Total days who-is data will be stored lower value means more requests to external service providers, the default is 365 days, negative values are not supported.
This is not memory storage but serialized long term storage in days.
Most of this data is rather stable as it's not often that a ISP changes IP address scope
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