Microsoft

"You are architecting the memory subsystem for a custom neural processing unit (NPU) handling mixed-precision matrix multiplication (FP8/INT4) for 100B+ parameter models": The interviewer asked how to sustain 95%+ compute-core utilization when tensor weights exceed on-chip SRAM capacity and off-chip HBM3 bandwidth is heavily saturated; I detailed a memory orchestration engine utilizing hardware-level double-buffered scratchpad SRAM banks, asynchronous DMA double-pumping driven by compile-time address stride generators, and micro-tiled weight layout transformation to maximize spatial data reuse across 2D systolic multiply-accumulate (MAC) arrays without dynamic indexing overhead. "A mission-critical fly-by-wire flight control system requires deterministic consensus across triple-modular redundant (TMR) flight computers under Byzantine fault conditions": The panel challenged me to achieve synchronized actuator voting within an 8-millisecond control loop despite transient bit-flips, sensor noise, and asymmetric communication link failures; I walked through implementing the Byzantine Agreement protocol (Pease-Shostak-Lamport variant) constrained to 3m+1 nodes, replacing exact value agreement with a bounded inexact consensus convergence algorithm, where bounded floating-point sensor deviations are continuously filtered using a fault-tolerant midpoint algorithm to prevent single-channel divergence. "Design the unified virtual memory (UVM) migration engine inside a multi-GPU runtime connecting 8 GPUs over an asymmetric NVLink mesh": The interviewer asked how to prevent memory thrashing and false-sharing page migration loops when multiple execution streams concurrently touch disjoint byte offsets within the same 2MB huge page; I formulated an adaptive page-fault handler utilizing hardware hardware access-counter telemetry, dynamic sub-page splitting (splitting 2MB contiguous mappings into 4KB pages under multi-GPU write contention), and a cost-benefit migration model that dynamically transitions between remote NVLink direct peer-to-peer memory access and physical page migration based on locality reuse thresholds.