Private Server

Private Servers are Servers that are not maintained or sanctioned by Square Enix but rather by third parties. Due to the legality of those servers being gray area, this article will only explain the concept but will not mention or link to any specific server.
== Background ==
As with all MMO games, the game software purchased and downloaded by players is the game client. When launched, it connects to a game server and communicates all player actions to it. The server links between players, informing the game client of other players' activities. The game server also controls the behavior of mobs and NPCs.
=== Method ===
Unlike the game client, which is available for download to anyone who has purchased the game, the server software runs on Square Enix' servers and never released to the public for download.
An MMO server emulator is third party software that mimics the behavior of the official server software, allowing the game client to connect to it and play just like on an official server. Since Square Enix has not made the official server software available (nor has it ever leaked out), server emulators for FFXI were made by reverse engineering the game binary, as well as the network traffic between the game client and the official servers, with the aim of documenting the network protocol and re-implementing the server side.
When a 3rd party installs and runs such software on their own servers and makes them available to others, it is called a Private Server.
== Aims ==
There are several aims for creating FFXI private servers:
* Preservation - While Square Enix has made a statement that it has no plans of shutting down the official servers in the foreseeable future, the possibility of that happening at some point is not something easily discarded. The existence of private servers mean that even should Square Enix ever sunset the game officially, as long as someone is willing to run a private server, FFXI will live on (as has happened with various other MMOs).
* Customization - Hardly any of the private servers aim to be exact copies of the official service. Virtually all private servers offer a different game experience than the official service and from each other (see the "types" section below).
* Availability - Running the server emulator software on your own computer allows you to play with friends on a LAN, in an air-gapped network or even by yourself completely offline (the latter is not recommended, Vana'diel is a very sad place when you're alone).
== Issues ==
Private servers also have various issues coming with them:
* Legality - This is a gray area. While the server emulator software has been written entirely from scratch by the community and therefore does not contain any intellectual property owned by Square Enix, the fact is that it can be used to allow playing FFXI without a proper paid subscription. This is not unlike game console emulators, which are generally considered legal but have been challenged by manufacturers and studios in the past with various results.
* Inaccuracies - Since the official server software has never been made public, developers of server emulator software (and by proxy, private servers), don't have access to the exact algorithms controlling certain aspects, and have to rely on whatever public information is available and their own experience. In some cases, those extrapolations prove to be incorrect or plain wrong. For example, in 2020, during a developer Q&A session, Square Enix developers have revealed how the Treasure Hunter trait works internally in the official servers, which proved to be very different than how private servers (previously) implemented it.
* Bugs - The server emulator software is developed by hobbyists and private servers are maintained by hobbyists as well. Since it is no one's day job, bugs are found frequently, and fixes rely on whatever free time the developers and maintainers have. Private servers are never subject to any SLA (service level agreement).
* Transfer - There is no equivalent of the World Transfer Service. Characters cannot be transferred between official Square Enix servers and private servers, nor between different private servers. To play on a private servers, a new character needs to be created and the game begins from scratch.
== Types ==
As mentioned before, hardly any private servers offer the same experience as the official service. There are two main types of private servers:
=== Past Era Servers ===
These private servers aim to recreate the game experience as it was at a certain time point in the past. The point in time that the server aims to recreate is called its "era", and the exact time point being the "cutoff date". Generally, all content which was in the official service at the cutoff date will be included in the private server (or at least planned to be included) and all content which came after that date not being included, although some servers offer certain "quality of life" improvements from later eras (e.g., Mog Wardrobes). On the other hand, any "game changing" features are hardly ever included. For instance, no era type server would offer trust magic - they aim to create the past hardcore experience, which usually forced players to team up frequently to make progress.
The most common eras for this type of private servers are the end of Chains of Promathia, the end of Treasures of Aht Urhgan or the middle of Wings of the Goddess. Almost all era type private servers are capped to level 75.
Content that was introduced to FFXI after the cutoff date and therefore not included in a private server is referred to as "Out of Era" content and often abbreviated "OOE".
=== Custom Servers ===
These servers offer an experience different than the official experience, starting from small changes like fine-tuning monsters' strength and items' drop rates, through introducing custom quests, all the way to game changing features such as having two main jobs.