“Disk I/O may have been slow 10 or 20 years ago, but in 2022, reading a file sequentially from disk is very fast.”
A laptop NVMe drive reads 1.7 GB/s cold and 10.8 GB/s from cache. In his word count benchmark, reading the file was 14 percent of the runtime. The rest was the program. “It’s I/O bound” has been the excuse for slow code since spinning disks. Profile it. The slow part is usually you.