I have to install SL 5 on my pc. The problem is: my pc doesn't have a dvd player and thus I have to make a bootable USB. No problems there too. I can make a bootable USB with one iso file in it. So I mounted the 2 iso's I got from official scientific linux 5 link.
Before proceeding please take a moment to understand the Scientific Linux releases and what you can and can't do while upgrading from one to another: https://www.scientificlinux.org/documentation/faq/faq-releases/
SL5 is no longer supported/distributed. Please download and use SL6x or SL7x:
Prefer the 7x release unless you explicitly need 32bit.
Now that yo have the correct ISOs, in order to make a bootable USB media you need to use the
dd command or similar or any other graphical tool for the purpose like Rufus for Windows. In Ubuntu MKUSB is strongly recommended:
sudo add-apt-repository universe # only for standard Ubuntu sudo add-apt-repository ppa:mkusb/ppa # and press Enter sudo apt-get update sudo apt-get install mkusb mkusb-nox usb-pack-efi
MKUSB is quite user-friendly. For detailed informations please refer to the quick start manual.
Now that you have a SL live media just boot from it and either run live or install in dual-boot.
If you are uncertain about how to do the installation, and/or you want to install the system only temporarily, and/or you want to be able to configure multiple hosts inside a private network (or whatever other excotic fancy floats your boat), then installing in a virtual machine environment may be a better option than trying to install a dual boot system.
Using, for example, Oracle's VirtualBox, it's easy to set up a virtual machine with the disk size, memory requirements etc. that you need (bounded by the host machine's available resources, of course). You additionally do not need to burn a CD-ROM or DVD as the ISO file may be mounted in the guest OS's virtual CD-ROM drive.
If you mess up, just delete the machine and start over. If you're happy with a setup but plan a big upgrade of it, make a snapshot so that you can get back to a working system if you mess up with whatever you're about to do.
I run three OpenBSD machines on my single Windows laptop, inside VirtualBox. I seldom use Windows for other things than for web browsing and Slack. The virtual environment is where all my work happens.