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I noticed this in general: its faster to copy a large file from my computer to my USB than it is to overwrite it. For example, I have a file a.txt thats 10 gb. If my USB is blank and I copy my file to the USB, its pretty quick. However, if my USB already had an outdated version of a.txt and I want to put the new version on it by copying the new one from my computer and pasting it onto my USB, it overwrites the a.txt file. Why does that take longer to overwrite than if my USB was blank? Does it have to do with the number of calls to read/write?

  • You're talking about a USB flash drive, correct? – David Schwartz Mar 18 '14 at 8:57
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Erasing is much slower than writing. Erasing followed by writing, slower still.

  • Can't see in what situation erasing is slower. Even zeroing shouldn't take longer that just writing the same data. Do you have any sources to support that? – EliadTech Mar 18 '14 at 8:28
  • Umm, why do you think TRIM exists?! It's precisely because erasing is slower than writing. Or see this which says, "Because erase cycles are slow, ...". Zeroing is as fast as writing, but once a block is zeroed, it has to be erased to contain anything else. – David Schwartz Mar 18 '14 at 8:56
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    Correct me if I'm wrong but SSD and HDD are far different in operations. SSDs need TRIM because they can't determine which data is free(transistors still holds charge unless manually uncharged). In a delete on an HDD, it is simply deleting a pointer to data allowing that region on the disk to be overwritten which is very quick. This is why Undelete works. On an SSD, it does take longer to free up existing data since it has to actually reset it.See tuaw.com/2011/03/27/keeping-ssds-in-trim-doing-the-math – Jeff F. Mar 19 '14 at 17:33
  • @JeffF. You are correct. That's another way of saying the same thing I'm saying. – David Schwartz Mar 20 '14 at 18:10
  • @David Finally got to the articles you linked to. Though not fully understood (electronics isn't my strong side), I got the general idea. – EliadTech Apr 15 '14 at 21:46
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To copy is a matter, where RAM is involved and where datas are only read. This means - in case of an hard-disk like the EIDE - harddisks with seperated heads for to read and for to write - only the heads for to read are used.

But if you overwrite datas then both heads are used - and the harddisk is working in full progress. Namely with reading and writing ... this lasts "longer" (but is done with enourmous speed !).

Is this question related to ssd - disks or to those SATA hard-drives, who were built before ssd came up ?!

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