This software development works started from Metatrader 3 and MT4 was eventually released in 2005. It comes with client terminal, Mobile, server and data center manager. The widely used platform on PC is the Metatrader 4 client terminal.
This software which are installed on windows operating system comes with real time data feed from brokerage server, able to demo trade and perform strategy analysis using strategy tester. It also comes with various trade operations (Buy, sell, stoploss, profit take, lot size, etc) and technical charting (indicator like SMA, CCI, RSI, etc). One of the key feature is the programming language (similar to C language) MQL that allow traders to program their strategy into computer program call expert advisor.
Expert Advisor (EA)
This is a program which can be compiled to run on MT4 as a standalone automated trading program. The EA is coded entirely using MQL4 languages and compiled debug using editor. Recent advancement in computer coding has enable multi-currency trading, hedging and signal mirroring to be programmed into a signal programming code software.
What if I have more then 1 account?
The problem surface when you are running more then 1 trading account which is often the case when you are running many demo account to tried out many Expert Advisor. As MT4 installation registered inside windows registry but it did not allocated shared resources for multi software running on the same operating system. In other words, you can copy the whole MT4 program folder and paste into another directory, and execute the terminal.exe. The window will treat this as a separate software and allocated individual resources to it. This is similar to running 2 copies of the software. Using this loophole, you can easily run 6 or 8 MT4 software with different trading accounts on a same PC.
VPS and shared dedicated server
I used the above trick and run 7 trading account on 7 separate metatrader4 software on VPS and shared dedicated server and found it to be running smoothly. The windows 2008 server operating system see each software as an entity and allocate individual resource to run it. Personally, I can run multiple account and charge trader usage of my Expert advisor including server maintenance fees. Am using build 209 at that time.
Multiple window login using background services
I never tried before but heard that if you enable back ground multitasking services and multi user login on linux platform which you can log in simultaneous using 2 or 3 user and run programs, you can effectively be running 7 programs x 3 users, total 21 trading account. If you charge a trade a fees for running expert advisor on their trading account, you have potentially 21 trading account you can load on to your VPS server.
Lastly, if you are running VPS or shared dedicated server, always setup auto-logging and auto-starting the MT4 program. I personally setup this way as when there is server reboot or unexpected power outage, when the power resume, upon server startup, will perform auto login and the program will automatically start and carry on the last trade order. This is just a trick that you need to know.