I understand the chart you are talking about, but the problem is the only charts available are inaccurate anyway. The changes to Moodle are too rapid now to be described in such a manner. The overall core does not change that much, but other elements, like 3rd Party plugins are extending the usefulness of Moodle all the time. Also, the only charts like that I have seen are done by other organizations promoting their own product, which, of course, are completely accurate and unbiased.
-would it be a good idea for my next installations to test Moodle 1.9.19+ and after Moodle 2.3.3+ ?
_ Is it possible to transfert my course from version 1.9.19 tp 2.3.3 easily ? are there some restrictions or incompatibilities ?
If I am reading this first part right, you have a v2.3.3+ and you want to step down? No, why step backwards, there is no more support for v1.9.x not even security updates. (I think Dan Marsden's support ended December, time to move on.) There are too many differences to be a valid test. If you mean you have a v1.9.19+ and you want to restore courses to a v2.3.3+ then yes, that can happen, easily now, but no user data, which you probably do not have, just the course materials.
_ Is my dedicated small computer compatible for these versions and only for one user ? do I have to make some tuning (parameters on blocks ....) to decrease quantity/size of html files to generate ? Is it appropriate to install an html accelerator ?
Now you have lost me... Are we talking an enterprise Moodle or a standalone personal Moodle? A production Moodle can have a few users or like the OU, 250,000+ users. My test Moodles have 5 users each and I am all of them. Each user had a different role in different contexts, which can be annoying sometimes to be switching beetween the two computers I use - but it does give me some exercise..
Never used an accelerator, but might be useful. The OS you are using is pretty much irrelevant to Moodle, as long as you have some understanding of how it works, stores things, security (or any facsimile thereof), and such, you can use Moodle anywhere you can create a server. The laptop is good, plenty of RAM, disc space, but unless you allow external access, and are using a fixed IP address for it, it is probably not useful for a general server. Having said that, yes, I have done precisely that, but the laptop was not turned off and did have a fixed IP and was rebooted every Sunday after backing up the week's data overnight - smallish country school, internal Moodle very interesting experiment. Not sure what else I can say here.