I have an DH77EB that is no longer supported by intel
No chat, email / online support.
I have 2x8GiB DIMM DDR3 Synchronous 1333 MHz
I wish to expand it to 32GB
1. IYO should I invest in 2 extra units (2x8GB) with speed adequate to this board?
As the specs say: Support for DDR3 1600 MHz, DDR3 1333 MHz, and DDR3 1066 MHz DIMMs
That means Up to 1600 MHz...
2. Will the board function if my existing DIMMs are 1333 MHz??
So the board will be running 2x8GiB DIMM DDR3 1333 MHz & 2x8GiB DIMM DDR3 1600 MHz
Likely, if you add two 1600 DIMMs, they will operate at 1333 because of the speed of the other DIMMs present. Currently (I will presume), you have your two DIMMs in separate channels. When you add the new DIMMs, you want to move the two existing DIMMs to one channel and put the new DIMMs in the other channel.
As always, my recommendation is to find a way to test with extra DIMMs installed before you actually purchase any...
Hope this helps,
Please bear in mind that the memory controller hub is part of the processor now, so, memory speed will also depend on the processor model.
You can check supported memory speed at ark.intel.com, you need to select your processor model.