Porteus is fast boot linux which can boot from a multiboot USB drive straight from an ISO file with persistence. This was suggested as a 'fast booting linux' version by futahorse on a reboot.pro here.
Porteus is a complete linux operating system that is optimized to run from CD, USB flash drive, hard drive, or other bootable storage media. It's small (under 300Mb) and insanely fast which allows you to start up and get online while most other operating systems are left spitting dust. Porteus comes in both 32 & 64 bit and aims to keep on the bleeding edge. It also supports several different languages and the user forum has language sections. Join the community now!
Here is how to create a Multiboot (Easy2Boot) USB drive (Flash or Hard Disk) using the 32-bit version of Porteus
1. Make an Easy2Boot USB drive by following Tutorial #72a
2. Select and quickly build and download an ISO file from http://www.porteus.org/ - Some ready-made ISOs are here. If you want to try it with persistence, try Porteus-KDE4-v2.1-x86_64.iso or the LXDE/XFCE/RazorQT versions.
3. Rename the ISO file to Porteus.iso and copy it to the \_ISO\LINUX\MNU folder on your Easy2Boot USB drive (or \_ISO\MAINMENU\MNU or any 3rd level folder)
4. Copy the Porteus-generic-persistent.mnu file to the same folder - the .mnu file is in the \_ISO\docs\Sample mnu files folder inside the Easy2Boot download.
5. Run RMPrepUSB and select the Easy2Boot USB drive
6. Click on the Create Ext2 FS button and specify a volume name and file name of porteus and a filesize of whatever you desire (e.g. 300MB) - the size is up to you and will depend on how many files you may want to add to it once you have booted. Note that the filename porteus must be all lowercase letters.
That's it - now test it by booting from a real system (or use the RMPrepUSB QEMU F11 button or VirtualBox or some other emulator).
Example grub4dos menu with 'cheat codes' for booting from an ISO file for Porteus (if you want to make your own grub4dos menu's)