990DT board is microATX but still in ATX family.  It is just smaller in width than ATX.  You still cannot install it in a BTX case. [IMAGE]  
Hello, I have a Intel i7-2600 and I want to put an Optiplex 990 DT motherboard onto an Optiplex 760 case. The front panel connectors are similar and I am going to dremel the back IO shield. Bonus question, does the i7-2600, this package of ram: Gigastone DDR3 16GB (8GBx2) 1600MHz PC3-12800 CL11 1.5V UDIMM 240 Pin Unbuffered Non ECC for PC Computer Desktop Memory Module Ram Upgrade Kit at Amazon.com, and this CPU fan: Amazon.com: Antec CPU Cooler, Blue LED Fan 92mm, for Intel LGA 775/1150/1151/1155/1156 & AMD Socket FM1/AM3/AM3+/AM2+/AM2/AM4, A30: Industrial & Scientific work with the case and mobo? (for case fan I am going to use this:Amazon.com: Pocaton 5Pin Female to 4Pin Male Socket Connector Jack PWM Cooling Fan Power Cable Compatible with DELL PC: Computers & Accessories).
Can you put an Optiplex 990 DT motherboard into a Optiplex 760 MT case?