I'm not sure that was the use-case. With pre-DHTML HTML4, there really just wasn't anything on a page that could continue to interact with the server after the page finished loading. So, presuming the button was for your described use-case, what would the difference be between "going offline" and just... not clicking any more links? (It's not like Netscape could or should signal your modem to hang up — Netscape doesn't know what else in your OS might also be using the modem.)
These browsers were born in the era of dialup Internet that had per minute charges and/or long distance charges. At the very least you were tying up your family's phone line.
Basically it's like paying for every minute your cable modem is plugged in.
For the feature itself: Netscape had integration with the modem connectivity for the OS and would initiate a connection when you tried to visit a remote page. Offline mode let you disable automatic dialing of the modem.
I ran a BBS, my friend :) I'm quite familiar with modems. I just never used Windows (or the web!) until well past the Netscape era, so I'm not too familiar with the intersection of modems and early web browsers.
> Netscape had integration with the modem connectivity for the OS and would initiate a connection when you tried to visit a remote page.
That's not "integration with modem connectivity", that's just going through the OS's socket API (or userland socket stack, e.g. Trumpet Winsock); where the socket library dials the modem to serve the first bind(2). Sort of like auto-mounting a network share to serve a VFS open(2).
Try it yourself: boot up a Windows 95 OSR2 machine with a (configured) modem, and try e.g. loading your Outlook Express email. The modem will dial. It's a feature of the socket stack.
These socket stacks would also automatically hang up the modem if the stack was idle (= no open sockets) for long enough.
My point was that a quiescent HTML4 browser has no open sockets, whether or not it's intentionally "offline." If you do as you say — load up a bunch of pages, and then sit there reading them — your modem will hang up, whether or not you play with Netscape's toggles.
(On single-tasking OSes like DOS — where a TCP/IP socket stack would be a part of a program, rather than a part of the OS — there was software that would eagerly hang up the modem whenever its internal socket refcount dropped to zero. But this isn't really a useful strategy for a multitasking OS, since a lot of things — e.g. AOL's chatroom software presaging AIM — would love to poll just often enough to cause the line that had just disconnected to reconnect. Since calls were charged per-minute rather than per-second, these reconnects had overhead costs!)
> [Netscape's] offline mode let you disable automatic dialing of the modem.
When you do... what?
When you first open the browser, to avoid loading your home page? (I guess that's sensible, especially if you're using Netscape in its capacity as an email client to read your already-synced email; or using it to author and test HTML; or using it to read local HTML documentation. And yet, not too sensible, since you need to open the browser to get to that toggle... is this a thing you had to think about in advance, like turning off your AC before shutting off your car?)
But I think you're implying that it's for when you try to navigate to a URL in the address bar, or click a link.
In which case, would the page, in fact, be served from the client-side cache, or would you just get nothing? (Was HTTP client-side caching even a thing in the early 90s? Did disks have the room to hold client-side caches? Did web servers by-and-large bother to send HTTP/1.0 Expires and Last-Modified headers? Etc.)
I used to go into offline-mode so the browser would access pages from the cache when I went to their URLs. It wasn’t a ton, but it was enough that you could queue up a handful of sites, go offline and then, if you accidentally closed the tab, re-open it and see the caches version.
Browser shows “I’m offline. Do you want to proceed?” dialog. If OK, tries to open socket. Upon such request, OS will try to dial up on modem with PPP, which takes ~30s. PPP session disconnects after few minutes. Else abort. If browser is online in the first place, skip that dialog part.
- Was caching a thing? Did disks have room to hold cache?
Oh it was, there were rooms. Alas, 56kbps(7kB/s) ideal means each pages are kilobytes to single megabyte large at most. ADSL connections at ~1Mbps(1/8 MB/s) means a 256kB page loads in 1 second on a fine day. Even a 200MB disk space holds 1024 of such ~200kB pages, and IE back in those days had a hidden attributes but ordinary folder deep down from C: that holds about that large random cache of files that it decided to hold.
> In which case, would the page, in fact, be served from the client-side cache, or would you just get nothing?
IIRC, some of the browsers, in "offline mode", would actually serve pages from the local cache, not even attempting to fetch them from the remote server. If you attempted to navigate to a page that hadn't been cached, you got an error of some kind.
> Was HTTP client-side caching even a thing in the early 90s? Did disks have the room to hold client-side caches?
I was considered mad at the time for upping my cache to a whopping 2Mb by friends, but Netscape's cache was highly configurable.
Things like cache pages, but not images, always cache bookmarked pages, cache iframe pages (which were often navigation), etc. Netscape 4 added CSS to that mix.
