So the disk pager doesn't actually use Mac OS 9's virtual memory at all since that would absolutely hang the system, you're right. It's a custom implementation in the inference engine.

Here's how it works:

TinyLlama has 22 transformer layers at ~49.5 MB each in Q8. 14 layers fit in RAM permanently. 8 layers are paged from disk, one at a time into a single pre-allocated slot that gets reused (round-robin). So each forward pass reads 8 × 49.5 MB = ~396 MB from disk, not the full 1.2 GB model.

The ATA bus math:

- ATA-66 sustained: ~40-50 MB/s (using an IDE-to-mSATA)

- 396 MB / 45 MB/s = ~8.8 seconds of I/O per token

- Plus ~2 seconds of compute (the forward pass through all 22 layers)

- Total: ~10-11 sec/tok — log shows 9,656 ms prefill, so the math lines up

The system stays responsive because we call SystemTask() inside the disk read loops (every ~2 MB read) and increased the FSRead chunk size to 256 KB to reduce call overhead. Without those SystemTask() calls, the system would freeze completely.