alt Hacker NewsAOL was your ISP - you would connect via your telephone line instead of cable/fiber. Your modem would call their number and establish a connection. No one else could use the phone while you were online.
When you connected, it would load the AOL application which contained most of what AOL offered - built in AIM (AOL instant messaging), a web browser, group chats, keyword search, email, etc.
You were still connected to the internet and could use alternate browsers, but most people stayed inside the AOL app and ecosystem. Keywords were a time before search, where companies could buy keywords (from AOL) and then when people searched them they would show up. It was kinda a separate system from DNS that AOL tried to profit from.
You had competitors like Prodigy and CompuServe offering similar dial-up + custom app offers.
You wouldn't use the AOL app without having AOL dial-up service (although I recall them offering it separately late in its life, bring your own internet). People thought "AOL" was the internet. You might recall the classic "You've got mail" movie. That was from the AOL app which loaded after connecting.
aside: It's crazy how AOL could have become Facebook. AIM chat was the main focus - but AIM had "profiles" which you could customize, and I did - even with daily status updates. Modern Facebook is basically the reverse - profiles with a chat attached.
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Did the AOL protocol (whatever the AOL app itself used for chat etc.) go over TCP/IP, or was that its own network, parallel to the internet?
Was the limitation that you couldn't use AOL from a different ISP artificial (whitelisted IP ranges, no routing to relevant addresses from the outside), or did it actually use an "internetless" protocol that you just couldn't emulate if all you had was the internet?
I vaguely remember reading somewhere that internet access was a late addition to AOL, hence the question.
I was pretty young at the time, but I think it started as basically a BBS. With an Internet backbone so a bunch of local numbers could all access the same server. They added Internet access later, and initially only via their own browser.
AOL was an "online service", internet connectivity was provided starting in the mid-90s but the real value was in their proprietary members-only services. An online service was more or less a large BBS you dialed into via modem, the first of which could be accessed with an ordinary telecoms program but later ones like AOL and Prodigy required special client software that could decode the proprietary protocol allowing the service to send graphics, menus, and other information to present a UI to the user.
AOL started off as something different from an ISP.
Like Prodigy and Compuserve and GEnie and some others, it was an on-line information system. Chat, message boards, news, stock quotes, (limited) shopping, games, software downloads, etc. But all within a single system. Kind of like a nationwide/global BBS, but with a GUI interface. In the 80s, all these systems were independent, in the early 90s they got internet email, and the mid 90s added web browsers and (eventually) real tcp/ip.