I've been told that adding additional RAM to a system won't really have any effect unless the current RAM is completely maxed out, is that true? So for instance if a system is at 50% RAM usage with 16GB then adding an additional 16GB won't make a difference?
Correct. However if you sometimes run other programs at the same time, your RAM usage may be higher. Way to know for sure... load up everything you might have running at one time, then check your RAM usage. If that's 50%, adding more RAM won't speed things up for you.
If you have additional unused RAM available, Windows will use that to cache drive sectors. For example, on my system that has quite a few Windows open, the following is shown in task manager: The "Cached" part here refers to various areas of my disk that I have previously accessed (read or written to). Windows will claw this back if programs request RAM, on a least-recently-used basis (i.e. recent access is cached, the oldest is discarded). RAM is an order (or two) of magnitude quicker than SSD drives and probably more for rotational drives. In terms of how this affects traders, this means that any program that reads from the same place on my drive won't actually go to the drive and request the data - it will come straight from RAM. This is a massive performance boost for trading operations involving analyzing large data sets (such as repeated backtesting). For best performance, you should initially ensure you have fast disk (NVME or SATA-based SSD) and sufficient RAM. If you have the budget add more RAM. Both upgrades are relatively minor for a trader and make a world of difference. I regularly deal with 10-15GB data sets, so 32-64GB is a nice place once you add in analysis overheads.
In general that is correct. But most of the current computers use NVME SSD drive, not the traditional rotational mechanical hard drives. Its speed is not close to the DDR RAM speed, but to most people, it is hard to tell the difference. For most people, 16GB RAM is enough, unless you run 3 web browsers, each with 10 pages. Or running several trading apps at the same time with the same computer. But RAM is cheap too. So it is easy to get 32GB or more. When computer runs out of memory, it starts to use part of your SSD HD to swap programs. This was the bottleneck before the NVME SSD era. Now it is not very noticeable with the performance degrade. If you ever suspect that you need more RAM, just go out to get it. You can easily support that with one day's trading profit.
Thanks everyone for the replies, really appreciate it. I'm mainly asking because I'm in the process of brainstorming a new system and I'm trying to decide of what's needed/not needed etc. I only use my computer for trading (running esignal and broker platform) + basic web browsing, my 16GB of RAM has been running at about 50% (this is on an older 4790cpu - DDR3), so based on that I am kinda sorta thinking that I don't really need any more than 16GB of DDR4 in the new system. (?)
If you're only using 50%, then you can probably get by with 16 GB. If you do that, order a configuration that will allow you to easily upgrade to 32 GB if needed in a few years. If it's not much, might as well go with 32 GB now and save yourself the upgrade later.
This blog post about trading computers is from 2020, but I suspect that some of the more general concepts about RAM still apply: https://orbitalcomputers.com/trading-computer-buyers-guide-2020-update/ (Note: Not a recommendation for the company, and not affiliated with them in any way.)
If you want to economize, you could get a fully competent trading workstation (used) for ~$250-$400. (When I do a big upgrade of my hardware, I buy 6 machines. Buying used saves several $thousand.)