Measuring Temperatures with Thermal Probes and External Sensors
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A Central Processing Unit (CPU) is the most complex component in a digital computer. It’s a necessary component, which basically does
all of the work in a computer. As technology advanced, these CPUs architecture became more and more complex, and their ability was significantly improved. But this came at a price: increased production of heat, which can threaten your CPU's performance.
It's completely understandable that integrated circuitry components produce heat. Components like capacitors, resistors, and transistors produce the heat because of high voltage load. In a personal workstation computer system there are multiple components which can and will produce heat. For example, the most important are the CPU, hard drive(s), motherboard (Northbridge, Southbridge, other components), memory, PSU (Power Supply Unit), and Graphical Processing Units (video cards, etc), which comprise basically everything.
Your whole system, once it's plugged in and powered on, is working. Even when idling, it is still carefully reacting to whatever choices you make. It is really important to understand that an electric component has a lifespan. Manufacturers try to match this lifespan. This lifespan is accurate most of the time, but only if your system is kept under ideal conditions-meaning it is not overheating, satisfactory humidity and pressure levels, etc. Under the proper conditions, your computer will live happily longer than its maximum rated lifespan.
Temperatures can be measured with thermal probes, diodes, and sensors. There are two types of thermal diodes. The first uses semiconductors or thermocouples (based on Peltier-Seebeck effect), and the second is based on some vacuum tubes (the principle is called the Edison effect). Basically they can have many purposes, but for us their sensory one is important. A thermal diode can measure temperatures. That is why they are embedded onto microprocessors (in our case onto the CPU) to monitor their on-die temperature. Okay, enough electronics, let's move on.
Modern central processing units incorporate two thermal diodes of this kind. One monitors the on-die temperature, and the second prevents the processor from frying by controlling throttling. This detailed information is available to the public in Intel's official data sheets. In them, they clearly explain their reasons as well as the usage for these two diodes.
The first one is located somewhere in the silicon (according to some information it is located in one of the corners of the processor). It measures and monitors on-die temperatures, then reports them to the user on motherboards that support the ability to read (get) this information.
The second diode's purpose is more special. Basically, there is an on-die temperature control variable provided to a thermal actuator that throttles the integrated circuitry by reducing its clock cycles and power usage. This second diode acts as a simple thermal sensor and measures the on-die temperature of the processor. These readings are constantly compared with the temperature control variable, and if the temperature is higher than the maximum allowed operating temperature, it reports to the thermal actuator, and the throttling procedure begins.
It is important to understand that these two diodes are acting individually and are placed on different places on the core. They are not even on the same silicon layer, as specified by Intel. We can assume that a central processing unit will not dissipate heat the same across its whole body so there will be areas where the temperature will be higher and lower.
Further, we don't know the position of these two diodes. We can only assume that the second diode, which measures and controls the throttling, is located somewhere in the middle of the core where it's near the center of the processor. This place should reach peak temperatures. The first diode, which reports the core temperatures to the user, may be placed elsewhere. This is why sensor reports are unreliable. It is possible that when your sensor reports 70C the core temperature is over 90C. Of course this example is banal, but it was just an example to simplify this whole procedure. Summing this up, we cannot predict when a system will throttle, only assume.
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