Because of the sector based error correction. I remember some earlier 8-bit disks has 128 byte sectors. Some newer flash SSDs have 1k-4k physical sector size fo

Because of the sector based error correction. I remember some earlier 8-bit disks has 128 byte sectors. Some newer flash SSDs have 1k-4k physical sector size for ecc coding efficiency so in those cases they will internally do a read-modify-write to handle a 512 byte logical sector size.