When you enter data and you want to save a file, the SED encrypts the data but where does the encryption process occur to be exact? Does SED encrypt data in memory before it gets to the disk? Or do they re-encrypt a block or page on SSD once the writing is done?
The encryption process takes place in the embedded processor on the SSD. Consequently, it's in the computer's RAM and the SATA (or PCIe) bus in plaintext, then copied to RAM on the SSD, encrypted, and written out to a flash block. The unencrypted plaintext should never hit the flash of the SSD.