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Apples detailed specification
The iMac "Core 2 Duo" 2.4 20-Inch Aluminum (Early 2008/Penryn) features a 2.4 GHz Intel "Core 2 Duo" processor (E8135), with two independent processor "cores" on a single silicon chip, a 6 MB shared level 2 cache, a 1066 MHz system bus, 4 GB of RAM (800 MHz DDR2 SDRAM, PC2-6400), a 250 GB (7200 RPM) Serial ATA hard drive, a vertically-mounted slot-loading DVD±R DL "SuperDrive", ATI Radeon HD 2400 XT graphics acceleration with 128 MB of GDDR3 memory, a built-in iSight video camera, and built-in stereo speakers underneath the 20" glossy TFT Active Matrix LCD (1680x1050 native) display.
Connectivity includes three USB 2.0 ports, a Firewire "400" port and a Firewire "800" port, built-in AirPort Extreme, and Gigabit Ethernet, as well as mini-DVI, which supports an external display in "extended desktop" mode.
Externally, the iMac "Core 2 Duo" Aluminum (Early 2008/Penryn) models essentially are the same as the original Aluminum models that these replaced, with the same housing and glass cover that "joins precisely to the aluminum enclosure creating a virtually seamless front surface". The Early 2008/Penryn models, likewise, are paired with the same "ultra-thin alumium" Apple Keyboard (0.33 inches at the front edge).
Internally, however, the "Early 2008/Penryn" revision of the "Aluminum Core 2 Duo" models have faster and more energy-efficient 45 nm "Penryn" processors -- compared to 65 nm "Merom" processors in the original "Aluminum" models -- larger level 2 caches (6 MB compared to 4 MB), faster frontside buses (1066 MHz compared to 800 MHz), and faster memory (PC2-6400 compared to PC2-5300).