The "un" variant of kernel packages is a low latency desktop oriented 2.6.x kernel which should support wide range of hardware, but it is not 'official' ALT Linux kernel and you can use it for you own risk. В un-def, кстати, то же самое. А уже в t6/p6 std-def и un-def версии 3.x.
Да и low latency, возможно, от ll-smp.