This gets off the track a bit, but there was a point made earlier in this thread which requires clarification.
The RBA DOES NOT borrow money from commercial banks.
The RBA, like any central bank, is the ultimate source of liquidity for the Australian financial system.
That is, the bank is the ultimate supplier of CASH (liquidity).
Or as some would say, "the lender of last resort".
Or to put it even another way - the RBA is the bank the banks bank with.
The RBA doesn't need to borrow cash from commercial banks - however - banks are required to have funds deposited with the RBA.
These funds are held in what are called "Exchange Settlement Accounts" (ESA's).
For prudential reasons, each licensed commercial bank in Australia is required to keep a certain amount deposited with the RBA - the amount actually changes from day to day.
The bank pays a small amount of interest in return - but this is not how interest rates are set.
At the end of each day there is a great deal of interbank trading whereby one bank owes another money, etc, etc.
The money used to settle these IOU's comes from the ESA's.
As a part of being a bank in Australia you have to pay your dues at the end of each day - using the money deposited in your ESA.
However, the RBA controls the ESA's.
The bank uses this control to implement monetary policy.
To increase interest rates the RBA withholds funds and forces the banks to go into the money market to get the funds they need to pay the daily debts as required. This increases the demand for money in the money market and in doing so the banks bid up the cash rate.
To decrease interest rates the RBA releases more ESA funds than are needed. This will usually mean that the commercial banks will then invest this money in the money market - by increasing the supply of money into that market, interest rates fall.
Apologies for the length.
MB