not support a 4 GB SDSC card, since the specification lets it assume that 2 GB is the maximum for these cards. Storage capacity calculations The format of the Card-Specific Data (CSD) register changed between version 1 (SDSC) and version 2.0 (which defines SDHC and SDXC). Version 1 In version 1 of the SD specification, capacities up to 2 GB are calculated by combining fields of the CSD as follows: Capacity = (C_SIZE + 1) × 2(C_SIZE_MULT + READ_BL_LEN + 2) where 0 ≤ C_SIZE ≤ 4095, 0 ≤ C_SIZE_MULT ≤ 7, READ_BL_LEN is 9 (for 512 bytes/sector) or 10 (for 1024 bytes/sector) Later versions state (at Section 4.3.2) that a 2 GB SDSC card shall set its READ_BL_LEN (and WRITE_BL_LEN) to indicate 1024 bytes, so that the above computation correctly reports the card's capacity; but that, for consistency, the host device shall not request (by CMD16) block lengths over 512 B. Versions 2 and 3 In the definition of SDHC cards in version 2.0, the C_SIZE portion of the CSD is 22 bits and it indicates the memory size in multiples of 512 KB (the C_SIZE_MULT field is removed and READ_BL_LEN is no longer used to compute capacity). Two bits that were formerly reserved now identify the card family: 0 is SDSC; 1 is SDHC or SDXC; 2 and 3 are reserved. Because of these redefinitions, older host devices do not correctly identify SDHC or SDXC cards nor their correct capacity. SDHC cards are restricted to reporting a capacity not over 32 GB. SDXC cards are allowed to use all 22 bits of the C_SIZE field. An SDHC card that did so (reported C_SIZE > 65,375 to indicate a capacity of over 32 GB) would violate the specification. A host device that relied on C_SIZE rather than the specification to determine the card's maximum capacity might support such a card, but the card might fail in other SDHC-compatible host devices. Capacity is calculated thus: Capacity = (C_SIZE + 1) × 524288 where for SDHC 4112 ≤ C_SIZE ≤ 65375 ≈2 GB ≤ Capacity ≤ ≈32 GB where for SDXC 65535 ≤ C_SIZE ≈32 GB ≤ Capacity ≤ 2 TB Capacities above 4 GB can only be achieved by following version 2.0 or later versions. In addition, capacities equal to 4 GB must also do so to guarantee compatibility. Openness of specification Like most memory card formats, SD is covered