Why don’t PCs use error correcting RAM? “Because Intel,” says Linus

Enlarge / We have been having fun with a kinder, gentler Linus Torvalds for the previous couple of years… however that does not imply he stopped having opinions.

This Monday, Linux kernel creator Linus Torvalds went on a pissed off rant concerning the lack of Error Correcting Checksum (ECC) RAM in shopper PCs and laptops.

… the misguided and arse-backwards coverage of “customers do not want ECC”, [made] the marketplace for ECC reminiscence go away.

The arguments towards ECC have been at all times full and utter rubbish. Now even the reminiscence producers are beginning to do ECC internally as a result of they lastly owned as much as the truth that they completely need to.

In the event you’re not acquainted with ECC RAM, it is in all probability since you do not construct or spec devoted servers utilizing server-grade CPUs and motherboards—which, sadly, is about the one place you really discover ECC. In a nutshell, ECC RAM features a tiny quantity of additional reminiscence used for detection and correction of errors.

Reminiscence errors and chance

In most trendy implementations, this implies for each 64-bit word saved in RAM, there are eight checking bits. A single bit error—a 0 flipped to 1, or a 1 flipped to 0—will be each detected and corrected robotically. Two bits flipped in the identical phrase will be detected however not corrected. Three or extra bits flipped in the identical phrase will in all probability be detected, however detection shouldn’t be assured.

Bit flips can occur for a lot of causes, starting with cosmic-ray impression or easy {hardware} failure. A big-scale study of Google servers discovered that roughly 32 p.c of all servers (and eight p.c of all DIMMs) in Google’s fleet expertise at the least one reminiscence error per yr. However the overwhelming majority of those are single-bit errors—and since Google is utilizing server CPUs and ECC RAM, this implies the machines in query hold proper on trucking.

In shopper machines, even these single-bit errors—that are over 40 instances extra more likely to happen than multiple-bit errors, in response to Google’s knowledge—go undetected and might introduce instability into programs and corruption into knowledge.

Bit flips aren’t at all times unintended

Not each RAM error is the results of a {hardware} failure or unintentional EMF downside. Lately, researchers have developed more and more sensible physics-based facet channel assaults, utilizing managed, fast bit flips in areas of RAM accessible to at least one utility to infer or modify the values of knowledge in adjoining areas of RAM they should not be capable to.

Though ECC RAM cannot mitigate RAMBleed-style assaults that deduce the values of adjoining reminiscence, it might probably usually cease Rowhammer assaults—during which quickly flipping bits in a single space of RAM trigger bits in an adjoining space to vary.

Even when ECC cannot actively stop a Rowhammer assault from having an impression on the system—for instance, when it flips a number of bits in a single phrase—it might probably at the least alert the system of the issue and, normally, stop the Rowhammer assault from doing something aside from inflicting downtime. (Most ECC programs are configured to halt the complete machine if an uncorrectable error is detected.)

Torvalds blames Intel

And the reminiscence producers declare it is due to economics and decrease energy. And they’re mendacity bastards—let me as soon as once more level to row-hammer about how these issues have existed for a number of generations already, however these f*ckers fortunately bought damaged {hardware} to customers and claimed it was an “assault,” when it at all times was “we’re reducing corners.”

What number of instances has a row-hammer like bit-flip occurred simply by pure dangerous luck on actual non-attack masses? We’ll by no means know. As a result of Intel was pushing shit to customers.

Torvalds takes the daring place that the dearth of ECC RAM in shopper expertise is Intel’s fault because of the firm’s coverage of synthetic market segmentation. Intel has a vested curiosity in pushing deeper-pocketed companies towards its costlier—and worthwhile—server-grade CPUs quite than letting these entities successfully use the essentially lower-margin shopper elements.

Eradicating assist for ECC RAM from CPUs that are not focused immediately on the server world is likely one of the methods Intel has stored these markets strongly segmented. Torvalds’ argument right here is that Intel’s refusal to assist ECC RAM in its consumer-targeted elements—together with its de facto near-monopoly in that house—is the actual cause that ECC is sort of unavailable outdoors the server house.

The same old argument round why ECC is not current in shopper tech revolves round value, however we suspect Torvalds has the best of it right here. Regardless of ECC RAM being primarily a hard-to-find specialty half, it sometimes solely prices about 20 p.c extra per DIMM than non-ECC does at retail. The actual downside is that with out motherboards and CPUs which assist it, it will not do you any good.

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