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Re: Maximum SD card capacity, what happens if you exceed it?

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In article <3335b7b255.DaveMeUK@my.inbox.com>, Dave Higton wrote:
> No flash drive or flash card is made with an integral power of 2
> capacity.

Well ... yes and no. Almost every flash memory card (the 200GB SanDisk 
one being the only exception of which I am aware) is sold as having a 
power-of-two capacity -- just look at the 16GB, 32GB, 64GB, etc., cards 
on the market. As you say, a little of the capacity is reserved for the 
controller's wear-levelling activities, but the makers don't draw 
attention to that by calling the cards 15GB, 30GB, etc.

PC SSDs with intelligent controllers do generally reserve space to 
assist with their wear-levelling functions, so a 256GB flash chip might 
be used in a nominally 240GB SSD -- SanDisk make one of those, for 
example -- but that's not a 200GB SSD. You don't need to reserve 20% of 
the chip's capacity for wear levelling.

Recently, I've been seeing more SSDs sold with 256GB, 512GB, etc., 
capacities and fewer with 240GB, 48GB, etc., and the newer cards really 
do have larger capacities. I'm not sure whether that's because the wear 
levelling has become cleverer and needs less reserved space to work 
well, or because the makers have started using over-sized flash chips 
so that they can sell the SSDs as having "standard" sizes.

The controllers in SD cards aren't as smart as the controllers in hard 
disk replacement SSDs. They still do wear levelling, but it's not as 
aggressive and doesn't need as much reserved space. About 3% would be 
normal.

So, why do SanDisk sell a 200GB SD card, and what is the actual 
capacity of the flash chips in it? I don't know ...

As far as I can see, though, the 200GB card is an oddity. The *only* 
SanDisk flash memory card available in 200GB (or any non power-of-two) 
capacity is their "Ultra UHS-I" micro-SD card, and that card is also 
available in 256GB capacity. I wonder whether that card is a 4-chip 
design and the 200GB card is actually a 192GB card in which one of the 
chips is faulty? That could be the case if the card is particularly 
hard or expensive to make and SanDisk want to salvage as many of the 
reject cards as possible.

Weird.

-- 
Cheers,
 Daniel.
 

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Maximum SD card capacity, what happens if you exceed it? Chris Green <cl@isbd.net> - 2016-08-17 23:15 +0100
  Re: Maximum SD card capacity, what happens if you exceed it? Ken Blake <Ken@invalid.news.com> - 2016-08-17 15:53 -0700
    Re: Maximum SD card capacity, what happens if you exceed it? crankypuss <undisclosedUserid@gmail.com> - 2016-08-18 08:56 -0600
      Re: Maximum SD card capacity, what happens if you exceed it? Poutnik <poutnik4nntp@gmail.com> - 2016-08-18 19:01 +0200
  Re: Maximum SD card capacity, what happens if you exceed it? AL <noemail@none.com> - 2016-08-17 16:14 -0700
    Re: Maximum SD card capacity, what happens if you exceed it? AL <noemail@none.com> - 2016-08-17 16:31 -0700
  Re: Maximum SD card capacity, what happens if you exceed it? tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-08-17 22:21 -0400
    Re: Maximum SD card capacity, what happens if you exceed it? Poutnik <poutnik4nntp@gmail.com> - 2016-08-18 07:38 +0200
      Re: Maximum SD card capacity, what happens if you exceed it? Chris <ithinkiam@gmail.com> - 2016-08-18 07:22 +0000
  Re: Maximum SD card capacity, what happens if you exceed it? crankypuss <undisclosedUserid@gmail.com> - 2016-08-18 08:55 -0600
  Re: Maximum SD card capacity, what happens if you exceed it? Daniel James <daniel@me.invalid> - 2016-08-19 15:20 +0100
    Re: Maximum SD card capacity, what happens if you exceed it? musika <mUs1Ka@NOSPAMexcite.com> - 2016-08-19 15:36 +0100
      Re: Maximum SD card capacity, what happens if you exceed it? Daniel James <daniel@me.invalid> - 2016-08-20 15:52 +0100
        Re: Maximum SD card capacity, what happens if you exceed it? Dave Higton <dave@davehigton.me.uk> - 2016-08-20 19:15 +0100
          Re: Maximum SD card capacity, what happens if you exceed it? Daniel James <daniel@me.invalid> - 2016-08-27 17:49 +0100
            Re: Maximum SD card capacity, what happens if you exceed it? Dave Higton <dave@davehigton.me.uk> - 2016-08-27 20:40 +0100
              Re: Maximum SD card capacity, what happens if you exceed it? Daniel James <daniel@me.invalid> - 2016-08-28 14:54 +0100
    Re: Maximum SD card capacity, what happens if you exceed it? AL <noemail@none.com> - 2016-08-19 08:11 -0700
    Re: Maximum SD card capacity, what happens if you exceed it? Theo Markettos <theom+news@chiark.greenend.org.uk> - 2016-08-20 23:32 +0100
      Re: Maximum SD card capacity, what happens if you exceed it? Chris Green <cl@isbd.net> - 2016-08-21 10:28 +0100
  Re: Maximum SD card capacity, what happens if you exceed it? Micky <NONONObobbyburns1111@gmail.com> - 2016-08-20 07:02 -0400
    Re: Maximum SD card capacity, what happens if you exceed it? Micky <NONONObobbyburns1111@gmail.com> - 2016-08-20 07:12 -0400
    Re: Maximum SD card capacity, what happens if you exceed it? Nigel Wade <nmw@local.domain> - 2016-08-22 09:55 +0100
      Re: Maximum SD card capacity, what happens if you exceed it? Micky <NONONObobbyburns1111@gmail.com> - 2016-08-22 11:15 -0400

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