So, naturally, when I realized that there was a toggle in the system BIOS that could effectively cut the waiting time in half, I leaped at the opportunity.
Here's everything you need to know about the root cause, which happens to be memory training.
Memory training is generally the reason whyBefore we get to the "fix", it's prudent to understand what the "issue" primarily relates to.
Memory training is a calibration routine your motherboard runs during Power-On Self-Test (POST), before your OS loads.
MCR can speed up boot times, but it isn't foolproofBased on my own experiments, MCR certainly makes the boot process a little faster if done correctly by skipping memory training.
Two years ago, when I built my PC with a Ryzen 5 7600X, DDR5 memory, and a lightning-fast PCIe Gen 4 NVMe SSD, I certainly didn't expect boot times to ever be an issue. And yet, every time I hit the power button, I'm left staring at a black screen for the better part of a minute before I'm greeted by the familiar Windows login screen.
It's a strange problem to have. It has never been serious enough for me to drop everything and put on my troubleshooting hat, but over time, it has become annoying enough to feel like an issue. So, naturally, when I realized that there was a toggle in the system BIOS that could effectively cut the waiting time in half, I leaped at the opportunity. Here's everything you need to know about the root cause, which happens to be memory training.
Why do DDR5 systems take so long to boot?
Memory training is generally the reason why
Before we get to the "fix", it's prudent to understand what the "issue" primarily relates to. Memory training is a calibration routine your motherboard runs during Power-On Self-Test (POST), before your OS loads. It tunes the connection between the CPU's memory controller and your RAM by testing different voltages, sub-timings, signal strengths, and data alignments until it finds a stable combination.
Now, there's a special reason as to why the issue exists on DDR5 platforms in particular. Simply put, faster RAM is harder to run reliably, and since most users run their memory at EXPO profiles, it becomes even more relevant. As a matter of fact, a system that's using the preceding DDR4 standard can generally boot faster than one using the DDR5 standard, mainly because DDR5 operates at much higher transfer rates while also introducing a more complex memory architecture.
DDR5 has tighter electrical margins, on-die power management, and independent 32-bit sub-channels, which all give the memory controller more parameters to negotiate during training, and as such, enabling an EXPO profile means that the motherboard has even more work to do. Fortunately, most of the cost lands on the first POST after a build, a BIOS update, a CMOS reset, or a kit swap, but it can still feel pretty long unless you head into the BIOS and make a change.
What is Memory Context Restore?
And how does it make boot times faster?
Close
Memory Context Restore (MCR) happens to be the one setting that can potentially cut down memory training time on DDR5 systems, but before you head into the BIOS/UEFI, it's worth understanding what it does and how it does it.
Originally, AMD introduced this through an AGESA update after the Ryzen 7000 series launch, and its only job is to stop the motherboard from performing recurring memory training loops on every startup. The way it works is such that, after a successful memory training pass, MCR lets the system retain the configuration, including the timings, voltages, and controller settings that worked as intended. On subsequent boots, the motherboard simply reloads the last-known stable state instead of running the entire training process from scratch.
This is precisely where the boot-time savings come from. If the system has identified the stable parameters from the last few runs, it can save the time spent on the re-training process. It's important to note, though, that enabling or disabling MCR has not been known to have any impact on memory performance. It doesn't increase bandwidth, reduce latency, or make your RAM faster or slower in the process, and the only known effect has been on the time taken for the system to boot from a cold start.
There are some things worth keeping in mind while using MCR
Enabling MCR is only half the job, and on rare occasions, not worth it
MCR isn't always a one-click fix, particularly if you have a Ryzen 7000 series chip. The other setting worth checking is Power Down Enable, which puts the memory into a low-power state when it's idle. On some AM5 boards, enabling MCR without it has led to black screens, failed restarts, or the occasional BSoD. Users on computing and overclocking forums have remarked that turning Power Down Enable alongside MCR tends to resolve these issues.
The other thing to remember is that the entire premise of MCR is based on the assumption that your last-known memory configuration is stable. If you change your DIMM sticks, alter your timings, tweak your EXPO settings, or reset the BIOS, your RAM will need to undergo memory training, and therefore, it's important to disable MCR before making those changes. If you frequently tweak those settings and are at risk of forgetting to disable MCR, you're probably better off spending an extra minute for your PC to boot.
MCR can speed up boot times, but it isn't foolproof
Based on my own experiments, MCR certainly makes the boot process a little faster if done correctly by skipping memory training. It's also worth noting that the changes don't translate uniformly across all system configurations using motherboards from different manufacturers. If, however, you've experimented with MCR before and that has led you to a boot loop or resulted in system instability, remember that a CMOS reset will force fresh training, and that usually spells the end of the issue as it resets your BIOS settings back to their original defaults.
