My PowerBook G3 works comfortably, but my Macintosh SE can't even load a single picture. What do you think is the oldest Mac (with upgrades) that can surf the internet?
It's all really just a matter of how much work you want to put into it. It's been years now since I've done it or cared... But, I once had an Apple IIgs browsing the Internet graphically. Don't ask me to recall everything I did, it's been too many years now, and I no longer have any Apple II stuff around these days.
But, I believe there is a site somewhere that details the necessities. I'm sure a similar project could be accomplished for the older Macs as well, as there really isn't a huge difference between the capabilities of the earlier Macs and the later IIgs, other than of course CPU architecture, etc...
But, they both used similar communication protocols (serial / desktop bus), similar graphical environment (though again different CPU architecture), etc.
So, it's really a matter of how much you want to throw at it... Time, hardware, software / tweaks (either created by yourself or someone else if someone else has already done the work before).
I've seen networking them to current ethernet / cable modems with various adapters (what they called them now skips my mind - but it seems like it was similar to a short haul modem / serial to ethernet adapter). Essentially a tiny server in a box to act as a serial modem to the computer and an ethernet adapter / gateway to the network.
Then you just need the software which is either already available, or you may have to make, to establish the graphical browsing experience.
Don't expect inline pictures to appear as they do on modern machines. Usually the projects done by others in similar experiments format the HTML properly, but often have the images referenced by a link you may click on to view them separately. Keep in mind that older machines didn't have the graphical resolution of today's machines.
All you can really do, is start looking on google to see if someone's done it before with your machine, and what they used. Or, look at what others have done with similar machines and start experimenting towards a solution for yourself if you want a project.
I recall experiments / public projects for this type of thing with the Apple IIe, IIgs, and Commodore 64/128, among others that vaguely pop up... So, I would say technically, any Mac "can" do it. But, the question really is whether it's been done, and if not how much time and resources and learning are you willing to throw at it?
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I'm typing this from a 500mhz Pismo with 384mb of RAM(I have more on the way, and intend to take it up to a full 1gb) running 9.2.2 and using Classilla. I'm connected via an Airport card.
Overall, I'm finding browsing to be a pretty miserable experience. Specifically, the scrolling is very laggy, and I'm frequently finding it necessary to minimize and then expand the window to get it to appear correctly after scrolling down the page.
My 500mhz iMac and 350mhz B&W do a lot better, but I suspect that the fact that each has 1gb of RAM helps a lot. I've run into similar scrolling issues with my 800mhz iBook G3, which also currently has 384mb of RAM.
As I mentioned, I have RAM on the way-specifically several 512mb PC-133 SO-DIMMs. I intend to upgrade the Pismo to 1gb, and the iBook to 640mb(512mb+128mb soldered on). I hope this will pep both computers up a lot.
I'm probably going to install 10.4 on the Pismo this evening, so I'll see how Tenfourfox does(I expect probably not well).
Incidentally... semi related to my other post... I am familiar with the guy who heads the Classilla project. His experience in the computer industry and hobbiest market is extensive. If you really want to learn how to get old machines on the Internet, and what resources there are to accomplish it, he's definitely someone to strike up a conversation with.
He's been involved in other similar projects for vintage machines... And, I'm very familiar (or used to be very familiar) with his past projects.
It may not be a project he wants to get into, depending on his current interest level... But, he could certainly give you some good pointers and send you in the right direction.