Card Slots and File Handling

Fifty raw frames of a kingfisher leaving its perch come to about 865 megabytes. Written to the SD card in my second slot at that card's guaranteed minimum speed, they would take almost ten seconds to land. The CFexpress card in the first slot is rated many times faster, although the camera sets a limit of its own there. That gap decides which card should take pictures first and what the second card should do.

First-Day Setup put the cards in, formatted them and picked a starting role for the second slot. This chapter goes underneath: why the slots differ in speed, what each second-slot option writes, and how the camera names and numbers files until the numbers run out. Burst memory belongs to Release Modes, Frame Rates and the Buffer, and moving files to a computer to a later part.

01.Two Slots, Two Kinds of Wire

What a Speed Number Measures

A byte is eight bits, each a single on-or-off signal, and a megabyte (MB) is a million bytes, the meaning card makers use. Nikon does not say which megabyte it means, and the other common reading, 1,048,576 bytes, differs by under 5%. A card speed of 90 MB/s therefore moves ninety million bytes every second. Nikon quotes file sizes in the same unit, so a raw file of about 17.3 MB (p. 1012) written at 90 MB/s takes $17.3 / 90 \approx 0.19$ seconds.

Every card has two speeds. Reading copies data off, as a computer does after a shoot, and writing puts data on, as the camera does at every frame. The flash memory chips inside a card write more slowly than they read, so the write figure is the one that matters in the field.

Lanes and Why the Slots Differ

Data moves between camera and card along lanes, each a set of wires carrying bits in single file at a very high rate. Two lanes carry twice what one does, as a second carriageway doubles a road.

The lower slot takes SD cards. UHS-II cards add a second row of contacts that provides two lanes, which the SD Association's standard lets run one each way, at up to 156 MB/s in both directions at once, or both the same way, at up to 312 MB/s in one direction. That 312 MB/s belongs to the bus, the shared connection itself, so no UHS-II card can be written faster in any camera. Older UHS-I cards have one row of contacts and top out at 104 MB/s.

The upper slot takes CFexpress Type B cards, which use PCI Express (PCIe), the family of links joining the parts inside a computer, and NVMe, the command language of computer solid-state drives. Type B has two PCIe lanes, each made of two pairs of wires, one sending and one receiving, so traffic flows both ways at full rate. XQD, an older card format, also uses PCIe and shares the Type B shape and connector, so one slot takes both (pp. 93, 1011). Nikon's recommendation for high-speed frame capture +, the release modes that shoot JPEG bursts at 15 to 120 frames a second, names only upper-slot cards: CFexpress or XQD whose maximum transfer rate is 250 MB/s or higher (p. 1011).

Ceilings and Floors on the Label

A card label can carry two kinds of speed figure. The first is a ceiling, the "up to" number. Lexar rates my SD card at up to 300 MB/s read and 260 MB/s write, and my CFexpress card at up to 3,600 MB/s read, 3,000 MB/s write and 2,600 MB/s sustained write, all from its own internal testing. A ceiling is the card's best on its maker's bench and promises nothing about your camera. The older x rating is one too: a unit is 150 kilobytes per second, so 2000x claims $2000 \times 0.15 = 300$ MB/s, the read figure again.

The second is a floor, a minimum the card must hold while writing continuously, certified by a standards body. On SD cards that is the Video Speed Class: V30, V60 and V90 promise at least 30, 60 and 90 MB/s, and the older U3 mark, which Nikon calls UHS Speed Class 3, also means 30. On CFexpress cards the CompactFlash Association's Video Performance Guarantee does the same job, so a VPG400 card promises a minimum sustained write of 400 MB/s. Plan with floors. My SD card carries V90. Nikon's 250 MB/s recommendation, by contrast, is phrased as a maximum transfer rate (p. 1011), so treat it as an entry requirement rather than a promise.

02.How Long a Burst Takes to Write

Take fifty frames. Nikon's capacity table was compiled on its own 660 GB card with Continuous H (extended) as the release mode, the FX image area, SDR tone mode (standard dynamic range, for ordinary displays) and the electronic shutter. It gives about 17.3 MB for a High efficiency★ raw file and 27.3 MB for a lossless compressed one, and warns that real sizes vary with the scene (pp. 1012-1013). Fifty of the first make $50 \times 17.3 = 865$ MB, and fifty of the second make $50 \times 27.3 = 1365$ MB.

At the V90 floor of 90 MB/s, 865 MB takes $865 / 90 \approx 9.6$ seconds. In general, if $N$ is the number of frames, $s$ the size of one file in megabytes and $w$ the write speed in megabytes per second, the time $t$ in seconds is

$$t = \frac{N s}{w}$$

This is arithmetic, and no camera was timed to produce it. Each cell assumes data reaches the card at exactly that rate throughout, and a real camera must also process every frame, so no row predicts what you will see. Two lessons survive. No SD card can take this burst in under about 2.8 seconds, because the bus forbids it. And a V90 floor and a 260 MB/s ceiling differ by almost a factor of three, which shows how little the "up to" figure tells you.

The CFexpress card has no row on purpose. Its 2,600 MB/s sustained rating would give a third of a second, but in the upper slot the binding limit is, I expect, the camera's own write rate, which the Reference Guide does not state, plus the version limit below. The write time is also your wait before a card swap, since Nikon says to remove a card only once the access lamp is out (p. 96).

Two Copies Move at the Pace of the Slower Card

With Backup, every picture goes to both cards (p. 457), so the SD card must take all 865 MB. That is 9.6 seconds on a card working at the V90 floor and still 2.8 seconds at the bus ceiling, however quickly the CFexpress copy finishes.

With RAW primary - JPEG secondary and a raw-plus-JPEG image quality, the NEF files, Nikon's raw format, go only to the primary card and the JPEGs only to the secondary (p. 457). If each JPEG matches Nikon's 10.3 MB for a JPEG fine at Large size (p. 1012), the SD card receives $50 \times 10.3 = 515$ MB, or $515 / 90 \approx 5.7$ seconds at the V90 floor, about forty per cent less work than Backup with raw alone. Backup with raw plus JPEG would send the SD card both files, $50 \times (17.3 + 10.3) = 1380$ MB.

03.A Faster Card Than the Camera

Nikon's list of cards recommended for raw video, whether N-RAW 12-bit (NEV) files or ProRes RAW HQ 12-bit (MOV), includes one CFexpress 4.0 card, the Nextorage NX-B2PRO series. Its footnote says the card's transfer rates are limited to the speed of the CFexpress 2.0 standard (p. 1011). Lexar's own page on 4.0 cards in cameras describes the same pattern in general terms: a 4.0 card runs at whatever speed the camera supports and reaches full speed only in a 4.0 reader. The footnote names one card, but its reason is the standard rather than the brand, so I read it as covering my Lexar SILVER too.

For video, Nikon asks for 45 MB/s on CFexpress or XQD, written in the old style as 300 since $300 \times 0.15 = 45$, or UHS Speed Class 3 on SD, and 250 MB/s on either side for high frame sizes or rates (p. 1011). Lexar's cards are not on the raw-video list, which matters for the later part on video, and neither SD cards nor XQD cards of 32 GB or less can record N-RAW or ProRes RAW at all (p. 212). Files of 4 GB or more need a card formatted in exFAT, the file system that allows files that large, and Nikon's remedy is one larger than 64 GB formatted in the camera (p. 928).

04.Choosing the Primary Slot

Primary slot selection decides which card receives pictures first whenever both slots hold a card (p. 456). The default is CFexpress/XQD card slot and the alternative is SD card slot. Videos ignore it and follow Destination in the video recording menu (pp. 456, 583).

Keep the default. Under Overflow the primary takes every frame until it fills, and under the split options it takes the raws, so the fast slot should do the heavy writing. An SD primary makes sense only when a job ends with handing a card to someone without a CFexpress reader. Note too that Save/load menu settings saves its file onto whichever card is in the primary slot (p. 860).

05.What the Second Card Does

Secondary slot function sets the second card's job, and its default is Overflow (pp. 446, 457). Of its six options, the JPEG ones work only in SDR tone mode and the HEIF ones only in HLG, the tone mode for high dynamic range displays (pp. 457-458).

Overflow

The second card waits until the primary is full, then takes over (p. 457), and the frame counter shows the card being written at the moment (p. 94). Choose it when running out of space is the bigger danger, as on a long day of bird bursts. The price is one copy of each picture, and SD speed once the camera switches cards.

Backup

Every picture goes to both cards (p. 457). Choose it when the moment cannot be repeated: a dance performed once, a portrait sitting, a landscape three hours' walk from the car. Every burst then waits on the SD card, and with only one card in, Backup makes one copy.

Splitting Raw From JPEG

RAW primary - JPEG secondary sends the NEF to the primary card and the JPEG to the secondary when image quality is set to raw plus JPEG. At any other quality it acts like Backup and records each picture twice at the same setting (p. 457). It suits street work, with shareable JPEGs on the SD card and raws on the fast one. If Multiple exposure or HDR overlay has Save individual pictures (RAW) turned on, those individual NEF files go to both cards along with the JPEG blend (p. 459).

Two JPEGs at Two Sizes

JPEG primary - JPEG secondary writes a JPEG at the menu's quality and size to the primary card, and a JPEG/HEIF basic copy to the secondary at a size you choose by pressing the multi selector right while the option is highlighted (pp. 457-458). With a raw or raw-plus-JPEG quality it equals Backup. For a raw shooter like me it has no role.

The HEIF Pair

RAW primary - HEIF secondary and HEIF primary - HEIF secondary are the same two splits for HLG tone mode, where the camera saves HEIF files in place of JPEGs (p. 458). RAW, JPEG, HEIF and Tone Mode explains what HLG and HEIF are.

When Either Card Fills

With any option other than Overflow, the frame counter reports whichever card has less room, and the shutter locks once either card is full (p. 459). Under Backup, a 512 GB card paired with a 256 GB card makes a 256 GB camera. Under a split, which card fills first depends on the raw compression, the JPEG or HEIF size and quality, and the two cards' capacities.

Deleting a picture held on both cards offers the copy on screen or both (p. 460). Delete pictures from both slots in the playback menu shapes that prompt: Yes (confirmation required), the default, asks, Yes always deletes both copies once you confirm, and No deletes only the one shown (pp. 783, 789). Leave it asking.

06.Which Copy Playback Shows

Dual-format recording PB slot picks the card playback opens on when the two cards hold different versions of a picture, and it applies only to the four split options (p. 790). The default is CFexpress/XQD card slot. Whichever you choose, the playback i menu's Jump to copy on other card shows the partner, and that works for Backup pairs too (pp. 238, 459).

Keep the default. The raw file is the master, so protection and ratings belong on it, and the pages describing these items do not say whether a rating on one copy reaches the other. Choose SD card slot on a street day when you will cull the JPEGs in the camera.

07.Slot Empty Release Lock

Slot empty release lock has two settings. Enable release, the default, fires with no card, records nothing and labels the result Demo in playback. Release locked refuses to fire (pp. 807, 859).

First-Day Setup recommended Release locked, and that stands, but the lock checks only that some card is present. It will not notice a second card left at home on a Backup day, nor an SD card whose write-protect switch is set to lock, which records nothing while the control panel flashes Card (pp. 95, 925-926). Look inside the card door before anything that matters.

08.Folders on the Card

Pictures live in numbered folders, each named with three digits and five characters, NZ6_3 by default, so the first is 100NZ6_3 (pp. 446, 451). A folder is full at 5,000 pictures or a file numbered 9999 (p. 452).

Storage folder chooses where new pictures and videos go, and it is one setting reached from two menus, so a change in either the photo shooting or the video recording menu appears in the other (pp. 451, 581).

• Rename sets the five characters for folders created from now on. Existing folders keep their names, and holding the delete button while the keyboard is showing restores NZ6_3 (p. 451).
• Select folder by number picks a folder by number and creates it if it is missing. Which card receives a new folder depends on Secondary slot function, and icons mark each folder as empty, partly full or full (p. 452).
• Select folder from list picks from the folders already on the card (p. 453).

Renaming is the useful part. Before a recital I would set RECTL with Rename, then open an unused number with Select folder by number, so the recital lands in a new folder such as 101RECTL (pp. 451-452). Playback folder in the playback menu can then show only folders carrying that name (p. 786). Interval-timer, focus-shift and pixel-shift shooting each have a Starting storage folder option that can open a New folder per sequence and Reset file numbering to 0001 with each one (pp. 448-449, 523, 543, 552).

09.File Names

Most files are named with three letters, an underscore, four digits and an extension, so the first raw file from a new camera is DSC_0001.NEF (p. 455). The extension gives the type.

• NEF is a raw photograph.
• JPG is a JPEG, recorded in SDR tone mode.
• HIF is a HEIF, recorded in HLG tone mode.
• NEV, MOV and MP4 are videos.
• NDF is dust-off reference data.

A raw-plus-JPEG pair shares one name, which is how editing software keeps the two together. Adobe RGB pictures move the underscore to the front, as in _DSC0001.JPG, flagging the wider colour space (p. 455).

File naming swaps DSC for three letters of your choice. The photo shooting menu's item names pictures and the video recording menu's names clips, each defaulting to DSC (pp. 455, 578, 582), and Nikon does not describe them as linked the way it does Storage folder, so set both.

Use your initials, so that two cameras on one shoot never both produce a DSC_0412.

10.When the File Numbers Run Out

Four digits give 9,999 names, which a burst shooter can use up in a season. Custom Setting d9, File number sequence, decides what the count does at a new folder or a different card (p. 671).

• On, the default (p. 624), continues from the last number used, keeping names unique across folders and cards.
• Off restarts at 0001 in a new folder or on a fresh card, except that a folder already holding pictures continues from its highest number. Switching to Off stores the On count, and switching back resumes it.
• Reset clears the On count. An empty current folder starts again at 0001, and one with pictures in it continues from its highest number plus one.

Here is On at work. Yesterday's card ended at DSC_8500, and you insert an empty, freshly formatted card and shoot 2,000 frames. The first goes into folder 100 as DSC_8501, and the count climbs to DSC_9999, which accounts for $9999 - 8500 = 1499$ frames. A folder holding file 9999 is full, so the camera creates folder 101 and starts again at DSC_0001 (p. 672). The remaining $2000 - 1499 = 501$ frames become DSC_0001 to DSC_0501. No name repeats on this card, but DSC_0001 now exists twice in your archive, told apart only by folder and date.

When a folder fills, the camera creates one numbered a step higher and switches to it, or takes the lowest free number if that one already exists (p. 672). Folders stop at 999. When folder 999 fills, the camera cannot create another, the shutter stops, and Full flashes in the control panel to say the file numbers are used up (pp. 454, 672, 924). Video stops sooner, once a maximum-length clip would breach those limits (p. 672). To recover, set d9 to Reset and then format the card or insert a new one (p. 672), or use Storage folder to select a folder numbered below 999 (p. 454).

Leave d9 On. Off and Reset tidy one card at the cost of repeated names across many.

11.Copying Between Cards

With two cards in, Copy image(s) in the playback menu copies pictures from one to the other (pp. 800-804, 999). The steps run in this order: Select source, then Select picture(s), then Select destination folder, by number or from a list, and finally Copy picture(s)?. Select picture(s) asks for a source folder and a starting selection, Deselect all, Select all pictures or Select protected pictures. Choosing All pictures in slot instead of a folder skips straight to Copy picture(s)? (p. 801).

Pictures are not copied if the destination card lacks space (p. 804). A name clash offers Replace existing picture, Replace all, Skip or Cancel, and protected files are never replaced. Ratings and protection travel with the copies, and for video Nikon asks for a fully charged battery or mains or USB power (p. 804).

Its best use follows an Overflow day: protect the keepers, then copy them with Select protected pictures, which works one folder at a time (p. 801), so the best frames exist twice before you leave the field.

12.Recommended Settings

For wildlife and birds with the 180-600mm, use Overflow and copy the keepers before formatting. For stage dance, portraits and landscape, use Backup, because none can be repeated. The SD card's pace hardly matters at a sitting or on a tripod. On stage it means waits of nearly ten seconds after a fifty-frame burst at the V90 floor, which I accept for the second copy. For street, use RAW primary - JPEG secondary with the playback slot on SD. Video follows Destination, which First-Day Setup set to the CFexpress card.

13.Beginner Mistakes

Buying by the ceiling. The "up to" figure is the card's best on its maker's bench. Plan with the floor, V90 on SD or a VPG rating on CFexpress.

Paying for CFexpress 4.0 speed in the camera. Nikon limits its one listed 4.0 card to 2.0 speed (p. 1011), and the same limit should apply to any 4.0 card.

Trusting Backup with one card in. The release lock checks only for an empty camera, so a Backup day with one card is a day with one copy.

Leaving the SD write-protect switch locked. The camera records nothing and flashes Card (p. 925).

Turning d9 Off to keep the numbers small. One card looks tidy and the archive fills with repeated names.

Setting File naming in one menu only. Pictures get your initials and clips still say DSC.

14.Related Chapters

• First-Day Setup: inserting and formatting cards, and the first choice of second-slot role.
• RAW, JPEG, HEIF and Tone Mode: raw compression, JPEG and HEIF, and the image quality settings the split options depend on.
• A Tour of the Body: where the card door and the access lamp sit.
• Menus and Controls: finding the photo shooting, playback and setup menus used here.
• Glossary: short definitions of the card and file terms used here.