Hard drives designed for the original models of Xbox 360 are not directly compatible with Xbox 360 S models and vice versa. However, if removed from its case, the 2.5" SATA hard drive within older model HDD units may be inserted into the Xbox 360 S hard drive slot and will function normally. On August 20, 2010, Microsoft announced a 250 GB stand-alone hard drive for use with Xbox 360 S models priced at US$129.99 The actual drives inside their respective casings are standard 2.5" (laptop-size) SATA hard disk drives loaded with special firmware. However, the Microsoft versions are notably more expensive than standard drives.