Infos about US Army Specialist and Warrant Officer Ranks

[DiavoloRosso]

I have a few questions about the Specialist & Warrant Officers ranks.

I have understood that they have a "non command" role, but still I
havent figured out which is their role. To make things more complex are
the "ghost" SP8 & SP9, which was their supposed role?

Regarding the Warrant Officers, with the introduction of the new CWO
W-5 badge, wha happened to the Master Warrant Officers W-4, they kept
wearing their badges till promoted to the CWO W-5 or else? And how long
takes a Warrant officer to reach for the W-4 or W-5 paygrade?

Thanx.

Cheers from Italy

E*