43 and 50 lines were not high resolution modes, they were just short-character modes. They still use native VGA 720x400 resolution. There were tools to program

43 and 50 lines were not high resolution modes, they were just short-character modes. They still use native VGA 720x400 resolution. There were tools to program VGA card to higher resolution text mode (svgatextmode), and also s3fb supports higher resolution text mode in kernel.