I decided to break this out of another thread I had since it fits here and is semi useful to people planning on buying a computer just for trading with MT4:
Now I do suggest investing in a decent (read: stable and well supported by the manufacturer) system that will allow you to run more intensive software than Metatrader 4, but if all you need is MT4 and don't want to spend a lot, then the quote above will help. A decent box for just MT4 can be had for under a hundred bucks these days if you pick up an off-lease business-level desktop from a refurb company.MT4 is old as dirt.. pushing past 10 years now.
It's strictly 32bit. It can't make use of more than 2Gb of RAM, single threaded, and it doesn't handle well on Windows Vista and beyond.
It also can't make use of a lot of the newer hardware assisted math functions found in some processors... nor have I seen anyone putting out a version that can take advantage of GPU computing to speed backtesting up.
Basically, it's dated.
So I found for the best possible experience (speed wise,) for MT4 backtesting, start by setting up a system with a higher clock rate, higher cache, dual core (not quad or greater) processor. You don't even need dual core, but it's not like you can find single core processors these days and at least the 2nd core means you can browse the net without it feeling sluggish as your MT4 works away on a backtest.
Run 32bit Windows XP... actually, I've been told by a very high up person at a brokerage (who knows his way around IT stuff) that the best OS for MT4 (stability and speed wise) was Windows 2000..
64bit Windows has to run MT4 in WOW mode, that's Windows-on-Windows... it's a compatibility layer and it slows the kinda processing MT4 does during backtesting down quite a bit.
Don't worry about RAM greater than 3-4Gb. More is just not needed (OS won't use it, MT4 won't use it.)
Just a few thoughts if you ever are building out a system specifically for MT4 backtesting. You won't be future proofing yourself going this way, but at least MT4 will run like a dream.