For the POC phase:
Windows
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server
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,
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4GB+ RAM,
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50GB+ HDD
For Production:
Medium Load option
Windows 2012 R2 or Higher Standard Edition/2008 R2 Ent. +,
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16 GB RAM, Dual Core Intel Xeon E3 or similar, 5 GB free disk space (mainly for logs).
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SSD with a R/W speed of at least 50MB/s.
One server supports up to ~7k concurrent users
High Load option
Win2012 R2 or Higher, Quad Core Xeon or similar, 24GB ram, 25G disk space.
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SSD/Raid with R/W speed of at least 100MB/s.
One server supports up to ~18k concurrent users
Extreme High Load option
Win2012 R2 or Higher, 2.3 GHz Intel Xeon® 16 Cores, 64GB ram, 50G disk space.
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SSD/Raid with R/W speed of at least 200MB/s.
One server supports up to ~40k concurrent users