I imagine LSI would be the only place to have the driver. The one you used for Windows 8 should also work for 8.1. I have to ask you though, why not replace that tape drive with an external hard drive? They're so much faster and more reliable. If you need to send backups offsite (as many businesses do), you could buy 2 or 3 drives. You can buy 1 TB external hard drives these days for $60. Just a thought.
Windows 8 had the driver for the LSI Ultra320 scsi card. But when I updated to 8.1, it went away. Since I use this to connect to my tape backup device,
it is critical to have. So, anyone have the process to install? (I found out how to install magic disc so I am hoping someone has the same process approach for the U320. I have given it a shot but so far get to the point it says a file is missing. So I seem to be close.)

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