The XFR
The XFR (Extended Frequency Range) is essentially an extension or enhancement to the standard CPB (Turbo) algorithm. In scenarios where all of the various limiters (power, current and thermal) have margins, the CPU is allowed to boost above its nominal base and boost speeds. Just like the standard CPB algorithm, the XFR has separate clock ceilings for a single core and all core operation.
For example, for the 1800X SKU the clock configuration is following: 3.6GHz all core frequency (MACF), 4.0GHz single core frequency (MSCF), 3.7GHz maximum all core XFR ceiling (ACXFRC) and 4.1GHz maximum single core XFR ceiling (SCXFRC).
The number of XFR bins (n x 100MHz) might vary between the different SKUs, however for the 1800X model there is a single XFR bin available for both all core and single core operations. In typical consumer workloads, the CPU will generally be able to reside in the XFR states (3.7GHz / 4.1GHz) constantly, however in certain specialized workloads (such as Linpack or Prime95) the frequency usually decreases towards the base frequencies (3.6GHz / 4.0GHz).
Ryzen: Strictly technical