What is the difference between attachment and perfection of a security interest under the PPSA?

Attachment is the point at which a security interest becomes enforceable between the lender and the debtor — generally once there's a valid security agreement, the lender has given value, and the debtor has rights in the collateral. At that point the lender has a real, legally enforceable interest in the collateral as against the debtor, even if nobody else knows about it yet.

Perfection is the further step needed to make that security interest effective against third parties, not just the debtor — typically by registering a financing statement in the PPSA registry, though for some collateral types perfection can instead be achieved by taking possession or control of the collateral. A security interest can attach without ever being perfected, but an unperfected interest is significantly weaker: it's generally vulnerable to being outranked by other creditors who do register, and it's typically treated as unenforceable against a bankruptcy trustee if the corporation becomes insolvent. In practical terms, attachment gives the lender a claim against the borrower; perfection is what protects that claim against everyone else, which is why lenders treat prompt registration as essential, not optional.