Belts and brakes

[luddlump]

Set off to work this morning then heard noise under bonnet and battery light came on and T-belt warning light, as I was looking for see here safe to stop the brake warning light came on and needed to put huge pressure on brake pedal to stop car. I found one alternator belt had snapped and damaged two other belts, the other alternator belt and power steering one.
But why no brake pressure do one of these belts also drive the brake booster or servo/ vacuum system on brakes.
All 4 belts now off including aircon and new set to be fitted later.

[BUSHWHACKER]

There's a vacuum pump on the alternator.
If the alternator stops, the vacuum supply for the brakes won't build up.

[luddlump]

Thanks for that