In order to process more data than can fit in memory, programs can spill some of that data to a slower but larger storage, such as NVMe drives. Through a combination of two rather obscure .NET features (memory-mapped files and memory managers), this can be done from C# with little to no performance overhead. This talk given at Warsaw IT Days 2023 dives into the deep details how this works, and discusses how the open source NuGet package Lokad.ScratchSpace hides most of those details from developers.