[SH] Mike: The variables in the Memory Usage (usage => Usage) group can be set at runtime, while the others can only be set at startup. So what happens when you click Apply Changes? Only changes to my.ini/my.cnf, or also changes to runtime settings? (Probably not, as the section name is Startup variables; just want to make sure. This tab allows you to configure variables that affect the networking behavior, memory usage and directory locations of the MySQL server.
Networking
Use socket/named pipe file: If enabled, connections to the MySQL server from the local host will not use the TCP/IP protocol, but rather sockets (on Unix-like systems) or named pipes (on Windows NT family systems like Windows NT, Windows 2000, and Windows XP). This can make client-server communication significantly faster on some systems, but it will be slower in many Windows configurations (see the Selecting a Windows Server section for details).
Memory Usage [SH] Mike: usage => Usage
You can find more information on the variables that influence that memory usage in the SHOW VARIABLES section.
Max allowed packet: The maximum size of one packet sent from the client to the server, or the other way around. Note that this can be set to a maximum value of 16 kilobytes (k) for MySQL version 3.23[UB] I think we should not care about 3.* servers., and to 1 gigabyte (1000 M [SH] Paul: 1000, or 1024?)) as of MySQL version 4.0.
Table cache: The number of tables that the MySQL server can simultaneously keep open. You can find more information on this parameter in the How MySQL Opens and Closes Tables section.
Record buffer: [SH] Mike: record_buffer is the old name, which might be confusing to use here. read_buffer_size, so better call it "Read buffer". The size of this parameter influences performance when the MySQL server performs many sequential table scans.
Sort buffer: The size of this buffer influences the performance in sort operations, like in ORDER BY or GROUP BY clauses.
Directories [SH] Mike: I wonder what happens if you change Base or Data directory without moving the files. Are these things that we actually want people to be able to set in MySQL Administrator?
You can find information about the MySQL directories in the Installation Layouts section.
Base directory: The MySQL installation directory.
Data directory: The location where MySQL stores databases and tables. Note that there may be other locations where some databases and tables get stored; this may be the case for InnoDB tables if the InnoDB tablespace is located in places other than the data directory.
Temp directory: The location MySQL uses to store temporary files.