AR pistol gas system help

[barbasol]

1. Do all 9mm ar pistol uppers operate on a blowback design or are there uppers that use gas blocks and tubes like the ar platform?

2. If there are both what ar the pros and cons of each?

Thanks

[Quiet]

1. All 9x19mm AR uppers are blowback.
2. 9x19mm blowback is more reliable than gas-operated 9x19mm.