| Author |
Message |
Craig
Guest
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 Posted:
Tue Jan 04, 2005 5:05 am Post subject:
Addressong Secure Digital (SD) > 16MB |
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I was wondering if someone could explain how one accesses beyond 16MB
on an SD card if the CMD17 format that reads a block of data contains
only a 32-bit byte address? It seems that would restrict one to only
the first 16MB of data which leaves me at a loss of how to access all
the data contained on a 32MB, 64MB, etc. SD card.
Thanks,
Craig |
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Richard H.
Guest
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| Posted:
Tue Jan 04, 2005 7:57 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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Craig wrote:
| Quote: |
I was wondering if someone could explain how one
accesses beyond 16MB on an SD card if the CMD17
format that reads a block of data contains only a
32-bit byte address? It seems that would restrict
one to only the first 16MB of data which leaves me
at a loss of how to access all the data contained
on a 32MB, 64MB, etc. SD card.
|
Um, doesn't 32 bits = 4,294,967,295 (4GB) of addressing? Or maybe SD
cards use different math... (24 bits = 16MB)
But it does raise a good question - I recall seeing a 2GB card listed
somewhere, and 4GB+ can't be too far behind.
(As an interesting aside, casual Christmastime testing shows that the
cheaper Lexar 1GB SD cards sold by Fry's / Outpost.com write 2x faster
than the "high-performance" SanDisk "Ultra" cards that cost 50% more.)
Richard |
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Craig
Guest
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| Posted:
Thu Jan 06, 2005 3:15 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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| Quote: | Um, doesn't 32 bits = 4,294,967,295 (4GB) of addressing? Or maybe
SD cards use different math... (24 bits = 16MB)
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Ok, I really haven't used Usenet in about a decade and now in both of
my first two posts I look like an idiot. I can't even imagine what
line of reasoning I was using when I stated that 32 bits couldn't
address more than 16MB. Thanks for whacking me upside the head.
| Quote: | But it does raise a good question - I recall seeing a 2GB card
listed somewhere, and 4GB+ can't be too far behind.
|
True. I'll bet when memory capacities of SD Cards are ready to exceed
4GB that they'll probably add a new command to the SD command set to
allow accessing the additional memory. Systems that don't support that
command will only be able to see the first 4GB of the SD card.
What I don't understand is why a digital camera I bought (Canon
PowerShot SD100) says in its manual that only cards up to 256MB should
be used. I haven't tried using a larger card with the camera but I
can't really think what reason there would be for the camera being able
to use 256MB cards but not 512MB or 1GB.
Thanks again for giving me a clue.
Regards,
Craig |
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Tim Wescott
Guest
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| Posted:
Thu Jan 06, 2005 4:21 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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Craig wrote:
| Quote: | Um, doesn't 32 bits = 4,294,967,295 (4GB) of addressing? Or maybe
SD cards use different math... (24 bits = 16MB)
Ok, I really haven't used Usenet in about a decade and now in both of
my first two posts I look like an idiot. I can't even imagine what
line of reasoning I was using when I stated that 32 bits couldn't
address more than 16MB. Thanks for whacking me upside the head.
But it does raise a good question - I recall seeing a 2GB card
listed somewhere, and 4GB+ can't be too far behind.
True. I'll bet when memory capacities of SD Cards are ready to exceed
4GB that they'll probably add a new command to the SD command set to
allow accessing the additional memory. Systems that don't support that
command will only be able to see the first 4GB of the SD card.
What I don't understand is why a digital camera I bought (Canon
PowerShot SD100) says in its manual that only cards up to 256MB should
be used. I haven't tried using a larger card with the camera but I
can't really think what reason there would be for the camera being able
to use 256MB cards but not 512MB or 1GB.
Thanks again for giving me a clue.
Regards,
Craig
Perhaps they keep track of the cards in RAM, and don't have the space |
for more than a 256MB card?
Just a guess.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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Richard H.
Guest
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| Posted:
Thu Jan 06, 2005 4:55 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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Craig wrote:
| Quote: | Ok, I really haven't used Usenet in about a decade
and now in both of my first two posts I look like
an idiot.
|
ROFL! Been there ... :-)
| Quote: | What I don't understand is why a digital camera I
bought (Canon PowerShot SD100) says in its manual
that only cards up to 256MB should be used. I
haven't tried using a larger card with the camera
but I can't really think what reason there would
be for the camera being able to use 256MB cards
but not 512MB or 1GB.
|
Good question. I've heard rumor of this issue from other consumers, but
I don't know the reasoning, or if it's really valid. (Maybe the docs
were just printed before they could test the newer cards?) |
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Roberto Waltman
Guest
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| Posted:
Thu Jan 06, 2005 4:57 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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| Quote: | What I don't understand is why a digital camera I bought (Canon
PowerShot SD100) says in its manual that only cards up to 256MB should
be used. I haven't tried using a larger card with the camera but I
can't really think what reason there would be for the camera being able
to use 256MB cards but not 512MB or 1GB.
Thanks again for giving me a clue.
|
Ignoring possible technical limitations, one reason could be that no
cards larger than 256MB were available when the camera was designed
and tested. It would make sense for the manufacturer to claim that the
camera works only with devices they could actually verify.
(Just an educated guess...)
Roberto Waltman.
[ Please reply to the group,
return address is invalid ] |
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Mike Fields
Guest
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| Posted:
Thu Jan 06, 2005 7:41 am Post subject:
Re: Addressong Secure Digital (SD) > 16MB |
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"Roberto Waltman" <usenet@rwaltman.net> wrote in message
news:vfvot0t0a7dn9es3n2obq0jgi5147kp0au@4ax.com...
| Quote: | What I don't understand is why a digital camera I bought (Canon
PowerShot SD100) says in its manual that only cards up to 256MB should
be used. I haven't tried using a larger card with the camera but I
can't really think what reason there would be for the camera being able
to use 256MB cards but not 512MB or 1GB.
Thanks again for giving me a clue.
Ignoring possible technical limitations, one reason could be that no
cards larger than 256MB were available when the camera was designed
and tested. It would make sense for the manufacturer to claim that the
camera works only with devices they could actually verify.
(Just an educated guess...)
Roberto Waltman.
[ Please reply to the group,
return address is invalid ]
|
I believe part of the issue was what they were able to test with, but it
may also be related to how they implemented the file system in the
camera and if it can handle the larger "disk". Part of that issue has
been a "gotchya" for some time where people have reformatted some
of the larger Compact Flash type cards (or SD etc) under windows
XP and found their cameras can no longer handle them -- seems
windows "helps" you by deciding that the bigger cards should be
formatted FAT32 when the OS in the cameras can only handle
FAT16. You have to reformat to a FAT16 file system for the
camera/gps/whatever to be able to handle it. The nice thing about
standards is there are so many to chose from ...
mikey |
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