SD card: 1G vs 2G
in [Home Built PC]
|
From: Man-wai Chang on 20 Jun 2010 06:16 What are their difference? Why is a card reader able to read the 1G but not the newer 2G card? Thank you in advance!
From: Conor on 20 Jun 2010 06:29 On 20/06/2010 11:16, Man-wai Chang wrote: > What are their difference? > > Why is a card reader able to read the 1G but not the newer 2G card? > > Thank you in advance! Some are a different density and the reader has problems with it - the same as early computers when larger capacity DIMMS came out - they'd see a double sided one but only half the capacity of a single sided high density. -- Conor www.notebooks-r-us.co.uk
From: Paul on 20 Jun 2010 06:48 Man-wai Chang wrote: > What are their difference? > > Why is a card reader able to read the 1G but not the newer 2G card? > > Thank you in advance! http://en.wikipedia.org/wiki/SDHC#SDHC "Standard-SD cards (non-SDHC) with greater than 1 GB capacity According to the specification,[19] the maximum capacity of a standard SD card is defined by (BLOCKNR � BLOCK_LEN), where BLOCKNR may be (4,096 � 512) and BLOCK_LEN may be up to 2,048. This allows a capacity of 4 GB. The main problem is that some of the card readers support only a block (or, sector) size of 512 bytes, so greater than 1 GB non-SDHC cards may cause compatibility difficulties for users of such devices." "SDHC To increase addressable storage, SDHC uses sector addressing instead of byte addressing in the previous SD standard." So up to 1GB, byte addressing, with 512 byte blocks, should always work. Devices bigger than 1GB, may need larger sector size, like 2048 bytes. And once over 4GB, the standard changes to SDHC. Paul
From: Man-wai Chang on 20 Jun 2010 07:08 > This allows a capacity of 4 GB. The main problem is that some > of the card readers support only a block (or, sector) size of 512 bytes, > so greater than 1 GB non-SDHC cards may cause compatibility difficulties > for users of such devices." > So up to 1GB, byte addressing, with 512 byte blocks, should always work. > Devices bigger than 1GB, may need larger sector size, like 2048 bytes. You meant if I formatted a 4G SD card using 512-byte blocks, the old card reader might be able to read it like it did with older 1G SD cards?
From: Man-wai Chang on 20 Jun 2010 07:08
> Some are a different density and the reader has problems with it - the > same as early computers when larger capacity DIMMS came out - they'd see > a double sided one but only half the capacity of a single sided high > density. Further detail? :) |