Probably the wrong place to post this, and if so I apologize. I'm just trying to get a handle on what AJAX is, what it could do for me, and based on my current skills the bast way to learn about it. On that last point, I've maintained some huge and yet very primitive websites. But it started way back at a time when scripting was a nightmare. I think i got in right around the time Netscape 4 and IE 4 were the predominate browsers, and each version was taking their DOMs in significantly different directions. Building a library was almost futile, because each new browser version would break your interface to the DOM. For example, below was a test example I wrote for a long gone employer to demonstrate how a human-machine interface (HMI) for an electric substation could be done using a browser rather than a custom graphics application.

http://elfintechnologies.com/html_hmi/hmi_tst1.htm

Unfortunately if you look at this in anything but IE, it won't do anything anymore. In fact I'm shocked it still works in IE! Now this was just a demo to prove that screen control and display features could be altered without re-loading entire pages. But it still had no server side feeds. The data changing you see is just random number generators. Had my employer had any interest, my only prospect for server side communication would have been to write a JAVA applet, using something called a shared byte array object to exchange data with a server. Then, since Java can interact with javascript variables, I'd be able to complete the connection. The whole thing seemed like a daunting task.

So lately, as I've joined the ranks of the unemployed again, I'm trying to sharpen my skills, and I've seen AJAX come up again and again in employer requirements. And looking further, it SEEMS (big word) that AJAX might be a solution to such server to browser interaction, with methods I would NOT have to write or invent from scratch. Further, I get the impression that AJAX is both a javascript based methodology, and that in modern browsers, the DOMs have at least become sufficiently unified so that compatibility is much less a problem than it once was.

But maybe I have a totally wrong idea what AJAX is about, and maybe its completely the wrong tool for writing such HMIs? I am been more of an electronics and embedded systems engineer for the past decade, and I've obviously completely lost touch with web technology. So all pointers and advise is much appreciated.