Almost every part in a PC has one or two things it must match, and a build with one mismatch is a build that does not boot, does not fit, or runs slower than it should. Online compatibility checkers catch the obvious ones. The problems that reach our bench in Somerville are the ones they miss: a motherboard that shipped with a BIOS too old for the CPU, a memory kit that is not on the board's list, a graphics card that fits on paper and not with the power cable plugged in. Here is the full compatibility check we run before a part is ordered, in the order we run it, and how to run it yourself.
Each one is a spec sheet comparison. The spec sheets are free; the mistakes are not.
The processor and motherboard have to share a socket: AM5 for current Ryzen (7000, 8000 and 9000 series), AM4 for older Ryzen, LGA1851 for Intel Core Ultra 200S, LGA1700 for 12th through 14th generation Core. The chipset then decides features, not compatibility: any B850, X870 or X870E board takes any AM5 chip. Tom's Hardware's motherboard buying guide walks through sockets and chipsets if the names are new to you, and our own motherboard guide covers which chipset to buy.
A board can list your CPU as supported and still not boot with it, because the support was added in a BIOS update after the board left the factory. Every board maker publishes a CPU support list with the minimum BIOS version per chip. If the board on the shelf is older than the CPU, you need a board with a BIOS flash button (USB BIOS FlashBack, Flash BIOS Button, Q-Flash Plus or BIOS Flashback, depending on the brand) or an older CPU to update with. This is the single most common "dead on arrival" build we see, and the parts are always fine.
DDR4 and DDR5 use different slots, so the board decides the generation. After that, use the board's memory qualified vendor list (QVL), which ASUS, MSI, Gigabyte and ASRock all publish per board; ASUS's support article shows where to find it. A kit that is not on the list usually works, but "usually" is the problem: AM5 boards in particular can refuse to run an unlisted kit at its rated speed or at all. Kingston's and Corsair's memory finders take the board model and return kits they have validated, which is a second opinion worth thirty seconds. Our DDR4 vs DDR5 guide covers speed and capacity once you know the generation.
Three numbers: card length, card thickness in slots, and the case's maximum for each. Then add the power cable. Nvidia's RTX 5080 Founders Edition page lists the card at 304 mm long, 137 mm wide and two slots thick, and asks for 36 mm of extra clearance for the 16-pin power connector. Partner cards from ASUS, MSI, Gigabyte and others are frequently longer and three or even four slots thick, so use the exact model's dimensions, not the reference card's. Corsair's case-fit guide explains the same checks from the case side. Our case sizes guide has the clearance numbers for common case classes.
Two parts to this. First, the card maker's required system power: Nvidia lists 650 W for the RTX 5070, 750 W for the RTX 5070 Ti, 850 W for the RTX 5080 and 1000 W for the RTX 5090, and AMD lists 750 W for the RX 9070 XT. Second, the connectors: current Nvidia cards use a 16-pin 12V-2x6 plug (an adapter from 8-pin cables ships in the box), while the RX 9070 XT uses two 8-pin cables. An older supply may have the watts and not the cables, or the cables and not the transient tolerance. Our PSU sizing guide covers the ATX 3.1 side.
The cooler must ship with a bracket for your socket (AM5 and LGA1851 are both current, and older coolers may need a free bracket from the maker). A tower air cooler must clear the case's maximum cooler height, and tall coolers can also overhang the first memory slot, so check the cooler's memory clearance against the height of your kit. For an all-in-one liquid cooler, match the radiator size to the case's supported positions, not just to the case in general. Our air vs liquid guide covers which type to buy.
Count the M.2 slots, note the PCIe generation of each, and read the footnotes. On many boards, using a specific M.2 slot disables two SATA ports or drops a secondary PCIe slot to fewer lanes. That is not a defect, it is how the lanes are shared, but it surprises people who planned on four SATA drives and two NVMe drives. Also check that the drive length (2280 is standard) is supported by each slot you intend to use.
ATX supplies fit ATX cases; small form factor cases need SFX or SFX-L units. Compact cases list a maximum supply length, and high-wattage ATX units are often 160 to 180 mm long. Confirm the supply has enough of the right cables for the build: two CPU power connectors on many boards, enough SATA connectors for the drives, and the native 16-pin cable if you are using an RTX 50 card.
Online parts list tools with a compatibility filter are good at what they do. It is worth knowing exactly what that is.
None of that is a criticism of the tool. It works from published specs, and the failures above live in footnotes, firmware and physical clearances that no database captures. It is why a parts list that passes every automated check can still arrive at our counter as a no-boot build, and why we do the eight checks by hand on every build we quote, whether we supply the parts or you bring your own to our PC assembly service.
Copy this into your notes and fill in the right-hand column from the spec sheets before you order.
| Check | Where to look | Pass condition |
|---|---|---|
| Socket | CPU spec page, board spec page | Same socket (AM5, AM4, LGA1851, LGA1700) |
| BIOS version | Board's CPU support list | Board BIOS is at or above the minimum for the CPU, or the board has a flash button |
| Memory | Board QVL, Kingston or Corsair memory finder | Right generation, one matched kit, on the list, two slots populated |
| Graphics card size | Card spec page, case spec page | Card length + cable clearance under the case maximum with fans installed; thickness fits the slots |
| Graphics card power | Card spec page, PSU spec page | PSU meets the card's required system power and has the native connectors |
| Cooler | Cooler spec page, case spec page, memory height | Socket bracket included, height under the case maximum, radiator size supported in the chosen position |
| M.2 and storage | Board manual, storage section | Enough slots at the right generation, lane-sharing footnotes read, drive length supported |
| Power supply fit | PSU spec page, case spec page | Correct form factor, length under the case maximum, enough cables |
⚡ Want the list checked by someone who does this daily? Send us your parts list before you order, or bring the boxes in after. We run all eight checks, flag anything that will not work, and build it right the first time.
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Match the CPU socket to the motherboard, confirm the board's BIOS supports the CPU (or that the board has a flash button), buy memory of the right generation from the board's QVL as one matched kit, compare graphics card length and thickness plus power cable clearance to the case, confirm the power supply meets the card's required wattage with native connectors, check cooler height and socket bracket, read the M.2 lane-sharing footnotes, and confirm the power supply form factor fits the case.
They are accurate for what they check: socket, memory generation, board form factor, wattage totals, and published length and height limits. They cannot see the board's shipped BIOS version, whether a memory kit is on the QVL, clearance with a front radiator installed, transient handling of an older supply, or M.2 lane sharing. Treat a green check as necessary, not sufficient.
The most common reason is a motherboard BIOS that predates the CPU. The parts are compatible on paper, but the board cannot recognize the chip until its firmware is updated, which needs a flash button or an older supported CPU. The second most common reason is a memory kit that is not on the board's QVL or two kits mixed together.
Check the generation first (DDR4 boards take only DDR4, DDR5 boards only DDR5), then look up the board's memory QVL on the maker's support page, or use Kingston's or Corsair's memory finder with the board model. Buy one matched two-stick kit rather than combining kits.
Compare the exact card model's length and slot thickness to the case's maximums, subtract any front radiator or fans, and allow for the power cable: Nvidia asks for 36 mm beyond the RTX 5080 Founders Edition's 304 mm length for the 16-pin connector. Partner cards are often bigger than the reference design.
If it is below the card maker's required system power (650 W for an RTX 5070 up to 1000 W for an RTX 5090, 750 W for an RX 9070 XT), lacks the native connectors, or is an older pre-ATX 3.0 unit that may not tolerate transient spikes, yes. We test the existing supply before any graphics card upgrade.
Send us the parts list or bring the boxes. We run every compatibility check, fix what will not work, and hand you a PC that boots the first time.
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