The ISD-300A1 was designed to the ATA/ATAPI-5 specification, which has 28 bit LBA addressing. This equates to 268435455 LBAs. Assuming 512 byte sectors this is 137,438,952,960 bytes. After formatting the user will get 128GB of usable disk space. Cypress recommends the EZ-USB AT2 (CY7C68300), CY4611 rev C or the CY7C68310 for designs with larger disk drives. These devices were designed to the ATA/ATAPI-6 specification, which has 48 bit LBA addressing and overcomes this limitation. The limit for ATA-6 is approximately 144 peta bytes.