SD card RAM doubt

[redsuns]

why a sd card have to use microcontroller with RAM more than 512kb?
what will happen if i use sd card with a uC RAM lower than 512?

 

[dougy83]

The sector size used to be 512bytes (may have increased, I'm not sure). So this means it is easier to read and write if you have more that 512 bytes. You can function with <512b; but it will be difficult and limited (e.g. reading/writing contiguous bytes is possible, but a file system may not be).

 

[mneary]

Are you sure you need 512 kilo bits? Seems like a lot for a microcontroller, and an unusual way to express it. You would need an external RAM for most devices that I know. That would be more commonly expressed as 64 kilo Bytes.

Maybe you could post your reference; we can only guess unless we know more about the design.

 

[DirtyLude]

Like dougy83 surmised, I think he means 512bytes. The block size is 512 bytes and anything less means you can only write partial blocks to the card. You can deal with that if you aren't using a file system and don't care about a bit of wasted space, but if you are trying to implement a file system you need to be able to write full blocks to the card.

 

[mneary]

512 bytes is not an outrageous requirement, I just can't see why OP would question it. On the contrary, I would think it to be too small.

 

[DirtyLude]

I think he is questioning it because he misinterpreted 512b as 512kb. Obviously 512kb is way off the scale. 512b is the minimum for the write buffer, but clearly there is some other overhead for other variables you are using.