Do you have an idea of the maximum number of symbol (or entry) that we can add in the Quote Monitor screen ?

There is no such tool as Quote Monitor, but there are Quotes windows and the Strategy Monitor. I guess a number of factors influence the maximum number of streaming symbols across Quotes windows:

1. If your current streaming subscription covers 500 tickers (take IQFeed for example), this is the cap.
2. Available RAM and PC performance
3. Network connection throughput (rarely the bottleneck these days)

But based on what Robert previously said w.r.t. his Fidelity streaming feed experience, I guess that thousands of symbols shouldn't be a problem.

Thank you ! My subscription can allow me 1000 tickers. As I have 10 alerts by tickers, do you think that I can run Quote Monitor without problem with a 32 Bits version (4 Gb of memory) ?

I'll leave the answer up to Robert who's the expert here.

Note that even if your operating system is 64-bit, a 32-bit process like WL6 x86 is still limited to the same constraints: a 32-bit application's virtual address space is only 2 Gb (or maybe 3Gb if WL6 x86 is compiled with LARGEADDRESSAWARE flag enabled, of which I'm unsure).

Memory isn't an issue with the number of streaming quotes... the main factors are the processor, "ticks", and optimizations in the streaming provider code. In other words, there's a big difference in processing 1000 symbols that have an average of 100 trades per minute and an average of 10,000 trades per minute.

In my experience, Wealth-Lab Pro with the Fidelity provider has no problem with the Russell 3000 in the Quotes tool using a modern processor.

Thank you for your reply. If I understand, as ticks are requested per symbol (and not per alert), I can expect to work with several alert (around 10) for 1000 symbols without problem. Is it right ?

QUOTE:
as ticks are requested per symbol (and not per alert)

Right, ticks are requested per symbol, and the Quotes subsystem is smart enough to not fire duplicating requests (e.g. if one symbol exists across several Quotes windows).