It can be your harddrive that's to slow.
In Nero try a burn where you Testburn and Determine maximum speed.
In "File/Preferences/Cache/Test all drivespeed" you can check your Harddrive performance.
According LiteOn the specifications:
System Requirement :
CPU Pentium 166MHz or faster, 128MB DRAM required
HDD must have access time < 20ms, with a minimum of 100MB Free space.
If you can burn at 20x without Smartburn kicking in, you have dma enabled.