AS/400 Family
It is, of course, not possible to download AS/400.
Being hardware, you can not download from the net.
If you wanted to download the AS/400 operating system (the OS400 / i5OS ) you have to consider that it is a software product bought from IBM (not freely available on the net) and that, in order to see it in action, you need an AS/400 to install it on.
It does not “run” on a PC.
If you want to acquire an AS/400 to experiment on, the advice that we can give you is to turn to dealers of used AS/400 that might have some small AS/400 to sell, suitable for educational use and at a “reasonable” price (500/1,000 euros).
Given the cost and effort, we recommend this approach only to computer consultants or professional programmers.
A modern alternative is the activation of an access to a portion of AS/400 in “cloud” click on the following link for a google search: (www.google.it/search?q=as400+cloud).
We are not aware of any free accesses in “cloud”, to an AS/400, apart from that of PUB400:
A free public space on an AS/400 for testing and training (in English).
You can register and connect to an AS/400 to practice with the environment.