Magnetic tape is extremely slow, but also also extremely cheap.
Is there any way to use tape to backup a computer?
What is exactly this?
A cartridge? A drive?
Are there any inexpensive way to connect those tapes to a normal desktop?
It says cartridge on the photo so that is the answer. It is an LTO4 cartridge that holds 800GB uncompressed.You need an LTO drive of some sort and likely a SCSI or SAS card to connect the drive. That will drive up the price a bit. I have used such drives in a workstation but not cheap to do.
Using a USB3 or eSATA drive would be fast and much less expensive.
Tape has many uses still but I would suggest not practical for most desktop systems. More info about what you are doing would perhaps get a more detailed answer.