Is your RAM at its rated speed? XMP, EXPO and dual channel

You bought a DDR5-6000 kit and Task Manager reports a lower number. Or CPU-Z shows 3000 MHz and the memory seems to run at half speed. Only the first is a problem. Memory has two settings that can be quietly wrong — its speed, and whether both channels are in use — and one reading that only looks wrong.

Why new memory starts below the number on the box

On a kit sold with XMP or EXPO, the rated speed can be a profile stored on the modules rather than the speed they start at. A new kit starts on standard settings defined by JEDEC, the industry standards body. Intel says XMP modules "will first boot with the default JEDEC settings", which "ensures the first boot is successful even if the system does not support overclocking" (Intel). The faster settings stay unused until you tell the BIOS to apply them.

• XMP is Intel's format — "a type of memory overclocking", in Intel's words.
• EXPO is AMD's, described by AMD as "user-friendly memory overclocking" for Ryzen processors on socket AM5 (AMD).

Board makers rename them: ASUS offers XMP I, EXPO I or DOCP depending on the kit and the platform (ASUS), and the manual for MSI's MPG B550 Gaming Plus says A-XMP.

Because both are overclocking, a kit's rating can exceed what the processor is specified for. AMD lists DDR5-5200 as the maximum for a Ryzen 9 7950X with two modules, so a DDR5-6000 kit on its EXPO profile runs outside AMD's published specification. Intel's figure is DDR5 5600 MT/s for the Core i9-14900K and DDR5 6400 MT/s for the Core Ultra 9 285K.

Check the speed you are actually running

Press Ctrl+Shift+Esc and go to Task Manager > Performance > Memory. Two lines matter:

• Speed is the transfer rate. With the profile active it should match the rating; ASUS points to this screen for checking a profile.
• Slots used, shown as for example 2 of 4, counts the modules Windows sees.

If Speed is lower than the rating, the rated profile is not in effect.

MT/s versus MHz. DDR memory transfers data on both the rising and the falling edge of each clock cycle, which is why MT/s (megatransfers per second) is the accurate unit for its speed (Kingston). Some board manuals still write the transfer rate as MHz — MSI's lists DDR4 speeds such as "3200 MHz" — and mean the same figure.

Why CPU-Z shows half. CPU-Z reports the memory clock rather than the transfer rate, so it shows about half the rating. In Corsair's own example, CPU-Z shows a DDR5-6000 kit as a 3,000 MHz memory bus. That is correct, not a fault; double it before you compare.

Turn the profile on

1. Restart and press Del repeatedly before Windows starts loading. Some boards use F2 or another key.
2. On an ASUS board, press F7 for Advanced Mode, open Ai Tweaker and set Ai Overclock Tuner to XMP I for an XMP kit on an Intel board, or EXPO I for an EXPO kit on an AM5 board. When kit and platform do not match — an XMP kit on AM5, or an EXPO kit on an Intel 600-series or newer board — ASUS offers DOCP instead. On other boards, follow the manual; Corsair notes the labels differ enough "to make things tricky".
3. If the kit has several profiles, start with Profile 1.
4. Save and exit (F10 on ASUS), then check Speed in Task Manager again.

If the PC no longer starts, clear the CMOS — ASUS's answer for a failed profile — to return the BIOS to defaults. A BIOS update is also on both Corsair's and MemTest86's lists.

A profile that boots is not yet a stable one

Memory faults do not announce themselves as memory faults. PassMark, which makes MemTest86, lists "Corrupted data, crashes and unexplained behaviour" and calls the symptoms "often random and hard to pin down" (MemTest86). Microsoft lists memory among the causes of two stop errors, WHEA_UNCORRECTABLE_ERROR and VIDEO_TDR_FAILURE. If crashes started after you enabled a profile, take the profile out first; MemTest86's own list of fixes includes "Set default or conservative RAM timings / Disable XMP".

Then test, in this order:

1. Windows Memory Diagnostic. In the Control Panel search box, type Memory and select Diagnose your computer's memory problems. After the test, find the MemoryDiagnostics-Results entry in Event Viewer's System log (Microsoft).
2. MemTest86 boots from a USB flash drive and tests outside Windows. PassMark says a single pass "is sufficient to catch consistent errors" but advises testing "for a longer period" when errors are intermittent. Its example times: 15 minutes for one pass, 120 minutes for the default four.

Read the result both ways. An error does not prove a bad stick: the test also exercises the CPU, its caches and the motherboard. A clean pass does not prove the profile stable in your game either; PassMark notes some errors are temperature-sensitive.

Dual channel: two sticks in the right two slots

AMD and Intel list two memory channels for every processor named above, and Kingston describes dual-channel systems as built around "a pair of identical memory modules". With a single stick, or both sticks on one channel, only one channel is in use.

Four-slot boards are sometimes labelled A1, A2, B1 and B2, the letter being the channel. Corsair's general advice for two sticks is A2 and B2; MSI's manual says "Always insert memory modules in the DIMMA2 slot first" and pairs it with B2. Your own board's manual is the authority.

To confirm:

• Task Manager's Slots used should count both modules.
• CPU-Z reports the channel mode. In CPU-Z's own reports, a DDR4 pair in the right slots reads "Dual Channel (128 bit)".
• DDR5 reads differently. Kingston explains that DDR5 "splits the memory module into two independent 32-bit addressable subchannels", while each module stays 64 bits wide. CPU-Z can count those sub-channels as channels: its report for a two-module DDR5 system reads "Quad Channel (128 bit)". That is still dual channel. Check the total width — two channels of 64 bits make 128.

Four sticks: more capacity, lower supported speed

Filling all four slots puts two modules on each channel, and the supported speed drops. AMD's figures for the Ryzen 9 7950X are DDR5-5200 with two modules and DDR5-3600 with four; for the Ryzen 9 9950X, DDR5-5600 and DDR5-3600. Kingston explains that, when overclocking, modules in the second bank of sockets place "a heavy burden" on the processor, "specifically at high speeds and low latencies". Four modules that will not hold the profile do not, by that alone, prove a stick faulty.

If you need four, buy them as one kit. ASUS asks for kits of two or four to be used as sold — "do not mix" — and points to its memory support list, the QVL. AMD keeps a list of kits "tested across systems to run at rated speed and latency". Kingston adds that a pair bought later can carry different chips "even if it's the same specification or part number".

What this does not promise

The profile changes how fast the memory runs; what that does in your game is not something a guide can promise. Measure it: same scene, before and after, several runs each. w0a's Benchmark page measures frame times while you play your own game, and the 1% low is the number to compare (Reading the benchmark).

What does not help:

• "Fixing" CPU-Z's half figure: it is the clock, and correct.
• Keeping a profile that crashes, or a mismatched second kit, because it is mostly fine. PassMark warns that marginal memory "can result in data loss and even disk corruption".

Related

• PC restarts or shuts down while gaming
• Why did my game crash?
• Reading the benchmark
• Task Manager for gamers