I recently was given a small USB flash drive as an advertising gimmick. When I plug it in, only one drive appears: a CD drive with 42kb used (just an autorun.inf file which launches the manufacturer's website). I know U3 drives also appear as CD drives, but their uninstall utility only works for their own drives.

How can I make it appear as a USB drive instead? Conversely, if I wanted to do the same thing for myself, how would I make it appear as a CD drive?

I'm sure it can be done programmatically, or else the uninstall program wouldn't work.

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4 Answers

This is done in hardware. The device identifies as a composite device containing two children - one for the CD drive and one for the removable storage drive.

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Ok, there is 2 questions here :

1) How can I make it appear as a USB drive instead?

It's depends on device itself. I can see 2 options.

• Device support writing, but represent itself as CDROM and read only. In this case you just need to tweak the device descriptor and you will get working storage device.
• Device does not implement write and nothing can be done.

By tweaking device descriptor i mean filter driver that will receive device descriptor and will pass a modified one to Windows. Writing filter driver is not very hard and you can find an examples of filter driver in Driver development Kit. A basic understanding of USB protocol will be needed as well.

2) Conversely, if I wanted to do the same thing for myself, how would I make it appear as a CD drive?

Basically same, filter driver that will change the device descriptor to be recognized by CDROM device, but in additional once Windows will recognize CDROM it will send additional SCSI commands to device. Ideally device will just return unsupported command and it's OK, but from my experience most devices are not generic enough and the behavior will be undefined. In this case you will need additional filter driver that will catch this additional commands and will complete the commands without actually sending them to device.

P.S
My answer assume that you don't have access to device firmware, If you do have access to firmware it's really easy to accomplish by modifying device descriptor and making sure that not supported commands are handled correctly.

P.P.S
I don't provide any links to resources since i don't think that practically you going to implement this. If I'm wrong let me know and i will provide relevant resources. Ok one link with general information

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Hey guy, I have done with my usb FD serveral times to make it into 2 devices CD and usb. The only thing you must do is download chipgenius then run it,wait for it to identify your usb then go to search your usb firmware tool. If you get the correct one i'm sure there will be no problem. I had done that and turned my usb into hiren boot cdrom, and when boot from bios you no longer choose your usb name but choose usb-cdrom option.

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The flash drive has been partitioned and formatted using the cdfs file system, use the dos command diskpart to look at and delete\create the partitions as fat fat32 or ntfs

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