I checked traderbot website and it is an interesting service but not exactly what I want. However it takes all computation burden on the server side which greatly limits how flexible and powerful a screener can be. With the increasing computational power of our Pcs and the shift to broadband service, it might be a better architecture to let the client side to do the screening while the server side only provides some continuous screaming of AGGREGATED data (and/or with some value add-in indicators like the buy/sell presure on traderbot), but definitely not necessarily to be tick by tick data, because such kind of data service would be provided specificly for screening over broad market in quasi-realtime, instead of for realtime charting, level II quoting, or automatic trading purpose. In the later category, esignal, qcharts etc are the example. However to download tick by tick data of all stocks in realtime is impossible for personal users (esignal normally limit the symbols to 500). Moreover for screening purpose, I am really not willing to pay for all other bells and whistles coming with those data service like esignal or qcharts. (although I have been an esignal users for two years).
Back to traderbot, the possible screeners are greatly limited because it lacks the feature of screening based on user's scripting. One website which supports user screipts is stockfetcher, although there is still a lot of limitation on stockfetcher. Therefore the more flexible and powerful way to do quasi-realtime screening is to do it on the client side with software written from scratch, which not only supports simutaneous screening and realtime alert based on multiple strategies, but also can evaluate the market condiftion in realtime to decide which screening script to use. However to achieve this in my mind, I need the data service first.
In my previous post, the 100 bytes is refer to the estimated number of bytes needed to transmit for EACH SYMBOL EACH UPDATE PERIOD. Suppose we need to track 10000 symbols and each symbol needs 100 bytes and the update period is 2 minute, it is roughly about 70Kbps ( 8 bits/byte * 100 bytes * 10000 / 120 second ~ 70Kbps ), which is really not very bandwidth consuming.