The Thermaltake Mozart Sx Slim HTPC case uses some innovative ideas to let you fit a full ATX board, and even a normal 1 slot PCIe video card in a tiny area.  hardCOREware has posted a full review of this well made HTPC case.
“Designing a full ATX HTPC case must be very complicated; it’s not like you can simply take a tower case and flip it down to its side! An HTPC case must be slim, quiet, and aesthetic.

Making a low-profile case is even trickier. You have to deal with installing peripherals horizontally, and trying to squeeze in as many components as you can, including the power supply.

Thermaltake has taken a shot at designing an HTPC case that is just 90mm tall, yet supports a full ATX motherboard and power supply. Does it succeed where so many others have failed?”

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