System Building 101 - Memory

Want to know how to pick correct memory for your system? How much memory do you need? How much is too much? How fast does it have to be? All these questions and more are answered in this guide.

System Building 101 – 9 Part series

In this 9-part series we’re going to cover all the major aspects of building a custom PC. We at AVADirect have been building custom PCs for over 10 years and have plenty of experience in building rock solid, custom computer systems. This guide will allow us to share some of that experience with you to make your custom PC building as easy as possible.

In the last part, we talked about motherboards and how to choose between different chipsets. In this section, we will focus on memory, explain the basics and help you determine which memory is best for your system.

Current Market

At the moment, there are many memory manufacturers that make Desktop, Laptop and Server memory. Some of the most popular ones that we frequently use are Kingston, G-Skill, Corsair and Patriot. While there are many others, these 4 provide some of the best memory you can buy for your system. If you have brand preference, you can pick any one you like, as brand is not as important as much as the specifications of memory modules. However, the brands we recommended above are a good starting point if you’ve never shopped for memory before.

Important Classifications

Before we begin talking about specific memory properties, some of the major ones include the standard or type. Just like CPU’s come in different sockets, memory modules come in different standards. For example, you can have DDR, DDR2 or DDR3 memory. They are not cross-compatible with one another. Your choice of motherboard will dictate the type and capacity of the memory you should buy. DDR 3 is the most recent memory standard and is currently offered on all brand new models of motherboards. If by any chance you’re buying a motherboard that supports older, DDR2 standard, then make sure you get the DDR2 memory.

Capacity and Speed

Each stick of memory is called a module. A kit of memory is typically 2 or more modules. Therefore if you see something like a 2x8GB, this is a 16GB memory kit. Why? Because there are 2 modules, each having 8GB capacity. When it comes to finding the right kit for you, there are some limitations.

1.      You can only install same number of modules as there are slots on the motherboard. If the motherboard has 4 slots, you can install up to 4 memory modules.

2.      You cannot exceed capacity per module over what the motherboard specifies. For example, if motherboard has a 4GB per module limit, you cannot by 8GB modules, they will not work.

As for the performance specifications of memory, there are several items to look at:

1.      Speed, usually expressed in Mhz.

2.      Timing, usually referred to as CAS, but more on this later

3.      Voltage,

Memory speed for most DDR3 modules ranges between 1066MHz and goes up over 2100MHz. CPU manufacturers will often list maximum supported memory speeds on the product page. For example, 2nd generation Intel sandybridge CPUs had maximum supported memory speed of 1333MHz. Current generation (3rd) has maximum supported memory speed of 1600MHz.

What does this mean? In order to receive support from CPU manufacturer, you need to run the maximum advertised speed. Can you run higher? Absolutely, but you will not receive support from that CPU manufacturer until the memory speed is configured correctly.

General rule of thumb to follow is that if you’re not planning to overclock memory, then sticking with the maximum supported memory speed set forth by CPU Manufacturer is the best idea. Speeds such as 1866MHz and higher are not needed unless overclocking is involved and will not give you extra performance unless utilized properly.

Of course this only applies to the time of this guide. In the future, 1866Mhz may be the standard memory speed and would make sense to go for it.

Highly Technical Bits

As for timing, it can get very complex to understand, which is why manufacturers typically list the memory timing as just CAS 9 or something like 9-9-9-27. CAS 9 is the memory latency, and is the first number in the sequence of 9-9-9-27. In other words, 4 primary timing properties of memory are listed in a row such as 9-9-9-27. Memory timings can be very complicated to understand, especially when you get into the full list, but all you have to know is that in most real time applications, they don’t exactly make a huge difference.

When ran through benchmark tests, faster memory timings will show increased performance, but the increase is so minimal that for majority of PC users it simply isn’t worth bothering with the timings as they are mostly oriented towards overclockers.

Last bit of information you want to know about is the voltage. This is basically manufacturer recommended setting at which you should configure your modules. Leaving your BIOS settings on the motherboard to AUTO will typically get the correct voltage, but if you like to be precise, you can always manually force the correct DRAM voltage through BIOS.



While the section above may have made your head hurt a little, we want you to know that you don’t need to overthink this too much. Simply focus on how much memory you want, pick the highest speed supported by CPU manufacturer, and you’re on your way. The specific settings are there for those who want the extra tweaking capabilities, but they are by no means necessary for daily operations. We at AVADirect do the rest of the work for you and focus on the technical bits, while all you have to worry about is just how much memory is enough.


A lot of our customers typically ask us “How much memory should I get?” The most obvious answer is: as much as your motherboard supports. However, this isn’t always ideal and your budget might not allow for such an upgrade. If that’s the case, here are some figures that should clear things up:

1.      We live in a 64-bit world now, so having at least 4GB of RAM is highly recommended

2.      Because RAM is upgraded in pairs, if you wanted to have just a bit more than the minimum requirement, opting for 8GB of RAM is probably your best bet and would put you in a sweet spot.

3.      16GB of RAM or more is only necessary if you know you’ll be using memory hungry applications such as Video editing software and others.

In other words, if you’re on an extremely tight budget, 4GB will do. If you’d like to have just enough, 8GB is the way to go. Finally, if you’re building a purpose built workstation or a server, you want as much memory as possible.


While at first glance it might appear that the memory choices can be difficult, they really aren’t. We’ve already covered most recommended brands, speeds and capacities. These 3 items will be all you need to pick the right memory for you. With this information you will be able to find best memory that will fit any budget.

We haven’t discussed server and laptop memory because they tend to follow the same rule as Desktop memory. You have to make sure you buy the correct standard and everything else applies. Speed, fitment, brand and others are shared across the board.

Server memory will usually provide additional features on top of desktop memory such as Error Correction (ECC), which can resolve memory problems while the system is running and not cause issues. If you’re building a server, then these extra features can come in handy however be aware that the price of memory goes up significantly as you add more features. Unless you’re specifically building a server, you will do fine with standard desktop memory.

Lastly, memory can be prone to frequent failures, but it’s one of the easiest components to test. We already have a memory testing guide which you can visit here: Testing Memory

It can help you isolate bad modules and find memory errors that cause instability and system crashes. Because memory is usually sold in kits, it’s typical that you might sometimes get a single defective stick. If you just got brand new memory and you’re experiencing system crashes, blue screen errors and others, then definitely check out our guide listed above to help you resolve that problem. Most manufacturers we’ve listed earlier in this guide have excellent customer service and replacement plans, and some even have upgraded shipping plans for certain memory modules.

We hope that this guide has been informative and that it has helped you understand how to choose system memory. Of course, additional details and suggestions are always recommended by our staff during your system purchase, and we do this every step of the way to guarantee you’re getting all the right components in your custom computer.