Joe rock wrote:
Il 14/12/2020 17:01, Paul ha scritto:
Is it true ?
Regards
I'll pretend to be the plant manager for a moment.
"Why don't we put the microSD product, inside an SD
package ? And kill two birds with one stone."
And, it gets worse. Here, we discover they used a carrier
inside an SD and placed a microSD in it.
https://www.reddit.com/r/mildlyinteresting/comments/2k6qxh/just_opened_up_my_broken_sd_card_to_find_it/
Now, how is that for a cheeky design :-)
Ok, surely you are right , my question was relative to the majoer space
in the SD than in microSD , so it could use a better controller.
But they are the same, microSD embedded in SD , so they are egual.
I would like use SD or microSD as storage of OS , but they are slow in
r/w operations.
Paul
Joe Rock
But there are standards versions, and designs,
that go faster than the Class 10 you're holding in your hand.
The hardest part for the SD user, is buying computer devices
with the right version of SD interface on them. Lots of
computers have the "bad" SD on them. Preventing the
better SD cards from being used.
https://en.wikipedia.org/wiki/SD_card
"Standard: 12.5 MB/s
High-speed: 25 MB/s
UHS-I: 50 MB/s or 104 MB/s
UHS-II: 156 MB/s full-duplex, or 312 MB/s half-duplex
UHS-III: 312 MB/s full-duplex, or 624 MB/s full-duplex
Express: ~985 MB/s full-duplex
"
UHS-I , at around 95MB/sec, is the most practical. You
can actually find those. The Express one, that standard
is too new for much product to have appeared yet. It uses
a PCI Express lane.
The "Express" one, mimics NVMe, in that the UEFI BIOS needs
a firmware module to read from the NVMe. Even if you fitted
some sort of hardware card as an adapter, the BIOS is unlikely
to want to touch it, on an older computer.
Then there's the issue of whether an OS really wants to boot
from SD. An obvious example is Raspberry PI and Linux, which
seem to be happy to use SD. The RPi 4 recently got the ability
to boot from SATA (using a USB3 to SATA adapter?), so it now
has ways to get around the SD interface limitations.
I don't think Windows would boot from SD. They managed to
get Windows to boot from a USB stick, with Windows To Go.
But that's been deprecated on Windows 10 just recently
(within the last year).
And we don't really know how good the wear leveling is on SD.
The same applies to USB keys. I have a couple dead USB keys
here, that received light usage, and they seem to have
failed on me without too much effort (the sticks had Linux
with persistent store loaded). I don't really know
whether SD dies like that too or not. I don't have any projects
here, requiring OS booting from SD, and the only SD card I own
is still in fine shape.
The largest SD seems to be 512GB. They might be offered for
sale. There are supposed to be some higher capacity than that,
but they're not available for sale from any manufacturer
sales page. Which suggests they're not really ready to be
used by customers. But 512GB is a pretty decent size. Enough
to boot just about any SD-compatible OS, with room left over.
Paul
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