From MEPIS Documentation Wiki
It is possible to test whether MEPIS works on your computer — without changing your current operating system or altering any files on your hard disk drive. The MEPIS Live CD boots your computer right from the CD without accessing the hard disk, and it copies a virtual filesystem into RAM which acts as the center of a temporary operating system for the computer! When you end your Live CD session, everything about your computer is back to the way it was, unchanged. This provides a number of benefits:
- It enables you to run MEPIS on your computer without installing it.
- It allows you to determine whether MEPIS is compatible with your hardware.
- It helps you to get a feel for how MEPIS works and to explore some of its features.
- You can decide whether MEPIS is what you want without permanently affecting your current system.
NOTE: Because the entire system is being run from a combination of RAM and the CD, MEPIS will run more slowly in a Live CD session than if it were installed on the hard drive. Performance in a LiveCD session will be greatly influenced by how much RAM you have installed. But even the most up-to-date CD-ROMs transmit data only about 10% as fast as an ATA-100 hard disk drive. So even with a lot of RAM there will be some sluggishness during CD disk-reads. See Fromiso for a way to get speedup.
Some unusual hardware that requires specialized drivers or custom configuration may not work in a session where permanent configuration files can't be downloded and installed. But for most average computers, that won't present a problem.