how does a bitcoin exchange works ? ex coinbase

[anorphirith]

I've been trying to figure out how bitcoin exchange services work. Specifically the ones that allow you to exchange btc for fiat money and viceversa.

for example

If I try to buy 2 bitcoin:
1-are they going to give me a coin that they already have ? or
2-are they going to give me a coin that a seller is trying to sell ?

if they give me a coin they already have, how do they now they'll always have enough to supply all the buyers ?
if they give me a coin that a seller is trying to sell, how to they know that they will always have enough volume to satisfy all the transactions ?

finally is this entire thing managed by some type of database, oracle? sql ?

thanks !

[Kazimir]

I've been trying to figure out how bitcoin exchange services work. Specifically the ones that allow you to exchange btc for fiat money and viceversa.[/q]
They allow people to send money (both BTC and fiat) to them. Then they allow people to buy bitcoins with fiat (if they have deposited enough fiat) from other people who want to buy fiat with bitcoins (if they have deposited enough bitcoins).

Exchanges don't actually buy or sell fiat or bitcoins themselves, they're just a marketplace who brings together people who want to trade. That's the service that the exchange "sells", and for which they charge a commission fee.

[anorphirith]

ok thanks for the reply,
but at the beginning of coinbase for example,
how did they gather enough buyers and sellers to make the transactions ?
is that what the 4 days delay was for (besides the ACH approval)  ?

what happens if
one guy is selling btc4.235 at $840 and another guy is selling btc6.135 at $735
while a buyer i buying btc2.435 at $751 and another buyer is buying btc7.139 at $813
since the price is so volatile almost all transaction will be made at different prices, how is it possible to match up buyers and sellers ?

[LakeBTC]

ok thanks for the reply,
but at the beginning of coinbase for example,
how did they gather enough buyers and sellers to make the transactions ?
is that what the 4 days delay was for (besides the ACH approval)  ?

what happens if
one guy is selling btc4.235 at $840 and another guy is selling btc6.135 at $735
while a buyer i buying btc2.435 at $751 and another buyer is buying btc7.139 at $813
since the price is so volatile almost all transaction will be made at different prices, how is it possible to match up buyers and sellers ?

coinbase is not an exchange. it's more like a dealer.

we are an exchange, supporting both USD and CNY for the time being.

check it out LakeBTC.com