Hyper-Threading is A Performance Feature
Hyper-Threading is the name of Intel technology that allows a single physical processor to operate logically as if it were two processors. Pentium 4 630 processors, the first Intel product with Hyper-Threading support, were released on November 15, 2002. Intel explains Hyper-Threading technology on its website as follows: Hyper-Threading uses processor resources more effectively, allowing multiple threads to be executed simultaneously on each core. Additionally, Hyper-Threading as a performance feature increases processor efficiency and improves the overall performance of multithreaded software. Although each processor is physically on the same chip, they can process different command chains at the same time. Logical processors with Hyper-Threading technology can share only one of the resources such as system bus, firmware and memory per unit time. Therefore, a processor with Hyper-Threading architecture cannot provide the performance of two physical processors, even though it appears to the operating system as a dual-processor system.
Figure 1. An x86-based processor with Hyper-Threading and an x86-based physical dual-core processor
How Does Hyper-Threading Work?
Assume that two threads will be processed on a single-core processor.
Figure 2. Processing a thread on a processor without Hyper Threading
On any processor that does not support Hyper Threading technology, threads will be processed sequentially with the First in First out logic.
Figure 3. Thread processing on a processor with Hyper Threading
If the processor supported Hyper Threading technology, threads would be processed simultaneously as if there were two separate processors. However, the processor with Hyper Threading technology will act as two logical processors of a single processor, since there are not two physical processors. For this, both the job to be done at that moment and the operating system on which that job is carried out must support the Hyper-Threading feature. Otherwise, the processing will be performed sequentially on a single processor.
Figure 4. Processing two threads on a physical dual-core processor without Hyper-Threading
If we consider that the same process occurs on a processor that does not support dual-core Hyper Threading technology, the two threads would pass through the processors separately. Of course, the performance of two different processors is superior to the processor that supports Hyper Threading technology. However, there should be no processing priority between threads.
Figure 5. Processing 4 threads on a physical dual-core processor with Hyper-Threading
In this case, 2 of the 4 threads will be processed on one processor and the other 2 will be processed on the other processor.
To explain the Hyper-Threading feature in another way, as seen in the figure below, while command chains are distributed on different physical processors in a system with dual physical processors, in my Hyper-Threading supported system, two different command chains can be processed simultaneously on the same processor. (Simultaneous Multithreading)
Figure 6. Physical and logical processing of threads processed on a Hyper-Threading enabled processor on a single-core and 2-core processor
**System Requirements for Using Hyper Threading**
A processor that supports Intel HT Intel HT Technology enabled chipset Intel HT Technology enabled system BIOS Intel HT Technology enabled optimized operating system.
On a computer with Hyper-Threading, when viewed from the device manager, two processors appear for each physical processor in the system. For example; Although my computer with an Intel Core i5 M 560 processor physically has 2 different processors, it actually has 4 different logical processors.
Figure 7. Processor status of a computer with Hyper-Threading feature on Win 8.1 Pro in the device manager
When you access the task manager with Ctrl+Alt+Del, two logical processor graphs appear for each physical process in the performance monitor.
Figure 8. Processor status of a computer with Hyper-Threading feature on Windows 8.1 Pro in the task manager
Software Support
In order for the processor to use the Hyper-Threading (HT) feature, it must be supported software-wise, both at the level of the program to be used and the operating system on which the program will be run. Naturally, in order for two or more command chains to be processed simultaneously, they must not use the same resources at the same time. Windows XP SP1 and later Windows platform operating systems and Linux Kernel 2.4 and later Linux derivatives support the Hyper-Threading feature.
