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#1
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Fast and slow SD Cards
I was going to get a spare SD Card for a recorder and the tech
support guy said to get one which was under 2GB and not high speed. I can understand the recorder may not support SDHC and won't recognise a 2GB+ card. But what is that about not using a fast SD Card. Surely my recorder ought to work whatever the speed of the SD memory card? Was he talking crap? |
#2
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Fast and slow SD Cards
dave wrote:
I was going to get a spare SD Card for a recorder and the tech support guy said to get one which was under 2GB and not high speed. I can understand the recorder may not support SDHC and won't recognise a 2GB+ card. But what is that about not using a fast SD Card. Surely my recorder ought to work whatever the speed of the SD memory card? Was he talking crap? May he's just saying that investing in really fast cards isn't going to help much. A recorder (sound? camcorder?) has a fixed write rate so when recording you don't need a card much faster than that. Having a fast card can however be a good thing when transferring the files to a computer. -- Bertrand |
#3
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Fast and slow SD Cards
"dave" wrote in message
news I was going to get a spare SD Card for a recorder and the tech support guy said to get one which was under 2GB and not high speed. I can understand the recorder may not support SDHC and won't recognise a 2GB+ card. But what is that about not using a fast SD Card. Surely my recorder ought to work whatever the speed of the SD memory card? Was he talking crap? The speed rating of the card is the fastest that it can manage, not the speed that it *must* run at. A fast card will transfer slowly when necessary! It will cost more though, so if you don't need fast transfer speeds, then you can save money by buying a slower one. |
#4
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Fast and slow SD Cards
europe.news.astraweb.com wrote:
"dave" wrote in message news I was going to get a spare SD Card for a recorder and the tech support guy said to get one which was under 2GB and not high speed. I can understand the recorder may not support SDHC and won't recognise a 2GB+ card. But what is that about not using a fast SD Card. Surely my recorder ought to work whatever the speed of the SD memory card? Was he talking crap? The speed rating of the card is the fastest that it can manage, not the speed that it *must* run at. A fast card will transfer slowly when necessary! It will cost more though, so if you don't need fast transfer speeds, then you can save money by buying a slower one. I don't have a camera that uses SDHC, but I have an mp3 player that does. I have some very slow (read cheap) 16gb SDHC cards that are that take ages to load data onto, but once the player they are just as good as the fastest. Allen |
#5
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Fast and slow SD Cards
I's ONLY SDHC cards that are 4x and 6x.
The SDHC technology was specifically developed to allow higher speed read/writed. To handle SDHC card's higher speed, the device must have read and write buffers to stop over-runs (which loses data). So the tech support guy wasn't talking crap. |
#6
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Fast and slow SD Cards
dave wrote:
I was going to get a spare SD Card for a recorder and the tech support guy said to get one which was under 2GB and not high speed. Maybe he meant, "Don't get a High Capacity card". That would, of course be a SDHC, which may not in fact, be compatible with your recorder. As far as speed is concerned, high speed cards are really nice for downloading images to your computer. Most manufacturers don't advertise the card's speed but some do. My SD cards that are rated at 150X do a very good job. I have recently seen a SDHC card rated as 300X, but I have not used it. Bob Williams |
#7
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Fast and slow SD Cards
With respect Bob, virtually all SDHC card maufacturers do advertise the
card's speed - on the card itself. You'll see a number (usually within a circle) which indicates that card's speed and is called "Class". Respectively, Class 2 is rated at 2.0 MBytes per second. Class 4 is rated at 4.0 or 4.8 MBytes per second. Class 6 is rated at 6.0 MBytes per second. Class 10 is rated at 10.0 MBytes per second. Class 15 is rated at 15.0 MBytes per second. Class 20 rated at 20.0 MBytes per second. Class 22 is rated at 22.5 MBytes per second. Class 30 is rated at 30.0 MBytes per second. Class 40 is rated at 40.0 MBytes per second. Class 45 is rated at 45.0 MBytes per second. Regards... |
#8
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Fast and slow SD Cards
With respect John, I was trying to keep things simple. Whenever data is
written/read from a storage device, to avoid loss of data, buffers have to be used. Buffers are invariably configured to read/write one or more blocks (in the context of SD/SDHC the block and cluster size varies card to card). This is where I was coming from when I spoke of buffers. If you require a more geeky treatment, I can do no better than to quote what is described in Wikki (but please - do put it in the context of reading/writing blocks from cards). QUOTE Compatibility issues with 4 GB and larger cards Devices that use SD cards identify the card by requesting a 128-bit identification string from the card. For standard-capacity SD cards, 12 of the bits are used to identify the number of memory clusters (ranging from 1 to 4096) and 3 of the bits are used to identify the number of blocks per cluster (which decode to 4, 8, 16, 32, 64, 128, 256 or 512 blocks per cluster). In older 1.x implementations the standard capacity block was exactly 512 bytes. This gives 4096 x 512 x 512 = 1 gigabyte of storage memory. A later revision of the 1.x standard allowed a 4-bit field to indicate 1024 or 2048 bytes per block instead, yielding up to 4 gigabyte of memory storage. Devices designed before this change may incorrectly identify such cards, usually by misidentifying a card with lower capacity than is the case by assuming 512 bytes per block rather than 1024 or 2048. For the new SDHC high capacity card (2.0) implementation, 22 bits of the identification string are used to indicate the memory size in increments of 512 kBytes. Currently 16 of the 22 bits are allowed to be used, giving a maximum size of 32 GB. All SD cards with a capacity larger than 4 GB must use the 2.0 implementation at minimum. Two bits that were previously reserved and fixed at 0 are now used for identifying the type of card, 0=standard, 1=SDHC, 2=reserved, 3=reserved. Non-SDHC devices are not programmed to read this code and therefore cannot correctly identify SDHC or SDXC cards. All SDHC readers work with standard SD cards. Many older devices will not accept the 2 or 4 GB size even though it is in the revised standard. The following statement is from the SD association specification: "To make 2 GByte card, the Maximum Block Length (READ_BL_LEN=WRITE_BL_LEN) shall be set to 1024 bytes. However, the Block Length, set by CMD16, shall be up to 512 bytes to keep consistency with 512 bytes Maximum Block Length cards (Less than and equal 2 Gbyte cards)." [edit] 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 4 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 4 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 some devices. [edit] SDHC cards with greater than 32 GB capacity Similarly to the above, as of version 2.00 of the specification, the capacity of an SDHC card is limited to 32 GB. However, while not strictly adhering to that standard, it is in principle possible to create SDHC-like cards of up to 2048 GB capacity. SDHC cards have fixed sector size of 512 bytes. [edit] /QUOTE You'll note from above, SD cards are limited to 4GB. And although you may have done, I have never seen an SD card higher than Class 4. Regards |
#9
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Fast and slow SD Cards
wrote in message
... With respect Bob, virtually all SDHC card maufacturers do advertise the card's speed - on the card itself. You'll see a number (usually within a circle) which indicates that card's speed and is called "Class". Respectively, Class 4 is rated at 4.0 or 4.8 MBytes per second. Class 6 is rated at 6.0 MBytes per second. [] Regards... Doesn't seem to apply to the SDHC cards I have: SanDisk - labelled class 4, and 15MB/s DaneElec- labelled class 6, and 133X (19.95MB/s) David |
#10
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Fast and slow SD Cards
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