Hacker News Reader

Comment by jachee | Hacker News Reader

The entire reason "storage vendors prefer" 1000-based kilobytes is so that they could misrepresent and over-market their storage capacities, getting that 24-bytes per-kb of expectation-vs-reality profit.

It's the same reason—for pure marketing purposes—that screens are measured diagonally.

View on HN

Not sure about that, SSDs historically have followed base-2 sizes (think of it as a legacy from their memory-based origins). What does happen in SSDs is that you have overprovisioned models that hide a few % of their total size, so instead of a 128GB SSD you get a 120GB one, with 8GB "hidden" from you that the SSD uses to handle wear leveling and garbage collection algorithms to keep it performing nicely for a longer period of time.

Sounds like an urban legend. How likely is it that the optimal amount over-provisioning just so happens to match the gap between power-ten and power-two size conventions?

It doesn't, but it's convenient.

It doesn't, there's no singular optimal amount of over-provisioning. And that would make no sense, you'd have 28% over-provisioning for a 100/128GB drive, vs 6% over-provisioning for a 500/512GB drive, vs. 1.2% over-provisioning for a 1000/1024GB drive.

It's easy to find some that are marketed as 500GB and have 500x10^9 bytes [0]. But all the NVMe's that I can find that are marketed as 512GB have 512x10^9 bytes[1], neither 500x10^9 bytes nor 2^39 bytes. I cannot find any that are labeled "1TB" and actually have 1 Tebibyte. Even "960GB" enterprise SSD's are measured in base-10 gigabytes[2].

0: https://download.semiconductor.samsung.com/resources/data-sh...

1: https://download.semiconductor.samsung.com/resources/data-sh...

2: https://image.semiconductor.samsung.com/resources/data-sheet...

(Why are these all Samsung? Because I couldn't find any other datasheets that explicitly call out how they define a GB/TB)

More recently you'd have, say, a 512GB SSD with 512GiB of flash so for usable space they're using the same base 10 units as hard disks. And yes, the difference in units happens to be enough overprovisioning for adequate performance.

Reply on news.ycombinator.com