How to get Cache and Buffer size and RPM of a hard disk using WMI?

How to get Cache and Buffer size and RPM of a hard disk using WMI?

I can get the serial number and type of a hard disk using WMI with
Win32_PhysicalMedia and Win32_DiskDrive. But I am unable to get Hard Disk
cache/buffer size (usually it is 2 or 8 or 16 BM) and RPM (usually it is
5400 or 7200). Please tell me what is the Syntax to get these information
in WMI. Thanks. I am using Windows with VS2010 C++.