OK so as a none techie why is it not genuinely instant? Why can't my cash be exchanged for the stock in real time (where real time is defined as within a minute or two say).
It's cheaper to do it slower - banks don't have to constantly talk to each other all day. Russia actually gave up on same day settlement and called it a modernization.
When I left Australia in 2006, inter bank transfers settled every four hours. Often by ISDN lines between banks. "Constantly talking" is a BS excuse. As far as I know (someone still there can correct me) inter bank transfers there are now down to 5 minutes.
The US banking system is arcane and archaic. It's cheaper not to modernize to be sure. Forgive me for being frustrated at banks cheaping out on this when they average quarter of a trillion dollars in profit every year over the last few years.
Yep, in Europe inter-bank transfers are also instant and if the underlying reason for all these regulations, confusions and trading impact is that US institutions have just been too cheap to upgrade the legacy infrastructure running the biggest store and exchange of value in the world then frankly surprise and anger seems justified.
https://www.fintechfutures.com/2013/03/moscow-exchange-adopt...
Also, you may still be able to pay for stocks with checks at some places, so the cash isn't always available.