Can I Have Two Operation Systems On The Amiga

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This is My Setup-:
 An Amiga D-Box towered A1200.  Hardware includes:
•   D-Box tower with 400w PSU
•   EZ VGA scandoubler and flicker fixer - allowing use of flat screen LCD monitor
•   A1200 motherboard revB with 3.1 ROMS
•   Blizzard 603e @160Mhz  PPC/68040 @25Mhz accelerator board with 160MB RAM (1 x 128, 1 x 32)
•   BVision PPC graphics card with 8 megs graphic memory
•   PCMCIA Network card (LAN) and PCMCIA right angled adaptor
•   2 x 20 GIG HD
•   CD RW
•   Floppy Drive
•   Amiga trackerball mouse

Is it Possible to have two operation systems on the Amiga tower which would be Amiga OS 4.0 and Amiga OS 3.9

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I have only just got back into the Amiga I have a Amiga 1200 which I have just go out of the loft The question I want to ask is it easy to put another operating system (3.9) on the Amiga I have OS4 running do I have to reinstall OS4 can I do this with OS4 running.