/architecture and /tune are actually carry-overs from CVF. /architecture does the same thing as /Qx - specifies which "level" of instruction set architecture to require for the program.
This article explains the various /Qx options. If you run a program compiled with a /Qx option on a processor that does not support that option, it will fail. /Qax enables automatic CPU dispatch where it looks to see what processor type you're running on and selects one of up to three alternate code paths depending on the type. You can use /Qx and /Qax together to specify a "least common denominator".
/tune adjusts the choices the compiler makes when generating code to favor one level of processor over another without affecting which instruction set to use.
In a future release, we're going to simplify these options and make them easier to understand. No more cryptic letter codes.
