This IDC Insight provides an initial forecast for attach rates through 2010 for two competing nonvolatile PC hardware caching technologies: hybrid hard disk drives (H-HDDs) and alternative embedded NAND solutions in the PC. Underlying assumptions and dynamics impacting IDC's forecast are outlined, including the potential incursion of flash-based solid state disks (SSDs) as a mass storage device in PCs in the latter portion of the forecast period.