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SD---SDHC?

vic cross
Posted 14/03/2010 - 07:57 Link
I can't remember which thread it was in so I've started again. Just recently there was some debate as to whether SD finished at 2GB or at 4GB. I thought it was 4GB as I have 2 cards which are 4GB with just SD on them. someone suggested that they were really SDHC. I've just shot some random pics for test on one of these cards and put it in a very old card reader (pre SDHC) which was buried in my cupboard as both my desktop and laptop have card readers built in, and it read the card no problem. So where does SD/SDHC start? I think it must be SD to 4GB then SDHC stats at 8GB? CHEERS Vic.
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.
Edited by vic cross: 14/03/2010 - 07:58
thoughton
Posted 14/03/2010 - 08:56 Link
It was me who mistakenly said SD ends at 4GB. It ends at 2GB. 4GB and above and it should be SDHC.
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Edited by thoughton: 14/03/2010 - 08:57
bretti_kivi
Posted 14/03/2010 - 09:31 Link
SD to (officially at least) 2GB, SDHC above that, though there are some 4GB cards that are SD only. Not many, mind...

Bret
paulgee20
Posted 14/03/2010 - 14:04 Link
Many people advertise SD cards over 2GB But in reality they are all SHDC in fact. Usually not mentioned until in the small print). As Brett says you can find the odd SD to 4GB but few and far.....

Paul
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vic cross
Posted 14/03/2010 - 15:08 Link
I must have 2 of the odd ones then. I got them some time ago, (when I got my K10) from "MyMemory" Jersey or Guernsey. It doesn't state what speed they are, 2/4/or6 but they work well enough. I have since graduated to 8GB and then to 16GB in my K7 but still use the 4GB cards to transfer various things.
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.
whelmed
Posted 14/03/2010 - 15:24 Link
Basically it comes down to the number of bits on the memory cards. While a 32-bit number, in theory, can address 4GB worth of data ... it'd have to be an signed 32-bit number which is 2^32-1 (2 to the power of 32 minus 1) addressable bytes. So in reality, that's 1 byte short of 4GB - which can cause problems. I suppose it would be possible, but also unlikely that manufacturers would go this route. This is the same reason that why on newer computers if you have a 32-bit version of Windows that only 3GB of memory is useable.

I hope that makes sense, though it'll probably sound more like incoherent engineering babble
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Edited by whelmed: 14/03/2010 - 15:26
Anvh
Posted 14/03/2010 - 16:15 Link
Whelmed I believe all cards sizes have a -1 byte so it shouldn't be a problem.

btw I wonder why they didn't make the 645D SDXC ready
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Edited by Anvh: 14/03/2010 - 16:15
bretti_kivi
Posted 14/03/2010 - 18:10 Link
that's what I figured. Then I read the wikipedia page and saw a *lot* of this is definitions from teh SD authority.

Bret
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Oggy
Posted 14/03/2010 - 18:34 Link
That would be this page. Good stuff.
polchraine
Posted 14/03/2010 - 23:30 Link
Anvh wrote:
Whelmed I believe all cards sizes have a -1 byte so it shouldn't be a problem.

btw I wonder why they didn't make the 645D SDXC ready

It may be ...

I believe that SDHC devices which support SDXC cards provided they meet certain criteria and the exact implementation of the spec.
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vic cross
Posted 15/03/2010 - 16:15 Link
I thought ask a simple question I'll get a simple answer!!!!
No such luck. I'm as confused as ever. Not to worry though I've got 2 of them and they work so that's OK. CHEERS Vic.
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.
Anvh
Posted 15/03/2010 - 16:32 Link
This from Wiki and it answer your question I believe

Standard-SD cards (non-SDHC) with greater than 1 GB capacity

The SD Card Association's current specifications define how a standard SD (non-SDHC) card with more than 1 GB and up to 2 GB capacity should be designed. These cards should be readable in any SD 1.01 devices that take the block length data into account. Any 1 GB or lesser card should always work (so the key question is how one's reader handles block length).

According to the specification, the maximum capacity of a standard SD card is defined by (BLOCKNR x BLOCK_LEN), where BLOCKNR may be (4096 x 512) and BLOCK_LEN may be up to 2048. This allows a capacity of 2 GB. The main problem is that some of the card readers support only a block (aka. sector) size of 512 bytes, so greater than 1 GB non-SDHC cards may cause compatibility difficulties for users of such devices.

SD and SDHC compatibility issues

The SDHC specification was completed in June 2006, but by that time, non-standard high-capacity (>1GB) SD cards (based on the older 1.x specification) were already on the market. The two types of storage cards were not interchangeable, creating some confusion among customers. SD and SDHC cards and devices have these compatibility issues :
- Devices that do not specifically support SDHC do not recognize SDHC memory cards. Some devices can support SDHC through a firmware upgrade.
- SDHC devices are backward compatible with SD memory cards.
- Some manufacturers have produced 4 GB SD cards that conform to neither the SD2.0/SDHC spec nor existing SD devices
Stefan
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Edited by Anvh: 15/03/2010 - 16:32
Glover
Posted 15/03/2010 - 16:51 Link
Answered simply, sd is upto 2 gb with a few 4gb been made. anything other than those few 4gb sd that are above 2gb are sdhc.
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