There are cards and cards. I started testing my own card speeds ages ago. It's not just the size capacity that's important but the read and write speeds. When your system boots the first thing it does is read the file tables. The bigger the catalogue, the longer it takes to read it and transfer data to memory inside the media player. If the track titles are used for the filenames, these can run to many characters, all data in the file allocation table that has to be stored, searched and read.

Most media players in cars are well behind on processing power, probably using RISK ARM on a Win CE Mobile operating system. Android is a little too modern for many car systems. Aftermarket car systems tend to be WINCE or open source Linux based. Commonly 650 Mhz or 1Ghz if you are lucky. When choosing a card, look at the read/write speeds. But watch out for Ebay cards even those appearing branded. I've had some running at 1/4 the manufacturers spec. which I concluded were fake. Even though you pay more for a faster card, there is no guarantee your media player IO will take full advantage of it.

I buy SDHC cards for my camera and I can only get the fast multi shot speeds from the camera with X10 or faster cards. I tend to buy Transcend. All SD cards have their own processor to manage the card content unlike compact flash cards which were just memory. Compatibility issues do arise because the SD card processor has to translate data read and write requests from the host device.

There are some tricks you can play with these cards. When you keep dumping music tracks on to a card or bulk copy, they don't always get stored in the most efficient way for search and retrieval. There's software that will re-assemble your card catalogue in the most efficient way for reading if it's a card you don't want to keep adding new music to.

 

SDHC format standard is up to 32Gb. Cards larger than 32Gb are SDXC (Secure Digital Extended Capacity). Each are different formats and require the device to understand them. VW radios should say what card formats are supported in their specs.

Compatibility is backwards not forwards. i.e SD and SDHC cards can be used in players reading SDXC, but SDXC cannot be read in a SDHC compatible player. People with older smartphones have been finding the same problem. Trying to read SDXC cards on an incompatible system is like trying to read a 3 1/2" floppy in a 5 1/4" drive!!

If you are looking for a car media player that handles new card formats it is unlikely to come from a car manufacturer and any firmware updates will be slow to arrive. I had a friend with a new French brand car with built in satnav that couldn't handle UK post codes. After many broken dealer promises they sold the car after a year. 3rd party non-oem Chinese units may not be perfect, but with short product development times and open operating systems, they are likely to be more up to date with present, emerging and changing digital standards.

As an example of how you can be misled, here is a short video link reformatting a 64Gb ExFat card to FAT32. Theoretically this cannot be done so where's the catch? I tried this once and whilst the card may report its size in the header as 64Gb after re-formatting, you can only store 32Gb of data. The guy who posted the vid. hasn't tried putting 64Gb of data on his reformatted card! Why would you buy an expensive 64Gb SDXC card only to use 32Gb of it?

https://www.youtube.com/watch?v=JA9fp863d-o

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