/proc/filesystems is the file used to detect filesystems supported by running kernel. You can quickly run grep or cat command to display the list of all supported file system. nodev indicates that the file system is not associated with a physical device such as /dev/sdb1. If you see ext3 or vfat, it means you will be able to mount ext3 and vfat based file systems.
Following cat command will quickly tell you what filesystems supported by currently running Linux kernel:
$ cat /proc/filesystems
nodev sysfs nodev rootfs nodev proc nodev usbfs ext3 vfat ....
For example, if the iso9660 fllesystem not listed, you can not mount standard CD-ROM file system. To add support simply recompile kernel with iso9660 filesystem support.