Talking about SD, CF, SDHC, What's the difference?

SD, CF,  SDHC, What's the difference?

CompactFlash Card

A 64 MiB CompactFlash Type I card

Media type Mass storage device format
Encoding Various file systems
Capacity 2 MiB to 184 GiB
Developed by SanDisk
Dimensions 43×36×3.3 mm (Type I) 43×36×5 mm (Type II)
Weight 10 grams (typical)
Usage Digital cameras and other mass storage devices
Extended from PCMCIA / PC
SD Card write speeds on D90

Secure Digital (SD) cards are much smaller and lighter than Compact Flash (CF) cards. They have a 9 pin interface. (SD cards have a 50 pin interface) and this limits them to 4-bit data transfer bus rather than the 16-bit data transfer bus of CF cards. In principle this makes their maximum possible transfer speed slower, but in practice there is little difference when used with current digital cameras. In the past SD cards were more expensive than CF cards and were not available in as high a capacity versions, but this no longer applies.

Secure Digital (SD) is a non-volatile memory card format developed by Matsushita, SanDisk, and Toshiba for use in portable devices. Today it is widely used in digital cameras, handheld computers, PDAs, mobile phones, GPS receivers, and video game consoles. Standard SD card capacities range from 4 MB to 8 GB, and for high capacity SDHC cards from 4 GB to 64 GB as of 2008.

The format has proven to be very popular. However, a change in the format, while allowing capacities greater than 4 GB (SDHC), has created compatibility issues with older devices which cannot read the new format. Since SDHC format cards have the same physical shape and form factor as the older format, this has caused considerable confusion for consumers. SDHC cards require an SDHC capable device firmware, generally not found with older devices.

Technical Phototography Article><a href=The SD card format is limited to 2GB. In principle they could be made up to 4GB using FAT32 formatting which isn't part of the standard SD specification (SD uses FAT12 or FAT16 formatting). Recently a new SDHC (SD High Capacity) standard has been introduced which uses the same physical form factor but which uses a different memory addressing method (sector addressing vs byte addressing) and enables cards to be produced with capacities from from 4GB to 32GB. Cameras must be SDHC compatible to use SDHC cards, though most SDHC compatible cameras should be able to use regular lower capacity SD cards. However SDHC is not backwards compatible with SD and that means a 4GB SDHC card will not work in a camera designed only for use with SD cards.

The Secure Digital High Capacity (SDHC) format, announced in January 2006 and defined in Version 2.0 of the SD specification, supports cards with capacities up to 32 GB. The SDHC trademark is licensed to ensure compatibility.

SDHC cards are physically and electrically identical to standard-capacity SD cards (SDSC). The major compatibility issues between SDHC and SDSC cards are the redefinition of the Card-Specific Data (CSD) register in Version 2.0 (see below), and the fact that SDHC cards are shipped preformatted with the FAT32 file system.

Version 2.0 also introduces a High-speed bus mode for both SDSC and SDHC cards, which doubles the original Standard Speed clock to produce 25 Mbyte/s.

SDHC host devices are required to accept older SD cards. However, older host devices do not recognize SDHC or SDXC memory cards, although some devices can do so through a firmware upgrade. Older Windows operating systems released before Windows 7 require patches or service packs to support access to SDHC cards.

The Secure Digital eXtended Capacity (SDXC) format, announced in January 2009 and defined in Version 3.01 of the SD specification, supports cards up to 2 TB (2048 GB), compared to a limit of 32 GB for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's exFAT file system as a mandatory feature, although some portable devices rated for SDHC will also accept a 64GB SDXC card if it is reformatted as NTFS instead of exFAT.

The 3.0 specification also introduced the Ultra High Speed (UHS) bus for both SDHC and SDXC cards, with interface speeds from 50 Mbyte/s to 104 Mbyte/s for 4-bit UHS-I bus.

Version 4.0, introduced in June 2011, allows speeds of 156 Mbyte/s to 312 Mbyte/s over 4-lane UHS-II bus, which requires additional row of physical pins. Due to the proprietary nature of exFAT file system, BSD and Linux systems do not support it out of the box. There is an open source implementation available  as a FUSE module. The user may reformat the card to contain a different file system (see below). SDXC host devices accept all previous families of SD memory cards. Windows XP SP2 and later, and Apple Mac OS X 10.6.5 and later, support exFAT and SDXC.

Compact digital cameras

SD/MMC cards have replaced Toshiba's SmartMedia as the dominant memory card format used in Digital Cameras. In 2001 SmartMedia had achieved nearly 50% use, but by 2005 SD/MMC had achieved over 40% of the digital camera market and SmartMedia’s share had plummeted, with cards not being easily available in 2007.

A majority of the world’s leading digital camera manufacturers use SD in their product lines, including Casio, Canon, Nikon, Pentax, Kodak, Panasonic, Konica Minolta and Ricoh. Two major brands, however, have stuck to their own proprietary formats in their cameras: Olympus using xD cards, and Sony using Memory Stick. Fuji prior to 2007 also used xD cards exclusively, but has added SD functionality to all of their models since then, while Olympus has released a xD-MicroSD adaptor for their latest cameras.

Digital SLR Cameras

As of 2014, most consumer Digital SLR cameras use SD storage. Some prosumer and professional models continue to use CompactFlash storage, historically for such reasons as better price/capacity ratio, and faster (read/write) transfer rate. Canon's EOS-1Ds Mark III and EOS-1D Mark III have separate card slots for both CompactFlash and SD. Here is the list of the DSLR cameras that use SD cards:
Canon 1D Mark IV SD/CF
Canon 5D Mark III SD/CF
Canon 60Da
Canon 70D
Canon T5
Canon Rebel SL1
Canon Rebel T1i
Canon Rebel T2i
Canon Rebel T3
Canon Rebel T3i
Canon Rebel T4i
Canon Rebel T5i
Canon EOS 1000D/Rebel XS
Canon EOS 450D/Rebel XSi
Nikon DF
Nikon D50
Nikon D40
Nikon D40X
Nikon D50
Nikon D60
Nikon D80
Nikon D90
Nikon D300s - SD/CF
Nikon D600
Nikon D610
Nikon D800 - SD/CF
Nikon D800E - SD/CF
Nikon D3000
Nikon D3100
Nikon D3200
Nikon D3300
Nikon D5000
Nikon D5100
Nikon D5300
Nikon D5200
Nikon D7000
Nikon D7100

SanDisk Memory Compatibility for Nikon DSLR Cameras

The following Nikon cameras support FAT32, allowing the use of memory cards with capacities over 2GB - D100, D200, D300, D2 series, D3, D70, D70s, D80, COOLPIX 8800, COOLPIX 8700, COOLPIX 8400 and all products that support the the SDHC memory card format.

Pentax *istDS K10D (and the Samsung GX-10)
Pentax K100D
Pentax K110D
Pentax K20D (and the Samsung GX-20)
Pentax K200D

Lexar 600 CF CardCF cards also have an onboard microcontroller for the memory which takes some load off the host, but this is currently more of theoretical interest than practical significance. The "Secure" in Secure Digital comes from the card's origin which was concerned with digital rights managements schemes to prevent copying of music! SD cards contain encryption hardware, but it's not used in 99% of all applications and it looks just like flash memory to a digital camera. MultiMediaCards (MMC) are essentially the same as SD cards, but without the encryption hardware and with a few other technical differences.

Which Cards are Fastest Update: Sandisk released their extreme IV series in July of 2006. These cards have a data transfer rate of up to 40 MB/s, which is twice that of the extreme III cards. There are available in 2GB ($89.99), 4GB ($149.95) and 8GB ($299) versions. They share the same rugged construction and wide temperature range as the Extreme III series. For more information see the article on Sandisk Extreme IV cards.

In February 2007 Lexar introduced Professional UDMA (Ultra Direct Memory Access) memory cards. Speed-rated at 300x, capable of a minimum sustained write speed of 45MB per second, and available in capacities of 2GB, 4GB, and 8GB, new Lexar Professional UDMA cards deliver a 125% performance improvement over Lexar's previous generation 133x CompactFlash® product line when the card is used with a UDMA-enabled device.

The second fastest current CF cards seem to be the Sandisk Extreme III series, although the Sandisk Extreme, Sandisk Ultra II and Lexar 80x series cards are close, at least on most DSLRs and certainly on the EOS 20D/30D/40D and Digital Rebel XT/XTi/XS/XSi. The speed difference from the fastest to the slowest in this group is probably about 5%, nor really enough to make much of a difference. The 1GB Sandisk Extreme III card which sells for around $43 on ebay. It also comes with a lifetime warranty and free data recovery software. Even slow 1GB cards don't sell for much under $20, so it's not all that much more for the fastest, most durable card.

The Extreme III series cards have a native write speed of 20 MB/sec, though camera limitations usually drop this to around 5-6 MB/sec. They are also tested at temperatures from -13°F to +185°F (-25°C to 85°C) , which should cover most shooting conditions(!) and Sandisk say that they are better protected against shock. The standard Extreme series are tested over the same temperature range, but have a write speed of 9 MB/s. Though this sounds (and is) slower, in actual use there is very little difference in speed in most cameras. Both the Digital Rebel XT/XTi and EOS 20D/30D top out at about 5-6 MB/sec and even the EOS 1Ds Mk II can't write much faster than about 7-8 MB/s.

The Sandisk Ultra II cards are the same speed as the Extreme cards (9MB/sec write speed), but aren't specified for use over such a wide temperature range. The Sandisk Ultra II 1GB sells for around $25 on ebay.

RiData also have some very fast cards. They are labeled as 150x (22MB/s), but that's their read speed. The specs indicate that they can write at 15 MB/s (100x), still very fast but not quite as fast as the Sandisk Extreme III series cards. They have an operating temperature range of 0°C to 70°C, slightly less than the -25°C to 85°C range of the ruggedized Extreme III cards.

The fastest cards come into their own when transfering data to a PC via an optimized card reader. For example the Sandisk Extreme IV cards when coupled to a fast PC via the Sandisk Firewire 800 card reader can hit transfer speeds close to 40 MB/sec, but with a generic USB 2.0 card reader that transfer rate drops to around 6-7 MB/sec, no faster than a much cheaper 60x card. If you want the ultimate performance out of your ultimate speed memory card, you must be careful which card reader you use.

If the speed of transfer from card to PC isn't important to you, buying the very fastest cards won't be cost effective since they will be no faster in the camera. Just go have lunch while your card transfers data! For comparision, with everything fully optimized you could download the fastest 2GB card to a fast PC via the fastest Firewire 800 card reader in under a minute. A slower card and slower USB 2.0 reader might take 6 minutes. I have an old card reader that would take close to 30 minutes! However if I'm at lunch while the downloading is done, I don't really care how long it takes.

Which Cards are the Cheapest This is a more difficult question since prices can vary all over the place on older, slower cards. It used to be possible to make significant savings by using such cards, but today the faster cards aren't really all that much more expensive in many cases, so going for the "rock bottom" price isn't always the best course of action. The lowest prices are often the result of mail-in rebates or other discount offers which come and go. You just have to keep your eyes open for such offers.

So which card to buy? A few years ago you might pay two or three times as much for a fast card, and large capacity fast cards cost hundreds of dollars (as much as a thousand dollars for some high capacity cards). Back them it didn't make much sense to spend extra on a card that wasn't going to do much for you, so slower cards often made sense. Today fast cards don't cost that much more than slow cards and you can get a fairly fast 1GB card for under $30, so the decision is a bit easier to make. A few years ago you'd might have paid several hundred dollars for a 1GB card, and it would have been slower!

For most cameras probably the best value are the 1GB and 2GB cards with speed ratings around 50x. The slower cards aren't much cheaper and the faster cards don't give all that much extra speed. While your current camera may not benefit from a fast card (if you have a 300D or 10D for example), it's very likely that your next one will!

The highest capacity cards available at reasonable prices are probably the Seagate 8GB Microdrive CF card (type II) which currently sells for around $148, and the Transcend 120x 8GB CF card which sells for around $91, which seems like quite a bargain. There's a compatibility matrix for the 8GB Seagate microdrive on the Seagate Website which lists the cameras with which the 8GB drive has been tested. Personally, I'd be inclined to go with the solid state flash memory rather than the microdrive.

IMPORTANT NOTE:In order to use drives with a capacity greater than 2GB (either solid state or microdrive), the camera must support the use of the FAT32 file system. Most current higher end digital cameras (including the EOS 10D, EOS 20D and Digital Rebel XT as well as the Powershot G6, S50, S60 and S70) do support FAT32. Older cameras (including the EOS D30 and D60) may be limited to the use of 2GB microdrives and memory cards. If you are in any doubt about whether your camera supports FAT32 and can use 4GB and 6BG microdrives, Hitachi have a compatibility matrix chart on their website where you can check. The current 4GB drive is designated "3K6-4". "3K4-4" is an earlier vesion of the 4GB drive. The 6GB drive is the "3K6-6". Drives with the "-2" suffix are 2GB.

Bigger isn't always better Cards are being made in larger and larger capacities. 4GB CF cards are now available for around $70 and 8GB cards for under $150 and if you really want the biggest card around you can get a Sandisk Extreme III 16GB card, though the suggested retail price is $1049.99. You can get one from ebay for only $560, though you can certainly find buy four 4GB cards or even two 8MB cards for less.

Obviously high capacity cards and microdrives have advantages in that you don't need to keep swapping cards when shooting. However there is one disadvantage and that's having "all your eggs in one basket". If the card should fail (which is quite rare, but which can happen), you've lost 4GB worth of images. If you were shooting with 4 x 1GB cards you'd only lose 1GB worth of images if one card failed. This is a factor some photographers take into account when deciding what size memory to use. Of course if failure was equally likely, given long enough both systems would lose the same amount of data, but it would be in smaller chunks with the 1GB cards and it wouldn't all happen on the same shoot! However there's no denying that it's more convenient to have one card than to have to swap between cards.

Cards to buy and Cards to avoid Most of the major CF cards are reliable and most have a good warranty. There are good reports about Viking, Kingston, Lexar and SanDisk.

Although Ebay may be an excellent source for many items, be very careful when buying memory cards though them. There are many fake memory cards being on Ebay. The cards may not be made by the manufacturer advertised, they may not have the advertised capacity or they may not have the advertised speed. There are companies in China and other places who will put any label on a card you want if you buy from them in bulk. Some resellers do just that, buying off-brand, low capacity, low speed cards and putting name-brand, high capacity, high speed labels on them. You may be OK buying from major US retailers, but if you buy a cheap card from a dealer in the far east, you're gambling on getting what you expect, and the odds aren't particularly in your favor. I'd stick with Kingston, Lexar, SanDisk Transcend or Viking.

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