Mode            H period us V lines  Sync    
VGA TEXT        31.7777     449      -H+V I
EGA on VGA      31.7777     449      +H-V I
CGA on VGA      31.459      449      -H+V I
VGA Graphics    31.7777     525      -H-V N
Real EGA        45.764      365      +H-V I
Real CGA        63.695      262      +H+V N