Sony a1 Memory Card Guide: Dual Slots, CFexpress A & 8K Specs

Sony’s flagship Alpha 1 (variously known as the a1, α1, or ILCE – 1) remains a high-water mark for hybrid performance.

With a 50.1MP sensor capable of 30 fps bursts and high-bitrate 8K video, the camera generates a staggering amount of data. To keep the hardware and post-processing workflow moving smoothly, selecting the right media is about removing bottlenecks rather than just finding “compatible” storage.

The Sony a1 features two identical hybrid memory card slots. Each slot is a mechanical marvel that accepts either a CFexpress Type A card or a standard SDXC card. You don’t have to choose one format for the whole camera; the design allows you to mix a CFexpress A in Slot 1 for absolute speed and a high-capacity SDXC in Slot 2 for an inexpensive backup.

Sony a1 compatibility & requirements

Unlike some cameras that force you to use one of each type, the a1 gives you total flexibility. You do not need to have both slots filled for the camera to work.

However, filling both allows you to control how files are managed in the field. You can have images saved to one card and video to another, or save duplicates simultaneously to create an instant backup — an essential configuration for client work.

But the different card formats aren’t the same in performance. When choosing which format to use, the rule of thumb is simple: choose CFexpress A cards for maximum performance and buffer clearance, and use SD cards for convenience, cost, and larger storage capacities.

CFexpress Type A cards for the a1: 2.0 vs 4.0

CFexpress Type A is one of the three form factors released by the CompactFlash Association. While the physically larger Type B cards are more common in Nikon and Canon flagships, Sony has prioritized the smaller Type A format to keep their camera bodies incredibly compact. Note that they are not interchangeable; a CFexpress Type B card simply won’t fit in the a1’s slots.

For slow-motion S&Q recording, the camera requires a CFexpress Type A card rated VPG200 or higher (Video Performance Guarantee), which is Sony’s way of saying the card has to guarantee a sustained write speed, not just a fast headline number. It’s worth knowing that this is a slow-motion requirement rather than an 8K one — slow-motion and quick-motion recording aren’t available in XAVC HS 8K at all.

Should you buy a CFexpress 4.0 card for the a1?

The CFexpress Type A market is currently transitioning from the older 2.0 spec to the newer, twice-as-fast 4.0 spec. Because the cards look identical, navigating this shift is an excellent opportunity to save money if you know what to look for.

The Sony a1 is a CFexpress 2.0 camera. It physically lacks the internal hardware required to hit the newer 4.0 speeds. However, because the standard is perfectly backward compatible, you can put a bleeding-edge 4.0 card into the a1, and it will work flawlessly (throttled to 2.0 speeds by the camera).

Because manufacturers are aggressively changing their production lines to the new standard, newer 4.0 cards are sometimes actually cheaper and more readily available than the legacy 2.0 cards they replaced. In a market distortion due to algorithmic pricing based on limited legacy stock, older 2.0 cards frequently show up at massively inflated prices.

The rule of thumb is to look at the sustained write speeds and go with whatever is cheaper, regardless of whether the label says 2.0 or 4.0. If you spot a 4.0 card for the same price or cheaper than its 2.0 equivalent, grabbing the newer version is a fantastic win. You keep extra money in your pocket today, and you unlock drastically faster desktop offload speeds when you get back to your desk (provided you pair it with a USB4 reader, like Sony’s MRW-G3, rather than a 10 Gbps one that caps out around 1,000 MB/s).

Here are the most reliable CFexpress Type A options for the a1. They easily sustain the required write speeds to clear the a1’s 30 fps buffer and high-bitrate video modes:

SDXC (UHS-II)

SD cards remain the most cost-effective way to get large storage capacities. The current range goes well beyond 1TB, which is helpful when dealing with the a1’s 50MP files.

The downside is the interface speed. Even the fastest UHS-II SD cards peak around 300 MB/s, whereas CFexpress A cards can sustain 700 – 800 MB/s. For casual stills, you won’t notice much difference. However, if you are shooting 30 fps bursts or high-bitrate video, the SD card will cause the buffer to fill faster and clear much slower, which creates immediate friction in the field.

When using SD cards, I highly recommend sticking to SDXC (64GB and larger) because they use the modern exFAT filesystem, which is better suited for large continuous video files¹). To ensure your buffer clears as fast as the SD standard physically allows, buy a V90 UHS-II card.

Tip: Avoid SD Express or SDUC cards. The a1 lacks the internal hardware to interface with these standards. While SD Express cards are technically backward compatible, they will default to much slower UHS-I speeds, wasting your money.

I maintain a detailed breakdown of the fastest SD cards here based on independent testing, but these are excellent choices for the a1:

The dual-slot bottleneck trap

Because the a1 allows you to mix and match formats, you have to be extremely careful about how you configure the camera’s dual-slot behavior in the menu.

If you put a lightning-fast CFexpress Type A card in Slot 1 and a standard SD card in Slot 2, and then configure the camera to shoot in Backup Mode (writing duplicate RAW files to both cards simultaneously as a fail-safe), the camera’s processor cannot clear its internal buffer until the file is written to both locations.

Because the SD card is physically much slower than the CFexpress card, the entire camera will instantly bottleneck to the speed of the SD card. If you are shooting a 30 fps burst, the camera will stall out rapidly. To avoid this, configure the slots to RAW / JPEG (sending the massive RAW to the CFexpress card and a lightweight JPEG to the SD card) or use Slot 2 strictly as an overflow drive.

The golden rule: Formatting & card prep

The golden rule for storage media is to always format the memory card directly inside the camera before a shoot, rather than relying on your computer to do it. You can format either slot by navigating to the yellow Setup Menu (Toolbox Icon) > Media > Format. Be sure to select the correct slot before confirming.

If you accidentally format the wrong card, stop shooting immediately and pull the card from the camera. Because the camera performs a high-level format that only wipes the directory index, you can usually recover your deleted photos using a desktop recovery tool as long as no new data was written to the card.

If your memory card begins to act sluggishly or throws read errors after months of heavy use, a standard in-camera format might not be enough. In that case, connect the card to your computer and execute a full format instead of a quick format using a dedicated utility tool to deeply restore the flash memory.

CFexpress Type A card readers for the a1

This is a common point of friction for first-time Sony flagship buyers: while the physical sizes are similar, your old SD-only reader cannot read a CFexpress A card. To bridge the gap to your computer, you will need a dedicated reader with internal hardware that explicitly supports the CFexpress A interface.

Sony makes a solid single-slot reader (MRW-G3), but there are now excellent dual-slot options from ProGrade Digital and Lexar that can read both a CFexpress A card and a UHS-II SD card seamlessly. This is a massive time-saver when offloading a long day’s shoot to your computer.

If your kit also includes a Nikon Z9, a Canon R5, or anything else built around CFexpress Type B, don’t assume one reader will cover everything. Type A and Type B are different form factors with different connectors, so a Type A slot won’t take a Type B card and a Type B slot won’t take a Type A card. In practice that means either two readers or a unit whose spec sheet explicitly lists both a Type A and a Type B slot — check the slot list, not just the word “CFexpress” on the box.

In my own workflow, I’ve also been using the new PGYTECH dual-slot reader. It acts as a rugged storage case, handles the heat of long transfers well, and provides a stable connection for both slots. You can find my full review of the PGYTECH reader here.

Notes & References:

1. SD Association specifications: SDHC is 4GB to 32GB (FAT32), while SDXC is 64GB to 2TB (exFAT [↩︎]