Memory cards are the standard devices for recording your images to when using a digital camera. They are descendents of film in a way, and are the medium in which your imagery sits before viewing. They differ from film, of course, in that they are flash storage devices, similar in idea to external hard drives that are used with computers. Memory cards permit re-recording and overwriting so as to allow infinite use, and do not require dedicated power sources to store or contain data.
Memory cards are available in a variety of shapes, sizes, capacities, speeds, and so on. The most important and first rule to follow is to purchase a memory card that is compatible with your device. Most cameras are compatible with CompactFlash (CF), Secure Digital (SD), or Memory Stick style cards, although other types do exist (such as miniSD, microSD, XD, and XQD). Consult your manual or check your camera to see which type or formats are accepted. Once the general format has been determined, you can then begin to consider the different types and features that are offered.
Recently, and especially in professional-grade cameras, dual memory card slots have been integrated into the design allowing you to use up to two memory cards at a time. The most common combinations are two SD slots, one CF and one SD slot, or one Memory Stick and one SD slot. Another combination, which is currently only featured on the Nikon D4, is having one CF card slot and one slot to accept the newly introduced XQD memory card.
Expanding on the memory card format, cards come in different capacities ranging from as little 1GB up to 256GB. A card’s capacity is fairly self-explanatory, though it should be noted that not all cameras support card capacities over a certain limit. Even though there are memory cards available in capacities up to 256GB, many entry-level and intermediate-grade cameras cannot support these cards. Before assuming it is best to buy a card with the greatest amount of space, make sure you are working within your camera’s limits. Another note regarding using cards with such great capacity is that it is often preferred to have several small-capacity cards rather than one large-capacity card. Splitting the amount of memory you bring with you across numerous cards gives you the versatility to use individual cards for different tasks. For instance, if traveling, you can use one card per day to keep a succinct and orderly record of which day’s photographs are on which card. On the other hand, if working with HD video or other shooting-intensive applications, a large-capacity card might suit you better so you can avoid running out of space and having to switch cards as often.
Another consideration when deciding upon card capacities is the type of files you generally shoot, and how large your average file size is. If you are working with a small 12 megapixel point-and-shoot camera and only shooting JPEG files, you can record upwards of 8,000 images to a single 32GB memory card. But if you are working with a full-frame DSLR and recording both RAW and JPEG file types simultaneously, you might only get 500 or so images per 32GB memory card.
Another determinant for choosing a memory card is how fast its read and write speeds are. This, again, is dependent on your shooting needs and the camera you are using. The exception in this case is that higher numbers are always “better;” whether or not you actually need a card to read and write a file at 150MB per second is a different question. When looking at different memory cards, there will often be two numbers shown: read and write speed. Write speed refers to the transfer rate, in MB per second, that the card can receive files from the camera. The higher the number, the faster images can be recorded. Read speed is similar; however, this rate, also measured in MB per second, refers to how quickly images can be transferred from your card to your computer.
Higher write speeds enable faster continuous capture with minimal backup times. Faster read speeds enable quicker transfer times from your card to your computer for importing images. Higher performance cards are more essential for video recording, as more data is being continuously written to your cards, versus shooting single, still images. Some memory cards will also display these speeds in terms of "x" (such as 400x or 1000x). This "x" is the multiplication of a standard data-transfer rate of a CD-ROM drive, and a simple formula is that 1x=150KB/s; therefore a 400x memory card can transfer data at a rate of 60MB/s (400 x 150 = 60,000 / 1000 = 60).
Additionally, memory cards can be broken down into different classes or ratings, and these differ depending on memory card format:
SD is more of a catch-all term for the shape and size of this format memory card. A true SD card is becoming more and more obsolete with the advent of SDHC and SDXC cards. The difference in these cards is their maximum capacity: standard SD cards have a maximum capacity of 2GB; SDHC cards have a capacity greater than 2GB but less than 32GB; and SDXC cards are greater than 32GB and up to a theoretical limit of 2TB, although the current largest SDXC card is 256GB. Furthermore, SD card types are divided into speed classes. These classes are based on a minimum sustained data writing speed (with the maximum write speed often surpassing this number by quite a lot). Class 4 equates to a minimum 4MB/s sustained write speed while Class 10 means a minimum 10MB/s write speed.
There is also a UHS (Ultra High Speed) Speed Class. The current standard for this is UHS-I, or UHS Speed Class 1. UHS-I cards have a minimum write speed of 10MB/s, like a Class 10 card, but support the UHS bus interface for a higher potential of recording real-time broadcasts and larger HD video file sizes. As with general read and write speeds, these speed classes, or minimum sustained write speeds, relate to better performance—the higher the number is. However, these numbers are mainly used as a reference tool for video recording since it is a continuously recorded medium. Depending on the rate at which your camera can record video, you should select a card that meets or outperforms this number to ensure clear, fluid recordings.
These classes and standardizations are also applicable to microSD and miniSD cards; however, such cards are physically smaller in size and are often used in smaller devices, such as cellular telephones. These cards can also be adapted through the use of a standard SD-size passive adapter to function in devices that only accept SD-sized cards. The other difference these smaller cards have is the lack of a physical write-lock switch on the exterior of the card, that would otherwise permit manual locking of the card, similar to the write-protection tab of a VHS cassette.
Similar to SD cards, CF cards also have a class system; however, it is not quite as extensive as the division between different classes and designations. Older CF cards utilized a communication protocol called PIO (Programmed Input/Output). This protocol was divided into modes depending on the theoretical performance of a given card. Mode 6, the highest level, allowed a maximum transfer rate of 25MB/s. More recently, CF cards have adopted a new method of communication called UDMA (Ultra Direct Memory Access). UDMA cards are also divided into modes, with the lowest, Mode 1, permitting up to 25MB/s and the current highest, Mode 7, permitting transfer rates up to 166MB/s. As with SD cards, the higher the number, the better the performance for intensive imaging tasks such as video recording or continuous shooting.
Memory Stick PRO Duo cards are a proprietary memory type used in many Sony devices. These cards are similar in size to SD cards and are smaller than the original incarnations of the Sony Memory Stick. Currently, only two types of Memory Sticks are available, either the Memory Stick PRO Duo or the Memory Stick PRO-HG Duo. The PRO-HG Duo is the faster of the two types, offering approximately four times faster performance over the PRO Duo.
The newest type of memory card that is currently being used is the XQD card. This format is designed for more contemporary means of image production, including HD video recording and continuous high-resolution image capture. XQD cards are currently available in two classes: the standard XQD and the XQD S-series. The standard class supports transfer speeds up to 125 MB/s while the S-series supports up to 168 MB/s. The XQD memory card type has a theoretical capacity limit greater than 2TB, although currently the largest capacity card offered is 64GB. The Nikon D4 DSLR is the first camera to support the use of XQD card types.
While memory cards are generally thought of as a secure and dependable means for storing images and data, there are times when they can fail and result in a loss of your imagery. This is similar to computer drives crashing, and just the same, it is always a good idea to keep a consistent and orderly backup of your files. If a memory card fails before you have the chance to back up its data, there are programs available to help you recover lost files. These programs, which are often included with the purchase of a memory card, work to scour the memory card’s lingering data to piece together any files that may have become corrupt, lost, or even deleted.
When you delete an image from a memory card, it is often never fully deleted immediately; this is a good thing. It isn’t until you format your card that traces of an image file are completely erased. Because of this, tools like SanDisk’s RescuePRO and Lexar’s Image Rescue 4 can piece together files that are not easily read by your camera or even by your computer when simply viewing the contents of the card. These programs utilize complex algorithms to scan and recover all types of data, including image files as well as other document types.
When working with these tools, it is best to use an external card reader and an external hard drive to promote a more secure means of transferring recovered data. These programs usually have an intuitive interface that allows you to visually scan through recovered data and select the files you wish to save to a more secure place. Once you have recovered all of the data you need or that is possible, it is best to then completely re-format your memory card to lessen the likelihood of any future crashes or failures due to any lingering peculiar data structures.
Transferring data between your computer and your memory card can be accomplished in a couple of ways: either by connecting your camera to your computer with a cable, or through the use of a dedicated card reader. A memory card reader is the preferred method for moving your data between card and computer, due to its versatility and the simple fact that when you use your camera as a card reader, you are asking the camera battery to do additional work. Additionally, card readers often feature ports to accept several kinds of memory cards for greater versatility when working with multiple cameras or card formats. Dedicated card readers are bus-powered and connect directly to your computer, usually via a USB 2.0 or 3.0 interface. USB 3.0 memory card readers permit faster transfer speeds due to the 3.0 specification, and they are all backwards compatible with USB 2.0 ports for devices without USB 3.0 compatibility.
Part of memory cards' appeal is how small they are in comparison to some external hard drives and other storage formats. When traveling, it is much more feasible to carry several memory cards than only one or two cards and a computer to facilitate offloading images from your cards. This small form factor can also be an issue, though, because it is easy to misplace or mix up such small items with other similar cards. An ideal solution is to use a memory card case when traveling, or for storage at home. These small cases provide a dedicated location for keeping certain sized memory cards, and offer protection from crushing, impacts or weather. Additionally, cases are available to hold several different kinds of media or memory card formats.
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