The base value is used with the raw value for certain counter types. For example, if you want to determine the percentage utilization, you need to know both how much capacity was used and how much was available. The base represents how much was available and the raw value how much was used in that scenario.
Requirements
Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2