vim defaults to 100% backwards compatible with vi. It has an option "nocompat" that enables some non-backwards compatible improvements.

ZZ definitely still works regardless of nocompat though.

ZZ and ZQ work, at least on every instance of vim I've ever used

vi is built-in in arch installation. so...

Vi is everywhere. Its part of the POSIX standard and comes out of the box (in one flavor or another) with every Linux Distro, OSX, HP-UX, AIX, Solaris, Darwin, FreeBSD, OpenBSD, and DragonFlyBSD.

ViM is just Vi iMproved. They share most their keybinds but VIM has the whole plugin architecture thing.

This is a big sticking point for a lot of VIM users [1]. If you ever end up on a Unix box that doesn't have VIM, you can always fall back on Vi.

[1]: /users/religious fanatics/

At least on Ubuntu, vi is really VIM:

    zck@zck-desktop:~$ vi --version
    VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Jan  2 2014 19:39:32)

On Arch, vi is the original Bill Joy vi.

    $ vi --version
    vi: illegal option -- -
    Usage: vi [- | -s] [-l] [-L] [-R] [-r [file]] [-t tag]
           [-v] [-V] [-w size] [+cmd | -c cmd] file...
    $ pacman -Qi vi
    Name           : vi
    Version        : 1:070224-2
    Description    : The original ex/vi text editor
    Architecture   : x86_64
    URL            : http://ex-vi.sourceforge.net/
    Licenses       : custom:ex
    Groups         : base
    Provides       : None
    Depends On     : ncurses
    Optional Deps  : s-nail: used by the preserve command for notification [installed]
    Required By    : None
    Optional For   : None
    Conflicts With : None
    Replaces       : None
    Installed Size : 290.00 KiB
    Packager       : Evangelos Foutras <[email protected]>
    Build Date     : Sun 06 Sep 2015 03:34:15 PM EDT
    Install Date   : Fri 18 Sep 2015 10:33:33 PM EDT
    Install Reason : Explicitly installed
    Install Script : No
    Validated By   : Signature

(ok, I'm not actually on Arch, but I'm downstream of Arch, and that package is directly from Arch)

You are correct:

https://www.archlinux.org/packages/core/x86_64/vi/

Eh, yeah, but it usually links to the "basic" version (which, I assume, is compatibility mode for old school vi).

    root@dicks:~# which vi
    /usr/bin/vi
    root@dicks:~# file /usr/bin/vi
    /usr/bin/vi: symbolic link to `/etc/alternatives/vi'
    root@dicks:~# file /etc/alternatives/vi
    /etc/alternatives/vi: symbolic link to    `/usr/bin/vim.basic'
    root@dicks:~# file /usr/bin/vim.basic
    /usr/bin/vim.basic: ELF 64-bit LSB  executable, x86-64, (snip)
    root@dicks:~# vi --version
    VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Jan  2 2014 19:39:32)