The MacBook Air was the first compact laptop sold by Apple since the full-featured 12" PowerBook G4 was stopped in 2006. It was also Apple's first computer with an optional solid-state storage drive. ArsTechnica found "moderate" performance improvements of the 64 GB solid-state drive of the first generation Air over the standard 80 GB hard drive in tests. On October 14, 2008, new models were announced boasting improved capacities of 128 GB (solid-state) and 120 GB (hard drive). The Air comes standard with 2 GB non-upgradable RAM. The CPU on the original Air was an Intel Core 2 Duo chip especially designed to be 40 percent the size of the standard Core 2 Duo chip. The current model has a low voltage, small form factor Core 2 Duo "Penryn" with 6 MB of cache, running on a 1066 MHz bus. MacBook Air has no user-replaceable parts. The hard drive, memory, and battery are enclosed within the casing, with memory soldered directly to the logicboard. MacBook Air's battery is enclosed within the case but can be replaced using normal screwdrivers, though it is unclear whether this process would void the notebook's warranty. As part of the out-of-warranty service, Apple offers to replace the battery for a fee.