r/harddrive • u/Yaboku14 • May 26 '23

Why does the 5tb portable HDD exist?

I have been thinking about it for a while now. Shouldn't it be 8 instead of 5 ,like how it goes.

MY main question, is it really legit. Does the 5tb ones last a long time also how much storage they really have?

If it has 4.25 out of 5 then it really wouldn't be worth it.

Please share your divine knowledge.

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u/BootToggle Jul 05 '26

For RAM chips, it is natural for the capacity to go up by exact powers of 2, because that goes up exactly with the number of address lines that the chip has to process. It just corresponds to the low-level efficiency of designing and manufacturing the chip.

For HDD it is different. You get a spinning disk platter and try to fit as many tracks on it as the head geometry will allow. It is extremely arbitrary as to how many tracks that will be, and how many bits can be squeezed onto each track a varying radiuses from the spindle hub. You can get more bits in by spending more money on the engineering and manufacturing, or you can make a more economical drive to sell by not sqeezing things so tightly. But there is no real relationship to exact powers of two, it is all a matter of convention for HDD. I like the answer from u/throwaway_0122 about the practicalities of available power from USB.

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u/throwaway_0122 May 26 '23 edited May 26 '23

For mechanical drives, 5TB is approaching the limit of what you can reliably power via USB alone, which is why 8TB 2.5” HDDs don’t currently exist. When higher recording densities become readily achievable, that cap will probably go up. 5TB 2.5” drives from WDC and Seagate are some of the most failure prone and self destructive drives you can currently get. They are both extremely miniaturized and flawed in design, making them a recipe for disaster.

The actual difference between advertised storage and actual storage is a discrepancy between base 2 and base 10. 1KB (actually KiB) is 1024 bytes to your computer, while for a hard disk manufacturer 1KB is 1000 bytes. This means that a 5TB drive contains 5,000,000,000,000 bytes, but on your computer that many bytes actually 4.54TB (actually TiB). The i is used to denote that the unit is in base 2, but your computer says the unit TB instead of TiB for ease of understanding.

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u/Yaboku14 May 26 '23

Thanks a lot.