In modern retail, most of the time taken to process a transaction is independent of the point of sale software.
If you think about it, every customer when being processed today should be greeted with a friendly smile, hellos exchanged, they are processed, the cash or EFTPOS is handled, goodbyes are said, and they go. The industry standard to do this is about 40 seconds a transaction plus about three seconds for each item to scanned and rung up. So if they want to buy four things, the time taken is expected to be about 40 seconds plus four items in their basket at 3 seconds each so its about 52 seconds.
Very little of this time is actually due to the POS software slowing down the transaction.
Of course, the trouble that retailers have is if the queues start to get big, then people walk out. What annoys retailers is when they see people dumping their proposed purchases and leave. What is even worse people then often avoid shops that they know has long queues and do not come back. So they hellos and goodbyes get a bit quicker, the processing gets rushed.
To see what is happening now with our system, I took about 20,000 cash register transactions from a client with actually a slow machine but in a busy shop and measured their results.
The average speed of a transaction was about 36 seconds a sale which is what I expected as our clients tend to have low numbers in their baskets and they are almost all in high volume pressure environments.
Here is what the graph looks like
As you can see in a pinch, our clients are doing transactions much less than 36 seconds as you can see here in seconds.
So it is not the computer, but on an average, I think our clients should budget about 36 seconds plus or minus.
One idea that does work well in practice is to introduce a single queue, and have many cash register serving that queue. Although there are still waiting, people do prefer it. If you have access to Mythbusters shows checkout S16E05 which has an experiment on this, the conclusion was even if this method is slower, people prefer it as it appears fairer. For a discussion on the subject click here,