There are two ways cores on a physical machine affect ArcGIS Server.
1. Licensing - Every license of ArcGIS Server is for 4 CPU cores.
2. Performance - The System Design Strategy guide states that peak throughput for ArcGIS Server is reached if total map services instances are 3 - 5 (average 4) per core. Therefore, on a 4 core machine you could get peak throughput by configuring a total 16 map services instances.*
Many computers today have a hyper-threaded CPU which show more number of logical processors than cores. See image below.
On such machines, is ArcGIS Server licensing and performance to consider this as a 4 core or a 8 core machine?
For licensing - should I purchase two licenses?
For performance - can I configure 16 or 32* map service instances?
*4 map service instances per core may not always be the case and this number may change as per you service contents and configuration. For more details, refer to the Server Software Performance section of the System Design Strategy guide.
A per-core-license is for the physical core and not for the logical.
Attention: in a virtualized environment the license would be on vCPU's - whatever there is behind that number.
HyperThreading does not double the performance of your machine. In best cases there is a little gain ( 15%-30% ). For more infos see: Will Hyper-Threading Improve Processing Performance
If ArcGIS Server can really benefit from HyperThreading is a good question. In my opinion ArcGIS Server can be single-threaded (high isolation) or multi-threaded (low isolation) (see: Process threads). If I'm getting this right, I suppose: to take advantage of HyperThreading you should use low isolation (on a physical machine).
My follow-up question is about whether the logic of 4 cores for 1 license is applicable for ArcGIS Server extensions also, such as Image Server?
For example, we have ArcGIS Server Standard Enterprise and Image Server extension on one server, which has 8 cores. So it means we need 2 licenses (or 2 times the cost of one ArcGIS Server Standard Enterprise license). Do we need 2 licenses for Image Server as well for 8 cores, or is the extension license based on per server or host?
This is less a follow-up than a completely new question, but yes, extensions are licensed using the same model as the base software -- 8 CPU cores = two 4-core licenses. This could be addressed to your marketing/sales rep or a contracts rep if you need further clarification (legal stuff is better asked of corporate representatives than random users on GeoNet).
I don’t feel that the question is answered.
If the machine has 6 cores and 12 logical processors, how this is considered for ArcGIS Server? Does the ArcGIS Server work based on the cores or logical processors?
So here's what the the documentation says (my emphasis):
The ArcGIS Server component of ArcGIS Enterprise is licensed by CPU cores. Cores are part of the computer’s CPU (Central Processing Unit) that determines the number of instructions that can be processed at a given time. A 4-core processor can handle four sets of instructions at once. Many modern CPUs further support a technology known as hyper-threading that allows a single core to run multiple concurrent sets of instructions. Hyper-threads do not count towards the licensed cores. Licensed cores can be counted by physical cores or virtual cores, whichever is more advantageous to you. The minimum purchase for ArcGIS Enterprise is an “up-to-4 core” license* which can be installed on a two or four core machine. If your machine has more than 4 cores (physical or virtual), you can purchase additional cores, or virtualize the machine so that the 4-core license of ArcGIS Enterprise is only installed on 4 (virtual) cores and thereby satisfies the license requirement. If a 4-core license is installed on an 8-core physical machine without virtualization, then ArcGIS Enterprise will use all 8 cores and would be in violation of the license agreement until you purchase a license for the four “additional cores”.
Note that early generations of Microsoft Azure VMs used physical core equivalents, listed in terms of “cores”, whereas later generation Microsoft Azure VMs use vCPUs that correspond to a hyper-thread. It is important to calculate the physical core equivalent correctly based on the specific generation of VM that is chosen.
*Note: ArcGIS Enterprise requires a minimum initial license purchase of 4 cores per physical location. The minimum for ArcGIS Enterprise Workgroup is 2 cores. Additional cores may be licensed in 2-core increments. ArcGIS Enterprise Workgroup is not licensed for multi-machine environments
If you find this unclear, you should contact Customer Service, Tech Support, or your local marketing representative.
I’m convinced that having our enquires answered via forum is much more conformable, transparent, and robust than having one-one discussion with resellers. We are not asking here about the prices but focusing on how the technology works.
All what we wanted to know here if esri licensing is based on the number of cores OR the number of logical processors? according to the case below, is it 6 cores or 12?
Many thanks Michael for the precise answer