Arrow Lake: Intel's desktop processors slow down high-end SSDs
Intel's design of the Core Ultra 200S leads to a disadvantage – it slows down PCIe 5.0 SSDs. Latencies are apparently to blame.
We were able to reproduce the problem using a Crucial T705. However, the mainboard and SSD manufacturer are not to blame.
(Image: c't / chh)
With Intel's desktop processors of the Core Ultra 200S (Arrow Lake) series, a phenomenon has remained undiscovered until now: High-end SSDs with a PCI Express 5.0 connection cannot exploit their full speed with Intel CPUs. Up to 14 percent performance is lost.
This affects all processors in this series, from the Core Ultra 5 225F to the Core Ultra 9 285K, and all mainboards with an 800 series chipset. The multi-chip structure of the Arrow Lake CPUs, or how Intel has implemented it, is to blame. The PCIe 5.0 lanes for the M.2 slots are located in a small additional chiplet that Intel calls an I/O extender.
The connection of the I/O extender slows down the interface. The website The SSD Review was the first to notice the problem. In a statement, Intel writes: "Intel can confirm that PCIe lanes 21 through 24 of the Gen 5 root port on Intel Core Ultra 200S series processors may experience increased latencies compared to PCIe lanes 1 through 16 of the Gen 5 root port due to a longer die-to-die data path. However, these variations depend on the workload and capabilities of the PCIe end device."
The interface for the first 16 PCIe 5.0 lanes is located in the larger SoC chiplet next to the integrated graphics unit. These 16 lanes are typically reserved for the graphics card slots. Labeled die shots show the allocation.
Up to 14 percent is lost
The fastest PCIe 5.0 SSDs actually read sequentially at 14 to 14.3 GByte/s. In M.2 slots on Arrow Lake mainboards, however, they only manage up to 12.3 GByte/s. When writing, the sequential transfer rate drops less sharply. We measured 11.8 GByte/s instead of 12.7 GByte/s with a Crucial T705 – tested with a Core Ultra 5 245K on an Asus ROG Maximus Z890 Hero.
| Sequenzielle Transferraten von Crucials T705 | ||
| Plattform | Core Ultra 5 245K + Z890 | Ryzen 7 9800X3D + X870 |
| Lesen M.2-Slot | 12.192 MByte/s | 14.230 MByte/s |
| Schreiben M.2-Slot | 11.812 MByte/s | 12.749 MByte/s |
| Lesen PEG-Adapter | 14.128 MByte/s | unverändert |
| Schreiben PEG-Adapter | 12.366 MByte/s | unverändert |
SSDs reach their full sequential speed with an adapter for the PCIe x16 slot connected to the processor. However, The SSD Review also notes here that the performance drops by a good five percent with random accesses. The 16 lanes from the SoC chiplet are primarily intended for graphics cards. If two cards are used, the lanes are divided into two sets of eight.
Videos by heise
It still needs to be clarified whether slower PCIe 5.0 and 4.0 SSDs will also run more slowly on the current Intel platform. For notebooks, mobile workstations with the Core Ultra 200HX could be affected. The other notebook series use other chips. Meanwhile, there are no problems with AMD: On an Asus Prime X870-P Wifi with Ryzen 7 9800X3D, the Crucial T705 always reached its full speed.
Empfohlener redaktioneller Inhalt
Mit Ihrer Zustimmung wird hier ein externer Preisvergleich (heise Preisvergleich) geladen.
Ich bin damit einverstanden, dass mir externe Inhalte angezeigt werden. Damit können personenbezogene Daten an Drittplattformen (heise Preisvergleich) übermittelt werden. Mehr dazu in unserer Datenschutzerklärung.
(mma)
