https://en.wikipedia.org/wiki/VESA_BIOS_Extensions#Linux_video_mode_numbers

The Linux kernel allows the user to select the VESA mode at boot time by 
passing a code in memory to the kernel. The LILO boot loader passes this 
code based on a "vga" parameter in its configuration file. It takes the form 
'vga=XXX', where XXX is the decimal value, or 'vga=0xHHH', where HHH is the 
hexadecimal value. However, the 'vga=' boot loader parameter does not directly 
accept VESA video mode numbers; rather, the Linux video mode number is the VESA 
number plus 512 (in the case of the decimal representation) or plus 0x200 (in 
the case of the hexadecimal representation). For example, the defined VESA 
value of 257 (0x101), representing 640x480 and 256 colours, has an equivalent 
Linux video mode value of 769 (0x301).

vga=774   1280 x 1024  ( 16 colours)
vga=772   1024 x  768  ( 16 colours)
vga=770    800 x  600  ( 16 colours)
vga=796   1600 x 1200  (256 colours)