 5 SSD for gaming.

If you are building a new PC or upgrading an existing one, check the motherboard's M.2 slot specifications before buying a drive. A drive with an M key will fit into an M-key slot, and a B+M key drive will fit into both B and M slots. However, the drive's interface (SATA or NVMe) must also be supported by the slot. For a guide on choosing an SSD, see best SSDs for gaming.

What to Pick for Your Play

For most gaming PCs, a 2280 M-key NVMe SSD is the right choice. This size is widely supported, and the M key ensures compatibility with modern PCIe slots. If you have an older motherboard with a B-key slot, look for a B+M key drive that supports SATA or PCIe x2.

When selecting an SSD, consider the storage capacity you need for your game library. A drive with more capacity allows you to install more games without managing space. For a growing library, a larger drive can be a practical choice. You can also explore how much SSD storage is enough for gaming for guidance on capacity.

If you are unsure about compatibility, consult the motherboard's documentation or the system builder's specifications. This ensures the drive you choose will fit and function correctly in your gaming PC. For a broader overview of storage options, see best SSDs for gaming.

What to pick for your play

Questions

What does 2280 mean on an M.2 SSD?

The number 2280 indicates the drive's dimensions: 22 mm wide and 80 mm long. This is the most common length for M.2 SSDs in desktop gaming PCs.

What is the difference between B and M keys?

The key is the notch pattern on the connector. B key has a notch on the left, M key on the right. M key slots support PCIe x4, while B key slots typically support SATA or PCIe x2. A B+M key drive fits into both.

Can I install an M.2 SSD in any slot?

No, the drive must match the slot's key and length. Check your motherboard's specifications for supported M.2 slot types. A drive with the wrong key will not fit physically.

Do all M.2 SSDs use the same interface?

No, M.2 SSDs can use SATA or NVMe (PCIe) interfaces. The slot must support the interface of the drive. Most modern gaming motherboards support NVMe in M-key slots.

What is a B+M key drive?

A B+M key drive has both notches, allowing it to fit into either a B-key or M-key slot. It is often used for SATA or PCIe x2 drives and offers flexibility for older motherboards.