Out of the box at stock settings, this card gets about 260h/s on a single thread (more on that later in the post).

Of course, I had to mod the bios and tweak the XMR-STAK > amd.txt file settings. I also disabled the CPU mining, it's pointless on this unit. I'm getting between 430h/s ~ 440h/s steady, per card, using XMR-STAK.exe for 64bit Windows 10. About 30~34 watts power draw.. actually not bad for the cost / hashrate. I've had it running for a full day (well almost, like 18 hrs I think).

This is the card I picked up: Sapphire PULSE Radeon RX 550 2GB. http://pulse.sapphiretech.com/en/550-2.html

Microcenter is selling them for $89, and I got a flier in the mail for $10 off anything, so I decided to use it.
http://www.microcenter.com/search/search_results.aspx?Ntt=rx+550

WARNING
If you're new to mining, or aren't really too techie, be warned, you can basically brick your GPU if you do it incorrectly. Basically, if you screw up, you just bought a $90 brick.

The Rig (Haha, just an old low profile PC, GPU doesn't even fit)

• OS: Windows 10 Pro 64 Bit
• CPU: Old core 2 duo 2.2Ghz
• Motherboard: Old Acer thing didn't look for more info, it's old
• HDD: POS 500GB, 7200 RPM optical drive. Unless you're going to run the actual blockchain data on your machine, SSD vs HDD really makes no noticeable difference -- on clean installs -- this is not true if you're using your regular PC for mining, well because you have other crap running on the system.
• PSU: 450w
• GPU: Sapphire PULSE Radeon RX 550 2GB

What is needed

• Radeon Blockchain driver
  This is the official driver specifically for blockchain computing released by AMD.
  http://support.amd.com/en-us/kb-articles/Pages/Radeon-Software-Crimson-ReLive-Edition-Beta-for-Blockchain-Compute-Release-Notes.aspx
• AMD/ATI ATIFlash
  This is the what you'll need to flash the back up your original bios, and flash the new bios.
  https://www.techpowerup.com/download/ati-atiflash/
• Polaris Bios Editor
  This is what you will be using to modify the clock settings in the GPU.... just click on "One click setup", it's optimal for this card.
  https://github.com/jaschaknack/PolarisBiosEditor
• AMD/ATI Pixel Clock Patcher
  This is needed when you've completed flashing your bios, because if you don't, your PC will not recognize your graphic card after reboot.
  https://www.monitortests.com/forum/Thread-AMD-ATI-Pixel-Clock-Patcher
• MSI Afterburner
  This is just what I use to monitor the GPU
  https://www.msi.com/page/afterburner
• XMR-STAK for Windows 10 64bit
  This is what we'll be using to mine.
  https://github.com/fireice-uk/xmr-stak

How it's done

You'll notice by now that the CPU really doesn't matter, which is why many tutorials out there for building multi GPU rigs will just tell you to buy the cheapest Celeron CPU. There really is no benefit to CPU mining anymore, unless you like getting payouts every few months (if you're lucky). What's important in multi GPU building is that the board supports multi GPUs. That's basically it. (In the TL;DR nutshell).

1. This PC has a refreshed install of Windows 10 64bit. (I do this with everything I test, regardless of OS, I always do a fresh install. This ensures that there isn't anything running in the background that I don't want.)
2. Disabled the indexing on the main drive.
   https://www.online-tech-tips.com/computer-tips/simple-ways-to-increase-your-computers-performace-turn-off-indexing-on-your-local-drives/
3. Disabled Windows Update
   http://www.thewindowsclub.com/turn-off-windows-update-in-windows-10
4. OPTIONAL
   I enabled Remote Desktop, so I don't have to have a monitor and keyboard attached to this test unit after setup. I can just RDC into the unit from my main computer that I do work with. Remote Desktop is already built into Windows, so you don't need to install anything. If you have an android phone, Microsoft even has a Remote Desktop app for it. No clue about iOS.. I personally don't use anything iOS, only when a job requires me to build for it.
5. DO NOT INSTALL THE DRIVERS FROM AMD THAT CAME WITH THE GPU.
   Instead install the blockchain drivers posted earlier. Because you would need to uninstall the original drivers before installing them anyway. So don't bother installing them. You'll still be able to see your unit because Microsoft always has default low res drivers for any GPU. The installer will tell you to restart your machine. Do it.
6. Now install AMD/ATI ATIflash. Run it, it will show you your current bios. Save it, name it "Original-rx550-bios.rom" or something you can remember. Close the program.
7. Make a copy of the bios you just saved, and call it "Mod-rx550-bios.rom" or something you can remember.
8. Now install and run Polaris Bios Editor. Open the "Mod-rx550-bios.rom". Then at the bottom right, just click the one step timings. After spending about an hour tweaking the settings manually, the one click ones are the best for performance, stability, hashrate and power draw. In my opinion it is anyway. You can clock this baby up to almost 550h/s, but you're increasing your GPU wattage to about 60.. so double the power usage while only getting roughly 100h/s more.... not worth it once you figure in electricity costs. Now save the bios. You can just overwrite the "Mod-rx550-bios.rom" file. Close the program.
9. Now run AMD/ATI ATIflash again. This time load the modded "Mod-rx550-bios.rom" file. Then run the patch. This can take a minute or two. Don't worry if it looks like it "froze", it's not, its just thinking and patching and stuff. Once that's done, close the program.
10. Run AMD/ATI Pixel Clock Patcher. It'll just show you that it's detected your GPU. Run the patch.
11. Reboot your system.

XMR-STAK and its settings

If you're running XMR-STAK for the first time, it's going to ask you a few questions. (At this point, if you've never mined before, you need to do some research on what crypto mining is, and what wallets, transactions, etc are. For this we are mining coins -- Monero specifically -- that use the CryptoNote algorithm. For more on CryptoNote coins, visit here:
https://cryptonote.org/coins
(Strange, for an organization that supposedly keeps track of CryptoNote, it's really lacking in .. err.. CryptoNote coins. There's so many more than the site lists... I think somebody's getting paid....)

1. Run XMR-STAK.exe for the first time. You will be prompted to answer a few questions. For the first question of what currency you're mining, just put in "monero". For the rest of the answers, you will only know them if you have a wallet, and a pool chosen for mining. (Google is your friend).
2. Let it run for about a couple of minutes, and press "H" on your keyboard. This will tell you if your GPU is indeed hashing. If not, you did something wrong. If it shows <na> in any of the fields, you did something wrong.
3. Now shut down XMR-STAK.exe by pressing CTRL+C.
4. Inside the folder that you ran XMR-STAK.exe you'll see that the app generated some extra files. The important one for this tutorial is amd.txt. For advanced users, you'll want to edit config.txt for changing pools, setting up multiple pools, etc.
5. Open amd.txt with a text editor.. if you double click it should open up the file in notepad by default. Inside the file, you'll see a single setting for your GPU. You'll want to insert a second thread for your GPU and use the following settings:
   

   "gpu_threads_conf" : [
     { "index" : 0,
       "intensity" : 400, "worksize" : 8,
       "affine_to_cpu" : 0, "strided_index" : true
     },
     { "index" : 0,
       "intensity" : 400, "worksize" : 8,
       "affine_to_cpu" : 1, "strided_index" : true
     },
   ],
   

   You'll notice I have affine_to_cpu set to 0, and 1 respectively. The CPU I'm using has 2 cores, so in a nutshell, each thread is being "managed" by each core of the CPU.

6. Save the amd.txt file you just edited.
7. Now we create a batch file to run the miner. Because there's still one more set of settings we want before the miner actually runs.
   Create a file and name it "whateveryouwant.bat". I named mine "RunThisFirst.bat". Now edit the file by right-clicking on it, and select "Edit". You want the following inside your batch file:
   

   setx GPU_FORCE_64BIT_PTR 0
   setx GPU_MAX_HEAP_SIZE 98
   setx GPU_MAX_ALLOC_PERCENT 100
   setx GPU_SINGLE_ALLOC_PERCENT 100
   xmr-stak.exe --noCPU
   

   These settings are to make sure your GPU will be using 100% or close to 100% of all resources available to it. (That's the TL;DR version).
   Save the file.

8. Now run the newly created batch file. It'll pop up a window telling you, you need to be an admin, yada yada, click on yes.
9. Now you should see similar numbers that I have here:
   ![xmr-stak-monero-hash.jpg]()

Note: This is for this EXACT model of card. Not all manufacturers and card models, even if they all use the rx-550 GPU are created equal. Ram size, memory manufacturer, and manufacturer tweaks will alter the performance of the cards. So if you're using a different brand/model and using this "Tutorial" (I say this with a grain of salt.. I'm not very good at writing tutorials), don't expect to see exact or even similar hashrates.

If you're reading this, and you are actually new to Crypto and Mining, be aware:

At this stage of the game, you need to mine alt coins, and not the big ones like Ethereum or Monero. Bitcoin, Bitcoin Cash, Zcash, etc are out of your (and my) league. Their network difficulties have gone insane the past 8 months, ever since main stream media started reporting about them, and BOOM, everyone and their mom (and me) started mini mining operations at home. And of course the pro miners just simply added more hashing power to take advantage of the insanely huge upswings in coin prices across the board.

UPDATE - increase in hashrate by 40-60 h/s using xmrig. Same power consumption.