Hardware · Topic 8 of 13
CPUs and Cooling
Understand CPU sockets, cores and threads, x86, x64 and ARM, virtualization support, and how heat sinks, fans, paste and liquid cooling protect a CPU.
- 5 min
- LGA has pins on the socket; PGA has pins on the CPU.
- The CPU, socket, chipset and firmware must all be compatible.
- x64 CPUs run 64 bit systems; ARM is power efficient and common in mobile devices.
What it is
The central processing unit (CPU) runs instructions for the whole computer. Choosing and installing one means matching the socket, understanding its key traits and removing the heat it makes.
A CPU without proper cooling will slow itself down and, in the worst case, shut the system off to protect itself.
How it works
Sockets
The CPU socket on the motherboard must match the processor. Two layouts are common.
| Layout | Description |
|---|---|
| Land grid array (LGA) | The pins are on the motherboard socket; the CPU has flat contacts |
| Pin grid array (PGA) | The pins are on the CPU; the socket has holes |
Intel desktop processors have long used LGA. AMD used PGA for older desktop CPUs and uses LGA on its newer desktop socket. The maker and the generation both decide the socket, and the chipset and firmware must also support the CPU.
A multisocket motherboard, such as a dual socket board, holds two or more physical CPUs that share the system memory. These boards are used in servers and workstations that need many cores. The CPUs must be matching models that the board supports, and the operating system must support more than one processor.
Architecture
| Architecture | Notes |
|---|---|
| x86 | 32 bit instruction set; limited to about 4 gigabytes (GB) of memory |
| x64 | 64 bit extension of x86; the common type for desktops, laptops and servers |
| Advanced RISC Machine (ARM) | Power efficient design used in phones, tablets and some laptops and servers |
A 64 bit operating system needs a 64 bit CPU, and software built for x86 or x64 does not run natively on ARM without help.
Key CPU traits
- Cores: separate processing units on one chip. More cores help with many tasks at once.
- Threads: a core can run two threads at a time with simultaneous multithreading, branded as Hyper-Threading on Intel.
- Clock speed: measured in gigahertz (GHz); higher is faster for the same design.
- Cache: small, very fast memory on the CPU, in levels L1, L2 and L3.
- Integrated graphics: a graphics processor built into some CPUs, so a separate card is optional.
- Thermal design power (TDP): a rating of the heat the CPU makes, which guides the cooler choice.
- Virtualization support: hardware features that let virtual machines run well; they are sometimes called Intel VT-x and AMD-V, and are often turned on in the firmware settings.
- Overclocking: running a CPU faster than rated, which raises heat and can shorten life.
Cooling
The main parts of cooling are shown below.
| Part | Role |
|---|---|
| Heat sink | A finned metal block that draws heat from the CPU |
| CPU fan | Blows air through the heat sink |
| Thermal paste | A thin layer between CPU and heat sink that fills tiny gaps and carries heat across |
| Liquid cooling | A pump moves liquid through a block on the CPU to a radiator with fans; quieter and more effective for hot CPUs |
| Case fans | Move air through the case, usually in at the front and out at the rear |
| Passive cooling | A heat sink alone with no fan, for low power chips |
A cooler that is too weak causes throttling, where the CPU lowers its speed to stay cool.
Installing a CPU and cooler
- Power off, unplug and use electrostatic discharge (ESD) protection.
- Lift the socket lever and open the retention frame if present.
- Match the mark (a small triangle) on the CPU to the mark on the socket, and lower it in without force.
- Close the frame and lock the lever.
- Apply thermal paste if the cooler does not have it already. A small amount is enough.
- Fit the cooler and tighten it evenly, then plug the fan into the CPU fan header.
- Start the computer and check the temperature in the firmware screen.
Never force a CPU into a socket, and never power on without a cooler fitted, because the CPU can overheat quickly.
Airflow in the case
Cool air should enter at the front and bottom and leave at the rear and top. Cable clutter, blocked vents and dust reduce airflow. Clean dust filters on a regular schedule.
What to remember for the exam
- LGA has pins on the socket; PGA has pins on the CPU.
- The CPU, socket, chipset and firmware must all be compatible.
- x64 CPUs run 64 bit systems; ARM is power efficient and common in mobile devices.
- Cores run tasks in parallel; hyper threading lets a core run two threads.
- Virtualization support may need to be enabled in the firmware.
- Thermal paste fills gaps between CPU and heat sink.
- Liquid cooling moves heat to a radiator with a pump.
- Throttling means the CPU slows itself down because of heat.
Common mistakes
Using too much thermal paste. A thin layer works better, and excess can spill onto the board.
Forgetting to plug in the CPU fan. The system may shut down, or warn of a fan fault.
Assuming any CPU fits any board. The socket must match, and firmware support is also needed.
Bending pins. On LGA boards, the socket pins are delicate. Never touch or tilt them.
Ignoring dust. Clogged heat sinks cause heat, noise and slow performance.
Check yourself
What is the difference between LGA and PGA?
In LGA the pins are on the motherboard socket, while in PGA they are on the CPU.
What does thermal paste do?
It fills tiny gaps between the CPU and the heat sink so that heat passes across well.
What is throttling?
The CPU lowers its speed to cut heat when cooling is not enough.
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