The rules behind the answers. These are the details that cause most wrong purchases.
AMD AM4 cooler mounting (stock AMD backplate)
CPU coolers that mount on an AM4 board using AMD's standard backplate / retention hardware.
- Low-profile coolers that replace the stock AMD backplate (e.g. Noctua NH-L9a-AM4, NM-AM4-L9aL9i kit) fit AM4 but not AM5.
- Noctua notes some AMD boards violate AMD's 96x114 mm keep-out zone; check RAM and VRM-heatsink clearance with large coolers.
Source: Noctua: AMD AM5 - all you need to know
AM4-only cooler mounting with a custom backplate
Coolers that require removing AMD's stock AM4 backplate and fitting their own; they work on AM4 only.
- Noctua: the NH-L9a-AM4 and NM-AM4-L9aL9i require replacing the standard AMD backplate with a custom one, which isn't possible on AM5. Use the NH-L9a-AM5 (or the NM-AM5-L9aL9i kit) on AM5.
Source: Noctua: AMD AM5 - all you need to know
AMD AM5 cooler mounting
CPU cooler mounting on AM5 boards; keeps AM4's stack-up height and backplate thread pattern.
- Noctua: AM4 and AM5 share the same stack-up height and backplate thread pattern, so coolers that use the standard AMD backplate carry over; Corsair likewise says AM5 uses the same cooler bracket size as AM4.
- Exception: coolers that replace the AMD backplate (Noctua NH-L9a-AM4, NM-AM4-L9aL9i) cannot be fitted to AM5.
- Older Noctua coolers without AM4 hardware need the NM-AM5/4-MP83 or NM-AM5/4-MP78 kit (free with proof of purchase).
- Offset mounting bars (e.g. Noctua's AM5 offset bars) are optional accessories that shift the heatsink toward the CPU hotspot; they are not required for fitment.
Source: Noctua: AMD AM5 - all you need to know
Intel LGA1200 / LGA115x cooler mounting
CPU cooler mounting shared by Intel LGA1200 and LGA1150/1151/1155/1156 boards.
- Not the same as LGA1700/LGA1851: coolers listed only for LGA1200/115x need LGA1700 mounting hardware for newer Intel boards.
- Noctua: the NH-L9i-17xx's thicker base raises mounting pressure too much for LGA115x/LGA1200 and may cause irreversible damage; use the original NH-L9i there.
Source: Noctua FAQ: Why is the NH-L9i incompatible with Intel's LGA1700/LGA1851 socket?
Intel LGA1700 cooler mounting
CPU cooler mounting on LGA1700 (12th-14th Gen) boards; different hole spacing and stack-up height from LGA1200/115x.
- Coolers designed for LGA1200/115x do not fit without LGA1700 hardware. Noctua sends free NM-i17xx-MP83 / NM-i17xx-MP78 upgrade kits (by mounting pitch); Corsair sells the CW-8960091 LGA1700 Retrofit Kit for coolers such as the H150i RGB PRO XT.
- Noctua: the original NH-L9i cannot be used on LGA1700/LGA1851 (it would sit too low); use the NH-L9i-17xx instead. The NH-L9i-17xx must not be used on LGA115x/LGA1200.
- To check a Noctua cooler: if the box specs mention LGA1700, or the Intel parts include the NM-IBP4 backplate, LGA1700/LGA1851 parts are included.
Source: Noctua: Intel LGA1700 - all you need to know
Intel LGA1851 cooler mounting
CPU cooler mounting on LGA1851 (Core Ultra 200S) boards; mounting holes are in the same positions as LGA1700.
- Intel: LGA1700 and LGA1851 mounting holes are in the same locations, so LGA1700 thermal solutions fit LGA1851 without modification. Intel says this covers mounting only; confirm thermal/power suitability with the cooler maker.
- Noctua: all LGA1700-compatible Noctua coolers and mounting kits are also compatible with LGA1851.
- Optional offset mounting (e.g. Noctua NM-IMB8 bars listed for the NH-D15 G2 on Core Ultra 9 285K / 7 265K) is a performance accessory, not required for fitment.
Source: Intel: Are cooling solutions designed for LGA1700 compatible with LGA1851 socket?
AMD Socket AM4 (CPU socket)
AMD desktop socket for Ryzen 1000-5000 series processors; AM4 boards use DDR4 memory.
- AMD: not all processors are supported on every chipset, and support may require a BIOS upgrade. Check the board maker's CPU support list for the minimum BIOS before buying.
- Ryzen 5000 runs on X570, B550, A520 and on 400-series boards (X470, B450) per AMD's chipset table, but a 400-series board whose BIOS predates Ryzen 5000 must be updated before it will boot one.
- On 300-series boards (X370, B350, A320) AMD marks Ryzen 5000 as 'Selective Beta BIOS update needed' - only some boards got that BIOS.
- AM4 processors do not fit AM5 boards and AM5 processors do not fit AM4 boards.
Source: AMD Socket AM4 chipsets page
AMD Socket AM5 (CPU socket, LGA1718)
AMD desktop socket for Ryzen 7000, 8000 and 9000 series processors; DDR5 memory only.
- AMD: all Socket AM5 motherboards (600 and 800 series chipsets) are compatible with all Socket AM5 processors.
- AMD: a BIOS update may be required for Ryzen 8000 and 9000 series processors on 600-series (X670E, X670, B650E, B650, A620) boards.
- AM5 is DDR5-only; DDR4 memory from an AM4 build cannot be reused.
- AM5 processors do not fit AM4 boards.
Source: AMD Socket AM5 chipsets page
Intel LGA1700 (CPU socket)
Intel desktop socket for 12th, 13th and 14th Gen Core processors on 600- and 700-series chipset boards.
- Intel: 600-series and 700-series boards require a BIOS update to boot 13th and 14th Gen Core processors, and may need one when moving between 12th, 13th and 14th Gen. Update the BIOS before swapping the CPU.
- Each LGA1700 board supports either DDR4 or DDR5, never both (e.g. 'D4' / 'DDR4' model variants). The CPUs support both, so buy RAM to match the board.
- Intel recommends a BIOS with microcode 0x12F or later for 13th/14th Gen desktop processors (Vmin Shift instability issue).
- LGA1700 processors do not fit LGA1851 (Core Ultra 200S) boards, and Core Ultra 200S processors do not fit LGA1700 boards.
Source: Intel: Required BIOS Updates for Intel 600 and 700 Series Chipset with 13th and 14th gen
Intel LGA1851 (CPU socket)
Intel desktop socket for Core Ultra 200S (Series 2) processors on 800-series chipset boards (Z890, B860); DDR5 only.
- Intel: Core desktop processors (12th-14th Gen, LGA1700) and Core Ultra desktop processors (Series 2, LGA1851) are not cross-compatible.
- Core Ultra 200S processors support DDR5 only.
Source: Intel: Are cooling solutions designed for LGA1700 compatible with LGA1851?