[Someone]

Mac OS similarly, over time, grew various short Pascal string types to be used in its APIs. https://opensource.apple.com/source/CarbonHeaders/CarbonHead...:

    typedef unsigned char Str255[256];
    typedef unsigned char Str63[64];
    typedef unsigned char Str32[33];
    typedef unsigned char Str31[32];
    typedef unsigned char Str27[28];
    typedef unsigned char Str15[16];

The 2^n-1 sizes are cache-line don’t need explanation, I think. 27 was the maximum length of a volume name in MFS, the original Macintosh file system (which was a strange mix of backwards (no directories) and forwards (255 character file names) thinking).

Str32 was used in AppleTalk (and probably a design error or bug; Str31 is a more ‘natural’ type)