Purchase ledger & sales ledger

Hi,

In F3, we learned books of prime entry and receivables ledger and payables ledger.
In F8, sales ledger and purchase ledger are used quite often when talking about substantive procedures. For whatever reasons, neither BPP F3 course notes nor OT F3 course notes introduce them.

Some articles on the internet say sales ledger = receivables ledger & purchase ledger = payables ledger. Some say sales & purchase ledger simply record all the sales and purchases.

What really do purchase ledger and sales ledger record? Thank you very much.

Emma