2026-01-15
Why CPU-Z DRAM frequency looks "half" of DDR4-3600
You just installed a brand-new DDR4-3600 memory kit, fired up CPU-Z, opened the Memory tab and saw 1800 MHz next to "DRAM Frequency." Panic sets in — did you get scammed? Is something broken? Relax. Your RAM is almost certainly running exactly as intended. The number CPU-Z displays is the real clock speed, not the marketing speed printed on the box. This article explains why the two numbers differ, how to read the Memory tab correctly, and what to do if the frequency genuinely is too low.
How DDR works
DDR stands for Double Data Rate. Unlike older SDR (Single Data Rate) memory, DDR transfers data on both the rising and falling edges of the clock signal. That means every clock cycle produces two data transfers instead of one. The result is an effective data rate that is exactly double the base clock frequency.
When a manufacturer labels a kit "DDR4-3600," the 3600 refers to 3600 mega-transfers per second (MT/s) — the effective rate after doubling. The actual oscillator inside the memory module runs at 1800 MHz. CPU-Z reports this real oscillator frequency, which is why the number appears to be "half" of what you expected.
Tip: To get the marketed speed from the CPU-Z reading, simply multiply the displayed DRAM Frequency by 2. If CPU-Z shows 1800 MHz, your effective speed is 3600 MT/s — exactly DDR4-3600.
DRAM frequency to DDR speed reference table
Use the table below as a quick cross-reference when reading CPU-Z values.
| DRAM Frequency (CPU-Z) | Effective Speed | Marketing Name |
|---|---|---|
| 1066 MHz | 2133 MT/s | DDR4-2133 |
| 1200 MHz | 2400 MT/s | DDR4-2400 |
| 1333 MHz | 2666 MT/s | DDR4-2666 |
| 1600 MHz | 3200 MT/s | DDR4-3200 |
| 1800 MHz | 3600 MT/s | DDR4-3600 |
| 2000 MHz | 4000 MT/s | DDR4-4000 |
| 2400 MHz | 4800 MT/s | DDR5-4800 |
| 2800 MHz | 5600 MT/s | DDR5-5600 |
| 3200 MHz | 6400 MT/s | DDR5-6400 |
| 3600 MHz | 7200 MT/s | DDR5-7200 |
JEDEC vs XMP/EXPO
Every DDR module ships with a set of JEDEC timings burned into its SPD (Serial Presence Detect) chip. These are conservative, guaranteed-stable profiles that the BIOS loads by default. For DDR4, the highest standard JEDEC speed is 3200 MT/s; for DDR5, it is 5600 MT/s. If your kit is rated higher than that, the extra speed comes from an overclocking profile:
- XMP (Extreme Memory Profile) — Intel's specification, now in version 3.0 for DDR5.
- EXPO (Extended Profiles for Overclocking) — AMD's equivalent for Ryzen platforms.
Until you activate one of these profiles in your BIOS, the motherboard will default to JEDEC speeds. That means your DDR4-3600 kit might show only 1066 MHz (DDR4-2133) in CPU-Z — far below what you paid for. This is not a defect; it is simply the safe default. The SPD tab in CPU-Z lists every profile the module exposes, so you can verify which XMP or EXPO profiles are available before rebooting into BIOS.
How to enable XMP or EXPO in BIOS
- Restart your PC and press the BIOS key during POST (usually DEL or F2).
- Navigate to the memory or overclocking section. The exact location varies by motherboard brand — ASUS calls it "AI Tweaker," MSI uses "OC," Gigabyte labels it "Tweaker."
- Find the XMP or EXPO toggle and select Profile 1 (or whichever profile matches your desired speed).
- Save and exit (usually F10). The system will reboot with the new memory timings.
- Open CPU-Z again and confirm the DRAM Frequency now reflects the correct base clock (e.g., 1800 MHz for DDR4-3600).
Common mistakes when reading memory speed
- Confusing MHz with MT/s. CPU-Z shows the true clock in MHz. The box speed is in MT/s (mega-transfers per second). Multiply by 2 to convert.
- Forgetting to enable XMP/EXPO. This is the number-one reason people see a frequency far below the rated speed. Always check your BIOS after installing new RAM.
- Mixing kit speeds. If you install two kits with different speed ratings, the motherboard will usually downclock all sticks to the slowest common speed. CPU-Z will reflect this lower frequency.
- Single vs dual channel. The Memory tab also shows channel mode. Running in single-channel halves your bandwidth even if the frequency is correct. Make sure sticks are in the right slots (usually A2 and B2).
- Reading the wrong tab. The SPD tab shows what the module supports; the Memory tab shows what is currently active. Always check the Memory tab for real-time frequency.
Tip: DDR5 modules include an on-die voltage regulator (PMIC), so their SPD data is structured differently from DDR4. CPU-Z versions 2.0 and later fully decode DDR5 SPD, including XMP 3.0 and EXPO profiles. If you are running DDR5, make sure you are using an up-to-date version of CPU-Z for accurate readings.
Summary
The "half speed" reading in CPU-Z is completely normal and expected. DDR memory has always worked this way — the base clock is half the effective transfer rate. If the frequency is lower than half your rated speed, enable XMP or EXPO in BIOS. If it matches half, everything is working perfectly.
For a complete walkthrough of every CPU-Z tab, visit the CPU-Z guide. You can also browse the glossary for definitions of terms like JEDEC, XMP, SPD, and more.