Windows 8.1 /write very very very slowly

Just switched from Windows 7 Home Premium to 8.1 Pro and suddenly my scripts which write a lot of text are 5-10 slower writing. I built a test and confirmed it is slower than a similar yet inferior machine. My new Windows Build has very fast Passmark scores.

Code:

alias SpeedWrite { var %1 = C:\Users\Public\Documents\SpeedWrite.txt, %2 = 1, %3 = $ticks | if ($exists(%1)) { .remove -b %1 }
  while (%2 < 200) { write %1 $str($r(A,Z),999) | inc %2 }
  echo Complete: $calc($ticks - %3) $+ ms
}

Win 8.1 Pro i7-4790 mIRC 7.32 similar with 6.21 and 7.41
=Kingston HyperX SSD=
Complete: 1219ms
Complete: 1157ms
Complete: 1172ms
Complete: 1360ms
=WD 1TB HDD=
Complete: 1172ms
Complete: 1000ms
Complete: 984ms
Complete: 1203ms
=Seagate 3TB HDD=
Complete: 1078ms
Complete: 1000ms
Complete: 968ms
Complete: 1109ms

Win 10 Pro i3-3225 Very Old WD 1TB HDD mIRC 7.32
Complete: 219ms
Complete: 266ms
Complete: 235ms
Complete: 188ms

The only difference being 8.1? How can i resolve this slow write speed...

Thanks for your bug report. I don't have Windows 8, however the method for writing files is identical on all versions of Windows, so that will not make a difference. Testing under Windows 10, each run took around 1700ms. I then turned off Windows defender anti-virus scanning and it dropped immediately to 250ms. If you do the same, does that resolve the issue?

Good work around, Thanks! Windows Defender on...
Complete: 1266ms
Complete: 1031ms
Complete: 1109ms
Complete: 1063ms
Windows Defender off...
Complete: 109ms
Complete: 125ms
Complete: 110ms
Complete: 109ms

This is my first time ever enabling Windows Defender. Thus I've never experienced this. Is there a way to give mIRC the green light, so Windows Defender can be on without this lag.

I'll answer my own question:
In Windows Defender Settings > Excluded processes > Browse to mIRC Folder > mIRC.exe > Add

Problem Solved.

Similar fix in Windows7 with Microsoft Security Essentials. I added a time-echo above the while-loop, and found it often was even slower to delete the existing speedwrite.txt than to write the 200 lines to it.

Once I added the write folder to Settings/Excluded-files-and-locations, the speed was much faster. At least in MSE, the change in write/delete speed is inherited into subfolders too.