По первой спецификации все обязаны поддерживать блоки в 512 байт:
Цитата
It is a mandatory requirement that SD Memory Card shall have a capability to transfer blocks of 512 Bytes.
...
A card supporting block write shall always be able to accept a block of data defined by WRITE_BL_LEN and its
512bytes derivatives (for example: If write block length=1024bytes then write blocks of 1024 and 512bytes are supported).
Во второй спецификации размер блока строго фиксирован на 512.