SD Card File System

[steeley7]

Using Dane Elec 256 XD card with tom tom nav 3 ...what file system should I use on it FAT16 FAT32 etc and what cluster size should I use.. I'm using storage tools to do the job

[Hunnymonster]

It depends on your hardware, and the mix of files you're likely to store on it:

FAT32 with a small cluster size means a bigger FAT is required, but you have less slack space.
FAT32 with a large cluster size means a smaller FAT is required, but you have more slack space.

Er.... ok what does that mean ?

If you format with a cluster size of 4k, it means that each file is recorded in the FAT in blocks of 4k, and for example a 10k file will consume 3 blocks - and have 3 cluster entries in the FAT. It will waste 2k of the 3rd block in doing so.

If you format with a cluster size of 32k, it means that each file is recorded in the FAT in blocks of 32k, and for example the same 10k file will consume 1 block - and have only 1 cluster entry in the FAT. It will waste 22k of the block in doing so.

Turning that example into a 4Mb file means that in case 1 you'll have 1024 entries, and in case 2 just 128.... and on average with every file you waste half a cluster - so lots of little file means small cluster good, big files means large cluster good.

Of course this is just looking at it from a raw filespace viewpoint - performance also varies.... but it's probably not as easy to explain as it's hardware dependant as well.

Although seeking 128 clusters ought to be swifter than seeking 1024 - the data read overhead may obscure that small but visible difference....

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