This does not work and is not supported.

XEON 1230 is 80W cpu which is also not supported with proprietary stock 290W power supply.

Intel® Server Board S1200V3RPS  is required for this processor.

https://ark.intel.com/content/www/us/en/ark/products/71385/intel-server-board-s1200v3rps.html

how to enable hyperthreading in bios ?

i cant find such option in my 9020MT

That's Nonsense.

E3 1231 is an 80W CPU that is 22 NM and does not have INTEL HD Graphics.

https://ark.intel.com/content/www/us/en/ark/products/80910/intel-xeon-processor-e3-1231-v3-8m-cache-3-40-ghz.html

While not "officially" supported, there are quite a few Optiplex 9020 systems running Xeons on userbenchmark.com.

To see if someone's running a specific CPU/SSD/HD/graphics card, etc. in your system:

1. Go to userbenchmark.com and search for your system from search area in upper-right corner. 
2. Once your specific system is selected scroll down and click on "Best Build (Edit with custom PC builder)". 
3. On left-hand side remove with gray "X" all of CPU, GPU, SSD and RAM - leaving only MBD (the motherboard/system model). 
4. Then click desired tab ("CPU" in this case) and "Change Baseline CPU". 
5. To see how many benchmarks have this criteria, click "Load baseline user benchmarks" in lower-left section of page.  (If that button is not present, there are no benchmarks with your criteria.) 
6. From the list of benchmarks, you can click and drill down to system specifics.

Using the above on the Optiplex 9020 (which has 10,034 benchmarks), for the Xeons mentioned in this thread (so far) I see:

Xeon E3-1230 V3 - one hit

Xeon E3-1231 V3 - one hit

Above and Nicolai.Frost in this thread claiming it works, debunks the false idea that Xeon's don't work in the Optiplex 9020.  For some of the Xeon's you'll need a discrete graphics card, since some don't have integrated graphics.

I would probably opt for one of the Xeon's with integrated graphics, like the E3-1246 V3, which has HD Graphics P4600.

Xeon E3-1246 V3 - hit #1, hit #2

For a list of E3-12xx V3 series CPUs and which ones have integrated graphics (GPU), see here.

Let's cut the nonsense. Speedstep says a Xeon will not work and is taking into account factors such as O/B video and the power supply wattage but lets assume that you're running a 600W power supply and bypassing O/B video with a Graphics Card (because since when has O/B video/graphics ever been dependable? Maybe in the 70s when screens were green, orange, and white. I too run a "somewhat modded" 3020MT and want to push the limits and maximize my CPU however I see no point in going to a i7-4770/4790 just for a few more MHz.

Keep us posted on what works. Assuming does nothing.

Unless Speedstep is speaking from DIRECT PHYSICAL EXPERIENCE, I ignore what he says, because he's nearly always wrong.  He quotes from the Dell specs and manuals like they're gospel, when they are clearly NOT.

I picked up a 9020 MT from a college auction months ago that was running an E3-1225 v3 just fine. I installed Windows 10 on it without issues.

I "love" it when someone posts that they're running a configuration, and he has the gall to tell them that they can't be, simply because Dell docs say so.

3020 with xeon e3-1245v3 on user benchmark also... I'm going to be updating my bios to most recent and switching out i3 to a xeon e3- 1240v3 as I see it's much better than just going up to an i5 4690 and I found a xeon cpu locally for $50. No O/B video it's also 84watts rated same as i5/i7

I will be updating my experience with this and if it works out I'll be on user benchmark posting along the other 2 xeon 3020 mini towers.

I've been combing through the web for weeks and going crazy to get my parts together for my sleeper gaming optiplex. 

Xeon e3 1240 v3 specs... I was incorrect on 84watt tsp before in post it says here 80. Should I be alright if it is lesser tsp than 84 of i7 4790?

• # of Cores 4
• # of Threads 8
• Processor Base Frequency3.40 GHz
• Max Turbo Frequency3.80 GHz
• Cache 8 MB Intel® Smart Cache
• Intel® Turbo Boost Technology 2.0 Frequency‡3.80 GHz
• TDP 80 W

As u see here why I'm going for xeon over i7 as I'm teaming it up with 16gb 1600mhz Ddr3 and a nvidia 1030 or maybe 1080 gpu

Just to add a concrete data point to this conversation, I tried powering up an Optiplex 9020 MT with a Xeon E3-1246 V3, using the standard 290W power supply, and it does not work.  The diagnostic LED blinks in a 2,2 pattern.  The system starts up without issues using an i5-4690.

I've ordered the 365W power supply, and I'll post a follow-up (if I remember) to report whether or not it allows the system to boot with the Xeon.

Using the 365W power supply did not allow the 9020 MT to boot using the Xeon E3-1246 V3. The diagnostic LED is now blinking in a 2,3 pattern ("system board, memory or CPU failure").

I'm becoming increasingly skeptical that the 9020 can support a Xeon.  My next experiment will probably be to swap the 9020 motherboard for a Precision T1700 motherboard, where I think the Xeons are explicitly supported.

Ok, one final follow up. I replaced the Optiplex 9020 motherboard with a Precision T1700 motherboard, and it boots up just fine with the Xeon E3-1246 V3. I'm using the integrated graphics, not an external GPU (the 1246 is one of the Haswell Xeon CPUs that has integrated graphics.) Both the 290W and 365W PSUs work fine.

So, I conclude that the Optiplex 9020 doesn't support Xeon CPUs, but swapping the motherboard for a Precision T1700 motherboard (easily done since all of the connectors are the same) does allow Xeons to work.

Another follow-up: I was just able to successfully boot an Optiplex 9020 MT (BIOS rev A18) with a Xeon E3-1226 V3.  So, it does appear that it is possible to use Xeon CPUs with an Optiplex 9020 motherboards, at least in some specific combinations.

As I mentioned in another post, a Xeon 1220 V3 E3 works fine in a 7020 MT with an add on graphics card.