Volumes are parts of a split archive. Volumes are supported only by the RAR archive format, so you cannot create ZIP volumes. Generally volumes are used to store a large archive on several diskettes or other removable media.
By default RAR volumes have names like 'volname.partNNN.rar', where NNN is the volume number. Using -vn switch it is possible to switch to another, extension based naming scheme, where the first volume file in a multi-volume set has the extension .rar, following volumes are numbered from .r00 to .r99.
Volumes can also be solid and self-extracting. First self-extracting volume has a different (i.e. not .rar) file extension, for example, .exe for Windows SFX volumes.
It is impossible to add, update or delete files in already existing volumes. You can create only a new volume set.
To unpack volumes you need to start extraction from the first volume. If volumes are stored on non-removable media like a hard disk, you need to put all volumes in the same folder before starting extraction.
Starting from version 3.40, WinRAR stores the volume number inside of volume. You can see this number at the top of "Show information" dialog if you apply Show information command to volume. This number may be useful if original volume names are lost and you need to restore correct names manually.