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Both the Intel Core i7-7700K and Core i7-8700K use desktop DDR4 memory. The i7-7700K is officially rated for DDR4-2133 or DDR4-2400, while the i7-8700K is rated for DDR4-2666. If you need one RAM description that fits either processor, choose a DDR4-2400, 1.2 V, non-ECC UDIMM kit, then verify the motherboard’s DIMM type, supported capacity, BIOS version and qualified-vendor list (QVL). The processors are not interchangeable on the same chipset platform: 7th-generation i7-7700K systems use Intel 100- or 200-series boards, while 8th-generation i7-8700K systems require an Intel 300-series board.
What type of RAM is compatible with the i7-7700K and i7-8700K?
Use unbuffered desktop DDR4 DIMMs, normally sold as DDR4 UDIMMs. DDR4-2400 is the common Intel-rated speed for both CPUs, making it the safest single search term when you have not yet confirmed which processor or motherboard you own. Select non-ECC modules at the standard DDR4 voltage of 1.2 V unless your board documentation specifies another supported setting.
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The i7-7700K has an additional DDR3L option in Intel’s specification, but that does not make DDR3L a universal choice. The i7-8700K specification lists DDR4-2666, not DDR3L. Memory generation, physical keying and voltage are different, so a DDR3L kit cannot be treated as a shared upgrade for both systems.
RAM compatibility is ultimately controlled by the motherboard. A module can meet the processor’s memory specification and still fail because the board does not support its density, rank layout, BIOS version or capacity.
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How do the official memory specifications compare?
Intel’s product specifications and supported-memory tables list these limits for the two processors:
| Processor | Generation | Intel-listed memory | Maximum memory | Channels | ECC support |
|---|---|---|---|---|---|
| Core i7-7700K | 7th generation (Kaby Lake) | DDR4-2133/2400; DDR3L-1333/1600 at 1.35 V | 64 GB | 2 | No |
| Core i7-8700K | 8th generation (Coffee Lake) | DDR4-2666 | 128 GB | 2 | No |
The capacity figures are processor-level maximums from Intel’s 2025 specifications. Your motherboard may impose a lower ceiling, limit the size of each DIMM, or support fewer modules than the processor’s theoretical maximum. Check the board manual rather than assuming that four large modules will work.
Is DDR4-2400 the best shared choice?
Yes, when you want one conservative specification that falls within Intel’s official rating for both CPUs. A DDR4-2400 kit avoids relying on overclocking profiles or on a board automatically reducing a faster kit’s speed.
Look for these terms in the listing:
- DDR4 memory generation
- 2400 MT/s (often marketed as DDR4-2400)
- Desktop UDIMM, not laptop SO-DIMM
- Non-ECC and unbuffered
- 1.2 V nominal voltage
- A capacity and module layout included on your motherboard’s QVL, when available
DDR4-2400 is a data-transfer rate, not a guarantee that every board will run every four-DIMM configuration at that rate. Population rules, firmware and signal quality can cause a board to select a lower setting. The board manufacturer’s manual is the authority for the exact combination.
Can the i7-7700K use DDR3L instead of DDR4?
Intel lists DDR3L-1333/1600 at 1.35 V as an option for the i7-7700K. This applies only to boards designed with DDR3L slots; DDR3L and DDR4 slots are physically keyed differently and cannot accept one another’s modules.
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DDR3L is not a shared solution for the two processors. Intel’s i7-8700K memory specification lists DDR4-2666, so an 8700K platform should be planned around DDR4. Do not force a module into a slot or assume that a board supporting one generation can be converted by changing BIOS settings.
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A DDR4-2666 kit may be usable on an i7-7700K system if the motherboard supports the module and can configure it at a lower speed. Intel’s official i7-7700K rating stops at DDR4-2400, however, so 2666 is not an Intel-rated speed for that processor.
Whether the kit runs at 2400, a lower fallback speed or fails to train depends on the board, firmware, DIMM organization and the number of installed modules. Follow the motherboard specification and QVL instead of assuming that XMP or automatic downclocking will work. If you are buying specifically for a 7700K and want the least uncertainty, choose a kit sold and validated for DDR4-2400.
What RAM speed does the i7-8700K support?
Intel lists DDR4-2666 for the Core i7-8700K. A DDR4-2666 kit is therefore the processor’s listed DDR4 choice, provided the 300-series motherboard supports that capacity and module arrangement.
Lower-speed DDR4, including DDR4-2400, can be appropriate when the board supports it or when you are selecting one kit for both an 8700K and a 7700K system. The processor rating does not override board-specific limits, and a memory profile advertised above 2666 is not an Intel-rated requirement for the 8700K.
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Is DDR5 compatible with either processor?
No. Neither the i7-7700K nor the i7-8700K has a DDR5 memory specification. Both platforms were designed around DDR4-era desktop boards, and the 7700K specification additionally references DDR3L on certain boards.
DDR5 modules use a different electrical interface and key position. A DDR5 motherboard is a different platform, so replacing DDR4 with DDR5 is not an upgrade that can be made by changing the CPU or enabling a firmware option.
Why does the motherboard chipset matter?
The two processors share the LGA1151 package name, but they are not drop-in replacements. Intel places i7-77xx processors on 100- and 200-series chipset boards and i7-87xx processors on 300-series chipset boards.
| Processor family | Intel-associated chipset generation | Upgrade implication |
|---|---|---|
| i7-7700K (i7-77xx) | 100-series and 200-series boards | Confirm the board’s CPU support list and BIOS requirements. |
| i7-8700K (i7-87xx) | 300-series boards | A 300-series board is normally required; an older 100- or 200-series board is not an Intel-supported path. |
Intel’s compatibility guidance states: “The i7-87xx processors are NOT compatible with Intel® 100 and 200 Series Chipset Boards.” Therefore, moving from a 7700K to an 8700K generally means replacing the motherboard as well as checking the RAM. Keeping the old board because both sockets are labeled LGA1151 is not a supported assumption.
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How do I select a compatible RAM kit?
Use this sequence before ordering. It prevents a processor-level specification from being mistaken for a complete system compatibility check.
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- Identify the installed CPU. In Windows, a system-information utility or Task Manager can show the model; the processor’s retail box and BIOS information are alternatives. Record whether the chip is an i7-7700K or i7-8700K.
- Record the exact motherboard model and revision. The model is usually printed on the PCB or shown in the BIOS information screen. A board revision can have a different memory-support list from an otherwise similar model.
- Read the manual’s memory section. Confirm DDR4 versus DDR3L, UDIMM versus SO-DIMM, supported capacities per slot, total capacity, supported speeds and the required slot population order.
- Check the manufacturer’s QVL. Search the board support page for the exact module part number or a validated equivalent. Treat the QVL as evidence of testing, not as a guarantee that every unlisted kit will fail.
- Match capacity to the board’s limits. For an i7-7700K, do not plan beyond the processor’s Intel-listed 64 GB maximum; for an i7-8700K, Intel lists 128 GB. The board may support less.
- Choose a pair or matched kit. Two equal modules normally allow dual-channel operation. Use the slot pair identified by the manual, often marked A2 and B2, rather than guessing from physical proximity.
- Verify voltage and error-correction type. Standard DDR4 is 1.2 V. Both processors are listed as non-ECC, so select ordinary non-ECC desktop DIMMs unless a board manual documents a special compatibility mode.
- Update firmware before a major upgrade when practical. A BIOS update can add processor or memory support, but install only the version intended for the exact board revision and follow the manufacturer’s recovery instructions.
How much RAM and how many modules should I install?
Both processors provide two memory channels. A two-DIMM matched kit lets the board populate one module per channel; this is generally simpler to validate than mixing several unrelated modules.
The processor ceilings are different: Intel lists 64 GB for the i7-7700K and 128 GB for the i7-8700K. Those numbers do not tell you the ideal gaming capacity or guarantee that a particular board accepts it. The motherboard manual determines whether, for example, two 32 GB modules or four 16 GB modules are supported and at what speed.
Avoid combining old and new kits merely to reach a larger total. Mixed kits can have different memory chips, ranks, timings and voltage requirements. Even when the computer starts, the firmware may select a slower setting or require manual stability testing.
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- Turn off the computer, disconnect AC power and ground yourself before opening the case. Consult the board manual for the correct slot pair.
- Press each module straight down until both latches lock. Uneven insertion is a common cause of a no-boot condition.
- Enter the firmware setup on the first boot and confirm that the total capacity and both channels are detected.
- Leave memory settings on the board’s automatic or standard profile for the first stability check. Do not begin by applying an overclocking profile.
- Boot the operating system and verify the reported capacity and speed. A lower-than-advertised speed can be normal when the board has selected a conservative setting.
- If the system is stable, you can evaluate a manufacturer-provided memory profile only if the board and kit documentation support it. Restore default settings if the machine becomes unstable.
What if the computer will not boot after a RAM upgrade?
Start with the simplest physical and configuration checks before blaming the processor.
- Power down and reseat every DIMM; test one module in the slot the manual designates for a single-DIMM start.
- Clear the firmware settings according to the motherboard manual, then retry at default memory settings.
- Confirm that the modules are DDR4 UDIMMs for a DDR4 board, not DDR3L or laptop SO-DIMMs.
- Test modules individually to distinguish a bad DIMM from a bad slot or an incompatible multi-module configuration.
- Check the QVL, board revision and BIOS version. A CPU upgrade can require a board firmware version that an older installation does not have.
- If moving to an i7-8700K, verify that the board is a supported 300-series model; an LGA1151 label alone is insufficient.
Can I reuse the same RAM when upgrading from a 7700K to an 8700K?
You can usually reuse compatible DDR4 UDIMMs if the modules meet the new 300-series board’s requirements. DDR4-2400 is within the Intel-rated memory choices for both processors, but the new board’s QVL, capacity rules and BIOS still decide whether your exact kit works.
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DDR3L used in a 7700K system is not reusable for an 8700K platform. The motherboard must also change in a typical 7700K-to-8700K upgrade because Intel does not support i7-87xx processors on 100- or 200-series chipset boards.
Does faster RAM produce a documented performance gain on these CPUs?
The specifications establish supported data rates, not a universal gaming or application-performance percentage. Actual results depend on the motherboard configuration, memory timings, workload, graphics hardware and software, and no Intel figure in these specifications compares DDR4-2400 with DDR4-2666 on these exact processors.
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Choose a supported, stable configuration first. A higher advertised number is not useful if the board cannot train the DIMM reliably or must operate it at a fallback speed.
Compatibility checklist
- Desktop DDR4 UDIMM selected for either processor.
- DDR4-2400 chosen when one specification must cover both CPUs.
- DDR4-2666 reserved as the Intel-listed speed for the i7-8700K, subject to board support.
- DDR3L considered only for an i7-7700K board explicitly designed for it.
- DDR5 excluded from both platforms.
- Non-ECC, unbuffered modules selected.
- Capacity kept within both the processor limit and the motherboard limit.
- Two-channel slot population and the board QVL checked.
- 100/200-series platform confirmed for an i7-7700K and 300-series platform confirmed for an i7-8700K.
Frequently Asked Questions
Can I install one 8 GB DDR4 module in an i7-7700K system?
A single module can work if the motherboard supports its capacity and the manual identifies a valid single-DIMM slot. It will use one memory channel, so adding a matched second module later may change channel operation and requires following the board’s slot-population guidance.
Will a 32 GB DDR4 module work in an i7-8700K motherboard?
Not necessarily. The processor’s 128 GB ceiling does not certify every DIMM density; the motherboard BIOS, memory-chip organization and QVL determine whether a 32 GB module is recognized and stable.
Do I need to enable XMP for DDR4-2400 to work?
No. DDR4-2400 can run at standard automatic settings when the board supports it. XMP is an optional memory profile, and enabling one can change voltage or timings beyond the board’s default configuration.
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Reseat the DIMMs, test each module separately and confirm that the board supports the installed capacity per slot. A 32-bit operating-system limitation, reserved hardware memory or a firmware compatibility problem can also reduce the usable amount even when the modules are physically present.
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