Higan is slow precisely because it's cycle-accurate Low Level Emulation. This requires emulating the machine at every cycle tick and replicating every portion o

Higan is slow precisely because it's cycle-accurate Low Level Emulation. This requires emulating the machine at every cycle tick and replicating every portion of the machine from each step up. Modern machine emulators (outside of hypervisor based virtualization) don't use cycle-accurate emulation. Instead they use high level techniques such as intercepting 3d draw routines and translating them into OpenGL/DirectX/Vulkan API calls. In addition, they take heavy advantage of JIT to compile the code to more close to baremetal instructions for the target architecture, which isn't viable for cycle accuracy. One of the main reasons older machines require LLE is that they're cycle intolerant and rely on specific timing for many effects (although, you can still get 90% there with most, just being "close enough"). Newer machines (from the PSX on, for the most part) use pipelined architectures and are strongly interrupt based, so timing is generally less important. Tl;Dr - No matter the case, cycle-accurate is the ideal case. But newer machines are just more tolerant to bad timing than older machines.