Card failures cause more alarm for people than drive failures do, partly because the images on the card cannot be shot again, and partly because of the wording of the warning, which implies that the pictures are already lost. In the overwhelming majority of cases they have not moved at all.
A memory card consists of three components stacked together. First, there are the NAND flash dies; this is where your photographs physically live, as charge held in individual cells. Second, there is a controller, a small processor that decides which physical block each logical address corresponds to, distributes writes across the card so that no one area wears out before the others, and hides failed blocks from view. Finally, there is a file system, usually FAT32 on smaller cards or exFAT on larger ones, which is essentially nothing but a directory listing recording the name, size and starting block of every file.
That directory is just a tiny fraction of the card (a few hundred kilobytes describing tens of gigabytes of pictures), and it is also the part most likely to be damaged, because it is rewritten every time a frame is saved or deleted, while the photographs themselves are written once and then left untouched. If you pull the card out mid-write, let the camera battery die in the middle of a burst, or have contacts that have gone intermittent, it is usually the directory that tears. At this point your computer can't find a usable file system, concludes there is nothing on the card worth reading, and asks if you would like to set up a new one. Not one image has been touched at that point.
Everything that turns a full recovery into a partial one happens in the next thirty seconds. Accept the format and a clean, empty directory is laid over the damaged one, so the faster path back is eliminated and only the slower one is left. Put the card back in the camera to try a test shot, and new data will then be stored in blocks the controller believes to be free; because of wear levelling you do not have any control over where those physical blocks are, so a single frame can land anywhere. Neither of these actions can be undone, and neither can be reversed by anyone at any cost.
So the best thing to do with a misbehaving memory card is the thing which feels the least like taking an action. Eject the card, store it somewhere safe, and stop. Until a format or a new write takes place, every picture is sitting in the flash at the exact location the camera left it, and the odds are as good as they will ever be.
A few unglamorous causes explain a surprising share of calls. Full-size SD cards have a sliding write-protect tab on one edge that can get knocked into the locked position inside a bag, and a locked card may read erratically or refuse to read altogether. The contacts pick up skin oil and grit, and cleaning them with a dry cloth costs nothing. Readers themselves also cause more of this than anyone gives them credit for. The spring contacts inside a cheap adapter lose tension after a few hundred insertions, a laptop slot that has taken thousands of cards is no better, and either will produce read errors on media that a decent powered reader handles without a murmur. Test the card in a different reader on a different computer before you conclude anything about the card itself.
One more check is worth running, because it explains a whole category of failures that look like corruption but are not. Cards bought cheaply through online marketplaces are frequently counterfeit, with the controller reprogrammed to report a capacity that the flash simply does not have. A card sold as 512 GB may only hold 32 GB; it accepts everything you shoot, discards or wraps around the surplus, and appears perfectly fine right up until you try to read the later files. If the card was suspiciously cheap and the failures started once it filled up, that is very likely what you are looking at, and no recovery can bring back data that was never stored in the first place.
The list of things not to do is shorter but much more important. Don't format the card, however reasonably the box asks you to. Don't take a test shot. Don't allow free software to write its results back onto the card it is reading, which is comfortably the most common way a fully recoverable shoot ends up as a partial one. And if the plastic is cracked or the contacts look chewed, stop completely: one more flex will break the bonds inside and move the job into the chip-level bracket, which is going to cost more and take longer.
A card that refuses a format, reports only a fraction of its printed capacity, identifies itself as 0 MB, or has become permanently read-only may sound worse than it really is. All four point at the controller instead of the flash. Controllers do deliberately go into a locked read-only state if their internal wear statistics look bad, and they lose their translation tables completely when power is cut at the wrong moment. In either case, the chip in the middle has stopped responding sensibly, and no consumer utility will reach beyond it. The low-level format tools suggested on forums are a reliable way to finish off a card that still holds something you want to keep.
Getting round a dead controller means going round it instead of fighting it. If it still responds in some way, the card is imaged behind a write blocker using many slow, repeated passes. If it doesn't respond at all, the flash is read directly from the silicon with a specialist programmer, and then the real work begins: the private scrambling, block interleaving and error correction used by the controller need to be reconstructed from first principles before anything resembling a file appears. Full-size SD cards often have two separate packages, one for the flash and another for the controller. Most microSD cards are monolithic, meaning the die and the controller are moulded into a single unit, which is why the read has to be taken from test pads on the body of the card itself. That is chip-level work, and one of the stated exceptions to only paying if we recover your data: it takes 50% of the quoted figure upfront, with the balance only if we recover your data.
Your card isn't what gets worked on. The first step is a sector-by-sector image of the card, taken through a write blocker, and every decision after that is made against that copy; so if your card is already deteriorating, the recovery cannot push it any further, and no mistake can ever reach the original. Where enough of the file system survives within that image, it is repaired and the folder tree comes back looking as the camera left it, including the filenames. Where it doesn't, the frames are found by their content instead: a JPEG, a CR3, an NEF and an ARW each begin with a recognisable signature, and they can be lifted out of unallocated space without any directory at all.
Two things get checked before anything is described as recovered. Each still is rendered rather than simply listed, as there is a difference between a filename appearing in a results pane and the same image actually drawing on the screen. Video files require even greater care, because long clips are written out across scattered blocks and a partial overwrite tends to damage a file somewhere in the middle rather than remove it cleanly, which is another reason why you should not shoot anything else on a card once it has started misbehaving.
Cards from Berkshire are delivered to us in a pretty predictable mix. Some have product or conference video taken at the various business parks, some have estate agency or property work shot around Warfield and Binfield, others hold event or motorsport coverage captured along the M4 corridor, and then there are students on media and design courses in Reading holding a whole term's worth of field recordings on one card. These cards live in bags, get swapped with cold hands on wet mornings, pick up damp that never quite leaves, and go through a few thousand insertion cycles that the contacts were never really specified for. The wear is real rather than theoretical.
Packing is easy. First get a quote, either over the phone or by using our free online diagnostic. Then place the card between two pieces of folded stiff card (so as to prevent it from bending), slide that into a padded envelope, and send it by tracked, insured post to Guildford Data Recovery, Building 2, Ground Floor, Guildford Business Park, Guildford, GU2 8XH. The drive from Bracknell is roughly forty minutes by road on the A322 and the A3, should you wish to drop it off at the lab yourself; the lab is open Monday to Friday, 9am to 5:30pm, with no need to book an appointment, and nothing is collected anywhere on this network. Posting a single card will cost you just pennies, there is no charge for the diagnostic, which closes 2 working days after booking in, and the recovery figure for memory cards, USB sticks and pen drives is £250 + VAT.
The most useful thing you can do with a failing card is nothing at all. A format prompt is a damaged directory, and every frame is sitting behind it exactly where the camera wrote it. This will remain the case until something new is written. Remove the card, leave it alone, and let a working copy take all the risk.
Free diagnostic completed within 2 working days of booking in your device, then one fixed written quote, and in most cases you only pay if we recover your data. Cards and USB sticks £250 + VAT, and any single drive or SSD £300 + VAT.