Non-volatile resistive switching (NVRS) has been recently observed with synthesized monolayer molybdenum disulfide (MoS2) as the active layer and termed atomristors [1]. In this paper, we demonstrate the fastest switching speed (<15 ns) among all crystalline two-dimensional (2D) related NVRS devices to the best of our knowledge. For the first time, ab-initio simulation results of atomristors elucidate the mechanism revealing favorable substitution of specific metal ions into sulfur vacancies during switching. This insight combined with area-scaling experimental studies indicate a local conductive-bridge-like nature. The proposed mechanism is further supported by sulfur annealing recovery phenomenon. Moreover, exfoliated MoS2 monolayer is demonstrated to have memory effect for the first time, expanding the materials beyond synthesized films. State-of-the-art non-volatile RF switches based on MoS2 atomristors were prepared, featuring 0.25 dB insertion loss, 29 dB isolation (both at 67 GHz), and 70 THz cutoff frequency, a record performance compared to emerging RF switches. Our pioneering work suggests that memory effect maybe present in dozens or 100s of 2D monolayers similar to MoS2 paving the path for new scientific studies for understanding the rich physics, and engineering research towards diverse device applications.