What is the probability of a bit error occuring when reading/writing from/to the latest memory technologies (ssd, hdd, ram) in modern computers? If the same terminology is used in this context as in networking/communication systems, then my question can be rephrased as:

What is the bit error rate(BER) when accessing memory either to read/write in modern computers?

As a follow up question, how do computers deal with such bit errors?

  • \$\begingroup\$ Pull up any harddrive spec sheet and it should list it. \$\endgroup\$
    – DKNguyen
    May 1, 2020 at 20:12
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    \$\begingroup\$ Fairly high. Memory modules (SIMMs,DIMMs) used to have redundant bits for parity and later, error correction. Most commodity ones don't any more, to save a couple bucks, and commodity motherboards don't always support them anyway. If this concerns you, look at high end mobos and ECC memories for servers. They cost extra because it's a niche nowadays. \$\endgroup\$
    – user16324
    May 1, 2020 at 20:19
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    \$\begingroup\$ High enough that any machine used for medical purposes has redundant ECC memory raid hard drives. \$\endgroup\$
    – MadHatter
    May 1, 2020 at 20:21
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    \$\begingroup\$ @MadHatter ECC RAM is what I know; hard drives, not only in RAIDs employ heavy ECC since... I'd guess the mid-90s? So, that's pretty standard. \$\endgroup\$ May 1, 2020 at 20:50
  • \$\begingroup\$ @MarcusMüller You are correct, although I should elaborate that old RAID styles like 5, are no longer used due to the statistical almost guarantee that you'll have a bit error on reconstructing a single hard drive loss. \$\endgroup\$
    – MadHatter
    May 1, 2020 at 22:33

2 Answers 2


Computers handle this by either using software that's designed to blue screen in a controlled manner when critical data structures are corrupted, or by using ECC memory, which stores data with some redundancy to allow a single bit error to be corrected and a double-bit error to be detected with no recourse other than a hard shutdown.

There is some literature analyzing the actual numbers in the context of datacenters. One study tracks the number of dectected-and-corrected errors, showing that, at scale, 2% of machines encountered a recoverable (typically single-bit) ECC fault, while a tiny number encountered unrecoverable (double-bit) faults.

Google tests, shown on slide 11 of this slide deck, reported that 32% of machines would report a correctable per year, while around 1.3% reported uncorrectable errors.

However, it is almost certainly incorrect to consider these bit errors as a randomly-distributed error rate (like you would for an AWGN communication channel). Because DRAM may experience manufacturing imperfections, in practice 20% of servers contribute 90% of the errors, and errors are also likely clustered in time. Google reports strong clustering and age-dependence for their correctable errors, while uncorrectable errors have anomalous behavior (Google HW ops will pull RAM for replacement as soon as an uncorrectable rror arises, according to the paper).

This makes it difficult to compute a meaningful bit error rate that could be expected of any one random computer. There are also other issues with extrapolating these values, since enterprise customers with ECC RAM are going to have very different supply chains, parts, and workloads than home computers. Furthermore, if ECC RAM is made with a different grade of chips than non-ECC ram, then there will be a systematic bias because most of these large-scale studies come from ECC-RAM-based datacenter fleets.


Notice how computers tend to fail, as the bypass capacitors age, because of higher and higher ripple voltages.

Keep that computer COOL, if you want reliable computing.

  • 2
    \$\begingroup\$ Whilst this may be correct advice, it doesn't answer the question as stated, and isn't useful to other readers who may come across this question by searching for a query similar to its title. \$\endgroup\$
    – nanofarad
    May 2, 2020 at 1:40
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    \$\begingroup\$ Also just keeping a computer cool does not necessarily mean it will work better. \$\endgroup\$
    – MadHatter
    May 2, 2020 at 13:23

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