Your router comes with JUNOS software installed on it. When you power on the router, all software starts automatically. You simply need to configure the software and the router will be ready to participate in the network.
The software is installed on the router's flash drive (a nonrotating drive) and hard drive (a rotating disk). A copy of the software also is provided on removable media, either an LS-120 floppy disk or a PCMCIA card, which can be inserted into the router's drive or card slot. Normally, when you power on the router, it runs the copy of the software that is installed on the flash drive.
You might want to upgrade the router software as new features are added or software problems are fixed. You normally obtain new software by downloading the images onto your router or onto another system on your local network. Then you install the software upgrade on the router's flash and hard drives. You can also copy the software onto the removable media.
If the software on the flash, hard disk, or removable media becomes damaged, you can reinstall the software onto those devices.
This chapter discusses the following concepts and terminology related to installing and upgrading the JUNOS software: