Only 1 Compact Flash Card Can Be Use – Others Are Ignored

The most common reason why only one Compact Flash Card is usable when multiple Compact Flash Cards are connected is due to a device 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.

Compact Flash Card hard drive sketch

What is a Compact Flash Card signature collision?

A signature collision can happen on any bootable device, so Compact Flash Card 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 will use 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 with in 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 Compact Flash Card disk signature collision?

Making a bit-by-bit copy of one device to another, like using a Compact Flash Card 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 Compact Flash Card disk signature collision

There are two methods for going on about 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. So 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 Compact Flash Card is your problem device. The easiest way to determine this, is check the capacity for the drive listed by DiskPart.

Select the disk we want to change the signature ID for, for example Disk 1, which is the second disk listed… as typically disk 0 is your C drive. With that said, 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, it means Windows Explorer will see the device and you can use it. There is no longer a Compact Flash Card disk signature collision.

If your hexadecimal value will not take, then 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 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 Compact Flash Card disk signature collision and update the necessary MBR. Super simple!

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

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Mark McCrosky

Kicking around in technology since 2002. I like to write about technology products and ideas, but at the consumer level understanding. Some tech, but not too techie. Posting on as well.

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