These TPM libraries are sometimes also called TPM stacks, because they provide the interface for the developer or user to interact with the TPM. As seen from the table, the TPM stacks abstract the operating system and transport layer, so the user could migrate one application between platforms. For example, by using TPM stack API the user would interact the same way with a TPM, regardless if the physical chip is connected over SPI, I2C or LPC interface to the Host system.