I needed to write a quick program to extract some data from a binary file today, so I reached for Borland Pascal 7. The actual program took a couple of minutes to get right… most of it because of a 'feature': if you open a file in binary (as opposed to text) mode, you have to say how many bytes you will read at a time.
If you forget – as I do every so often – it defaults to… 128 bytes.
Why 128 bytes rather than one?
Because that was the size of a sector on the original 8" floppy disk, which had 77 tracks of 26 sectors back in the early 1970s. Early versions of CP/M could only read and write in 128 byte chunks, and Turbo Pascal was originally released for CP/M, so that was the sensible value for the default.