Basically, a core can be considered as a small processor built into the main processor that is connected to a socket. Applications should support parallel computations to use multicore processors rationally.
Hyper-threading is a technology developed by Intel engineers to bring parallel computation to processors that have one processor core. The debut of hyper-threading was in when the Pentium 4 HT processor was released and positioned for desktop computers.
An operating system detects a single-core processor with hyper-threading as a processor with two logical cores not physical cores. Similarly, a four-core processor with hyper-threading appears to an OS as a processor with 8 cores. The more threads run on each core, the more tasks can be done in parallel. Modern Intel processors have both multiple cores and hyper-threading. Hyper-threading is usually enabled by default and can be enabled or disabled in BIOS.
A vCPU is a virtual processor that is configured as a virtual device in the virtual hardware settings of a VM. A virtual processor can be configured to use multiple CPU cores. A vCPU is connected to a virtual socket. CPU overcommitment is the situation when you provision more logical processors CPU cores of a physical host to VMs residing on the host than the total number of logical processors on the host.
NUMA non-uniform memory access is a computer memory design used in multiprocessor computers. The idea is to provide separate memory for each processor unlike UMA, where all processors access shared memory through a bus.
At the same time, a processor can access memory that belongs to other processors by using a shared bus all processors access all memory on the computer. A CPU has a performance advantage of accessing own local memory faster than other memory on a multiprocessor computer.
These basic architectures are mixed in modern multiprocessor computers. Processors are grouped on a multicore CPU package or node.
Processors that belong to the same node share access to memory modules as with the UMA architecture. Also, processors can access memory from the remote node via a shared interconnect. Processors do so for the NUMA architecture but with slower performance. This memory access is performed through the CPU that owns that memory rather than directly. An example. Each CPU has 6 processor cores. This server contains two NUMA nodes. The total number of physical CPU cores on a host machine is calculated with the formula:.
If hyper-threading is supported, calculate the number of logical processor cores by using the formula:. Finally, use a single formula to calculate available processor resources that can be assigned to VMs:.
For example, if you have a server with two processors with each having 4 cores and supporting hyper-threading, then the total number of logical processors that can be assigned to VMs is. As for virtual machines, due to hardware emulation features, they can use multiple processors and CPU cores in their configuration for operation.
For example, if you configure a VM to use 2 vCPUs with 2 cores when you have a physical processor whose clock speed is 3. The maximum number of virtual processor sockets assigned to a VM is If you want to assign more than virtual processors, configure a VM to use multicore processors. The maximum number of processor cores that can be assigned to a single VM is in vSphere 7. A virtual machine cannot use more CPU cores than the number of logical processor cores on a physical machine.
CPU hot add. OS CPU restrictions. If an operating system has a limit on the number of processors, and you assign more virtual processors for a VM, the additional processors are not identified and used by a guest OS. Limits can be caused by OS technical design and OS licensing restrictions. Note that there are operating systems that are licensed per-socket and per CPU core for example, Windows Server For older vSphere versions, I recommend using sockets over cores in VM configuration.
Be aware of some configuration features. This automatic configuration is optimal on the underlying physical topology of the server. As a result, VM performance is affected and can degrade. If a guest operating system and other software installed on a VM are licensed on a per-processor basis, configure a VM to use fewer processors with more CPU cores. For example, Windows Server R2 is licensed per socket, and Windows Server is licensed on a per-core basis.
If you use CPU overcommitment in the configuration of your VMware virtual machines, keep in mind these values:. First of all, determine how many logical processors Total number of CPUs of your physical host are needed for a virtual machine for proper work with sufficient performance. Then define how many virtual sockets with processors Number of Sockets in vSphere Client and how many CPU cores Cores per Socket you should set for a VM keeping in mind previous recommendations and limitations.
The table below can help you select the needed configuration. If you need to assign more than 8 logical processors for a VM, the logic remains the same. What is the maximum quantity of cores in a physical processor of a PC that each edition and its corresponding processor architecture of Windows XP supports? What is the maximum quantity of physical processors of a PC that each edition and its corresponding processor architecture of Windows XP supports?
The number of processors you can use depends on the version of Windows XP you use, though there are some caveats. Be sure to know what you're doing before you attempt to set up multiple processors.
Microsoft's licensing policy limits the number of processors Windows supports for its Home and Professional versions, as outlined below. It's important to understand, however, that this is on a per-processor basis, not a per-core basis. This means that, under the licensing policy, a dual- or even quad-core processor counts as a single processorsomething that confused many people in the early days of dual-core technology.
Knowing that, the limit of the number of processors is determined by your version of Windows XP. If you're not sure which version you're running, check the sticker on your computer.
It will say the version there beside your license key; you may right-click "My Computer" and click "Properties. The Home edition of Windows XPthe edition that came with most machines home users bought from the likes of Dell and HP, before Windows Vistasupports only one processor.
This means if you want to install more than one processor and you run Windows XP Home, you may need to switch to Professional, or upgrade Windows to a newer version with support for multiple processors. If you want to use two processors, Windows XP Professional is the way to go.
While this advanced program cannot run more than two processors, this is an improvement over Home. Note that, because dual-core processors count as a single processor, you could theoretically have four cores with this license or even eight, if you are willing to buy two quad-core processors.
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