Este é o / p do dmesg com uma placa de vídeo 1G discreta ATI 6370HD. "RAM VRAM detectada = 1024M, BAR = 256M", verifique esta linha.
sourajit@sourajit:~$ sudo dmesg | grep drm
[ 6.126816] [drm] Initialized drm 1.1.0 20060810
[ 6.541907] [drm] radeon defaulting to kernel modesetting.
[ 6.541910] [drm] radeon kernel modesetting enabled.
[ 6.542102] [drm] initializing kernel modesetting (CEDAR 0x1002:0x68E4 0x17AA:0x397A).
[ 6.542142] [drm] register mmio base: 0xE0600000
[ 6.542143] [drm] register mmio size: 131072
[ 7.406572] [drm] Detected VRAM RAM=1024M, BAR=256M
[ 7.406576] [drm] RAM width 64bits DDR
[ 7.406654] [drm] radeon: 1024M of VRAM memory ready
[ 7.406655] [drm] radeon: 512M of GTT memory ready.