I just bought a external harddrive to do scheduled backups. Could I use the same unit to backup two computers?

As Len again has said what sort of backup do you want. If it is a total physical disc disc backup which will include all partitions and be bootable then a cloning program is what you want. Clonezilla has been suggested but I would not bother with the prep and running of that when there are free programs within Windows to do the job.

One of these is EaseUs. If you just want to backup certain files then again there are several programs to do this and again EaseUs. Or just a simple "Copy and Paste" will do the job.

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