The most common reason why only one USB drive can be used in Windows is due to multiple USBs connected with the same USB device signature, or disk signature collision.

If you are dealing with bootable devices and seeing this problem, we are confident a collision is the issue. If you are not dealing with a bootable device, then our information below will probably not help.

What is a USB signature collision?

A signature collision can happen on any bootable device, such as Compact Flash cards, SD cards, microSD cards, and USB flash drives. A disk signature is a unique identifier number (UID). It is a unique identifier stored as part of the MBR (Master Boot Record) for an operating system loaded on the device. The operating system uses the UID to identify and distinguish between storage devices. It is commonly made up of eight alphanumeric characters. A disk collision occurs when your operating system (Windows) detects that there are two disks with identical signatures.

For Windows 7, 8, 8.1, and 10, these versions of Windows will disable the second drive and will not allow that second volume to mount until the disk collision has been rectified. If you are reading this article, chances are, this is exactly what is happening to you.

The first thing to do is navigate to the Disk Management tool within Windows. To do this, use the search tool and type in Disk Management. This will take you to the utility that Windows offers. Here you can see your multiple devices connected. If you click or hover over the device not working you will see one of two messages:

“The boot selection failed because a required device is inaccessible” or “This disk is offline because it has a signature collision.”

What created the USB disk signature collision?

Making a bit-by-bit copy of one device to another, like using a USB duplicator, would create a disk signature collision. Because these binary duplicators copy the MBR information, that UID is also copied to the target device. Stepping forward, once those two devices are connected to the same computer, “boom” you get the collision.

Chances are, the situation you are in right now is due to a cloning process you have just completed. But don’t worry, we have the fix!

Fixing a USB disk signature collision

There are two methods for fixing the collision issue. The first solution is using DiskPart, which is a free command line tool provided by Microsoft and is found on all Windows 10 computers. This is a one-by-one process. If you have multiple devices with this problem and need to fix all of them, best to use option number two.

DiskPart Method

To launch DiskPart, simply go to the search function and type DiskPart

You now see the command prompt for DiskPart and type list disk

DiskPart will list all the storage devices connected to your computer. From this list, identify which USB is your problem device. The easiest way to determine this is to check the capacity for the drive listed by DiskPart.

Select the disk you want to change the signature ID for, for example Disk 1, which is the second disk listed (typically disk 0 is your C drive). Type select disk 1

Now that disk one is selected, type uniqueid disk and the utility will spit out the disk signature for disk 1.

Our final step is to change this value. Knowing a hexadecimal value we can use, such as A53AEBE9, type the following in DiskPart: unique disk ID=A53AEBE9 and click Enter.

With this change, you can now go into Disk Management and put the device Online. When the device is online, Windows Explorer will see the device and you can use it. There is no longer a USB disk signature collision.

If your hexadecimal value will not take, it means your MBR file doesn’t have a signature you can change. You will need to flash the device with your bootstrap code. More details on that from a previous article found here.

Another reason why option number two, below, is better is that the hexadecimal number assigned to the partition is automatic and works. There is no guessing on what hexadecimal to assign to the partition, a step you must do in DiskPart.

The second solution is downloading the free Partition Wizard and opening the software. The Partition Wizard software will automatically identify the USB disk signature collision and update the necessary MBR. Super simple!

There is more technical information about disk collision issues from Wikipedia. You can brush up on the details there if so inclined.

Japan has long been a major supplier of three key elements used in the manufacturing of NAND memory and semiconductors. Due to recent trade tensions between Japan and South Korea, these materials are becoming increasingly difficult to obtain.

Japan produces roughly 90% of the world’s supply of fluorinated polyimide and photoresists, along with about 70% of the global supply of hydrogen fluoride. This concentration places the global supply chain at risk if Japan restricts exports of these materials.

These chemicals are used by Korean manufacturers to produce semiconductors and are critical for making components such as memory chips, microprocessors, and integrated circuits.

The impact is already visible. For the first time in more than eight months, NAND memory pricing for flash drives has increased. While the percentage increase varies by capacity, the most notable jumps are in 32GB and 64GB wafers, which rose nearly 25% week over week at the time this article was published on July 25.

Japan has cited inadequate management of these chemicals by purchasing countries. Put another way, the materials can also be used in the manufacture of military weapons, and Japan claims some supplies have been diverted for that purpose. Japan’s response has been to impose restrictions on exports.

Who ultimately loses in this trade dispute? Anyone who relies on modern technology. Smartphones, processors, flash memory, circuit boards, and countless other products depend on a stable semiconductor supply chain.

For a more detailed and source-based report, visit this CNBC article.

To learn more about polyimide chemicals, a quick overview is available on this Wikipedia page.

Nexcopy is a classic entrepreneurial story—starting out in a home garage with a sale on the very first day of business. What began as a small, focused operation has steadily grown into a globally recognized manufacturer in the flash memory duplication and USB technology space. It’s the kind of company story built on persistence, product knowledge, and an unwavering focus on solving real-world production problems for customers.

Tech Company News spent time with the owner of Nexcopy, Greg Morris, to learn more about the company’s origins, its technology, and how the business evolved from a single product idea into a specialized hardware manufacturer serving enterprise, government, and industrial clients worldwide.

Here is a short snippet from that interview.

Question: What kind of technology does Nexcopy offer?

Answer: Nexcopy has a specific focus on flash memory duplication, printing, and production needs. The business started out with one product geared toward USB duplication. From that single product, Nexcopy’s business expanded into other duplication equipment such as SD card duplicators, microSD card duplicators, CompactFlash duplicators, and more recently, USB Type-C duplicator systems.

During this expansion of hardware platforms, Nexcopy also developed advanced solutions for copy protection of digital files on USB drives and mobile storage devices. These technologies were designed to help organizations protect intellectual property, control distribution, and meet compliance requirements. Several years ago, Nexcopy introduced a USB flash drive printer, which further rounded out the company’s product offering by enabling in-house branding and device customization.

Today, Nexcopy is recognized not just for duplicators, but for a complete ecosystem: devices, duplication systems, controller-level configuration, secure media, and branding equipment. That evolution—from a single garage-built concept to a specialized manufacturer with global reach—reflects a company built on deep technical knowledge and a long-term commitment to its niche.

The full Nexcopy interview is available on the Tech Company News website.

What can you get with a 3D printer and plenty of flash drives? A hedgehog USB holder. With more than 200 downloads, head over to Thingiverse to grab the 3D printable template. The hedgehog design appears to hold roughly 15 USB devices.

Just finished print a hedgehog usb holder! Much easier way to keep all of these organized then thrown in my draw! Next up is a really cool bearing system! pic.twitter.com/dbtkv6Dn97

— SteeleEgg 3D (@Steeleegg3) July 2, 2019

What do you call a bee born in the United States? A USB.

When the person who invented the USB drive dies: They will lower the coffin into the grave and realize it’s the wrong direction. Flip it, and try again.

Why do people complain about plugging in USB cables? I always connect them on my second try.

Amazon offers a USB-powered taillight: It’s used to back up your computer.

Arguing with your wife is like a USB port: You will only be right 50% of the time.

I ate my USB flash drive: It only took 1 byte.

If you are carrying around a USB stick: Do you have mobile data?

What do you call a USB stick in Russia? A “Put-in.”

The USB Type-C design is brilliant: I can’t see a downside to it.

How do you stop an elephant from charging? Take away its USB cable.

Thanks to these guys for inspiration.