Those ultra fast systems also have ultra fast I/O. Buffering is critical to get good performance e.g. on your NVMe. The difference between writing one character at a time and writing a few megabytes at a time would be many orders of magnitude (x1000? x10000?) enough to make pipe processing of large files be unacceptably slow. Even between processes you want to move large blocks of data otherwise you're just context switching all the time. You can try this by flushing after every character in a toy program and do some sort of chain `toy largefile | toy | toy > mycopy`