System memory: How Much? How Fast?
Skill Level: Beginner
DIMM – Dual Inline Memory Module – one physical unit of RAM that fits into one slot on the motherboard
SDRAM – Synchronous Dynamic Random Access Memory – The type of memory used in modern personal computers
DDR – Double Data Rate – Describes the ability to perform two actions for each clock cycle of the RAM
Memory, or RAM, is a crucial part of the PC gaming experience. Your computer’s operating system and every application you launch takes up space in system memory. Some programs, like those that monitor system health (CPU-Z or Core Temp) use negligible amounts, while modern games use substantial memory resources.
Since the vast majority of PC gamers still use Windows, we’ll go briefly into the amount of memory required just to boot your computer to desktop. According to Microsoft, Windows 7 requires 1GB for the 32-bit version and 2GB for 64-bit, minimum. I’m here to tell you that won’t get the job done on even a low-end gaming system. If for no other reason than additional memory recognition, it’s smart to use the 64-bit OS version whenever possible.
Without turning this article into a technical manual, I will explain that 32-bit Windows will only (theoretically) recognize a maximum of 4GB of RAM. This is due to the fact that every bit (literally) of information loaded into system memory is assigned to a memory address. Think of your RAM modules as little storage spaces full of rows and columns; a good analogy would be a blank spreadsheet, where the rows and columns converge to make cells. In this analogy, each cell corresponds to a memory address. As a result, a 32-bit system will only recognize 232, or a theoretical maximum of 4GB of memory. In contrast, a 64-bit system has the ability to recognize 264,or 16 exabytes (16 billion GB) of memory. Currently, computer motherboards define the upper limit of RAM that can be installed, as the best consumer units out there recognize “only” 64GB of RAM, or .0000004% of the amount of memory that can be recognized by a 64-bit OS. Suffice it to say that you will run out of slots long before your 64-bit OS runs out of memory addresses.
Practically speaking, the amount of usable memory is less because the system devotes some of the RAM to graphics (even if you are using a discrete GPU) and some elements of hardware control (for example ACPI), so that now, as I write this, the POS only recognizes 3.5GB of RAM installed.
Now that we’ve gotten that out of the way, let’s take a quick peek at the two most important factors that influence the performance of system memory, RAM clock speed and latency.
Clock speed works much the same as it does in a CPU, measuring the number of actions per clock cycle per second that your RAM is capable of delivering. However, since all modern RAM is DDR (Double Data Rate), it’s capable of performing an action twice during each cycle. If you imagine a wave form, the RAM can perform a function function both on the rising and falling side of each “wave”.
There are several kinds of RAM latency, which are addressed in a good article here, but for our purpose, gaming, I’m just going to say that less is better. Latency, as it applies to RAM, is the number of clock cycles required to perform a specific task. Latency increases with each version of DDR. For instance, DDR3 has less latency than DDR5. One of the facets of latency, tCAS or Time per Column Access Strobe is most usually represented as indicative of a module’s latency. Within DDR3, the current system memory standard, tCAS generally varies from 8 to 11 clock cycles. In this case, lower is better so very fast DDR3 will have a latency of 8, whereas “slower” memory will take 10 or 11 cycles to access a column.
In reality, even the slowest modules will fetch info faster than you can blink, so don’t get too hung up on latency. Many of the DDR3 modules out there are currently tCAS 9 or 10, and this is absolutely adequate for gaming. Like most high-end PC components, you need to find the sweet spot between price and performance. For instance, on Newegg right now you can get 8GB of DDR3 1600, tCAS 9 for $60. Stepping up to tCAS 8 for the same quantity and type of RAM will cost you $85 to $140. Only you can decide if the extra expense is worth the petite performance gain.
Now, let’s talk about system limitations on RAM. Your motherboard will only support a certain amount, no matter how much capacity the modules have. Low-end boards typically support 16GB, mid-range boards will handle 32GB, and top-of-the-line units will support 64GB. Also, check your board specifications carefully so you know what RAM speeds are supported. Some low-end boards only support up to 1600MHz DDR3, while higher-end boards, or those designed to support the more demanding AMD APU family will support higher speeds.
So, aside from the 32-bit OS limitation, your motherboard will be the arbiter of how much memory you can install. Not only are you limited by RAM support, but the number of slots present figures into how you will plan and execute memory upgrades.
Additionally, because Microsoft monopolizes the OS industry, they have chosen to place software limits on system memory recognition as detailed here. You’ll note the Windows 7 Home Basic limits memory to 8GB on 64-bit systems, and Home Premium limits RAM to 16GB. Higher-priced versions of Windows limit RAM to 192GB, more than any consumer board will recognize (to my knowledge).
Single vs. Dual Channel RAM
PC motherboards typically support single or dual channel memory configurations, although there are a handful of boards that support triple channel memory. Basically, when you open your case you will know what kind of configuration you have. If you have an odd number of DIMMs, you are running in single channel mode. If you have an even number, you’re running in dual channel mode.
In the past, dual channel configurations held a substantial advantage over single channel RAM. Now this is different- single channel setups are only about 3-5% slower than dual-channel, so if you are unsure about how much memory you will need and especially if you are using a low-end or small form factor board with only two slots, it’s perfectly OK to go with a single stick until you can evaluate the system’s real-world performance.
There are some do’s and don’t with RAM upgrades.
First, unless you own one of the very few boards out there that supports DDR2 and DDR3, don’t try to mix different module types. The stick will not fit and you will end up destroying your board, the RAM or both if you try to make it fit. General rule of thumb with PCs- if it takes any kind of serious physical force to make something happen, you’re not doing it right. Step back and regroup.
Your system will only run as fast as the slowest, most latent module allows. So, if you are planning to add to an existing quantity of RAM, take the time to remove one of the existing modules (detailed below) and examine the label to determine clock speed and latency, then use these as your guidelines when buying new RAM. If you are replacing your system RAM, observe your motherboard’s limits.
It is not necessary to add the same “size” module. For instance if you are working with a Dell or HP that has only one module installed (common on lower-end factory systems). Let’s say you have a tower that has 4GB RAM in the form of a single stick. There are only two total DIMM slots available and one is utilized before the upgrade. Provided you use the same type and speed of module, you can install 1-16GB in the second slot within the limits of the board’s memory support. It’s a good idea to examine the board’s architecture to see how dual-channel support works on that specific board. In most cases, motherboards have a primary slot or slots, depending on the total number available. Usually, if you are using two different size DIMMs, you want to seat the larger module in the first slot. Doing so will ensure all memory is recognized in dual-channel mode. Seating the smaller module in the primary slot may cause the board to recognize only a portion of the larger module as dual-channel.
For instance, say you have a basic system with 2GB RAM. You want to use the existing DIMM and add 4GB for a total of 6GB. The existing memory should be installed in the primary slot from the factory, but may not be (with only one stick you’re using single-channel configuration). If you put the larger DIMM in the second slot, the board may only recognize part of it as dual-channel. In this example, placing the larger module in the second slot may result in the recognition of the existing module (2GB) and half of the second module (2GB) as dual-channel, with the remainder of the new stick operating in single-channel mode.
Even though Microsoft lists 1GB and 2GB (32 and 64-bit, respectively) as minimums, I would say for gaming the following applies. If you are stuck with a 32-bit OS, go ahead and install 4GB of RAM. While it’s true that you won’t be utilizing all of the installed memory, 2GB sticks are pretty cheap these days and I look at it this way. I’m getting half a million extra addresses out of the system that I wouldn’t have with 3GB total RAM. And, if you ever upgrade your OS to 64-bit, you can use all of the module’s capacity.
For 64-bit Windows, I wouldn’t go with less than 4GB for a very basic gaming rig, and 8GB is preferred. You’re going to be using a video card (hopefully) which will use a chunk of system RAM. And some of the modern FPS titles can make use of up to 5GB RAM, so 8GB is really the least you want installed in your rig for the best performance. For this application, 1333MHz DDR3 is adequate but get 1600 if you can afford it for a few bucks more.
If you are using a high-end GPU, you’ll need more RAM. For the better NVidia or Radeon cards, or Crossfire or SLI configurations I would recommend 16GB minimum.
If you have an AMD APU, realize these chips run better the more memory you make available. Because the GPU is on the chip, it HAS to use system memory to function, it doesn’t have a separate quantity like discrete GPUs. So, using the above 8GB minimum, if you subtract 2-3GB for graphics use and the 2GB minimum that Windows requires, you’re left with very little to handle the meat and potatoes of the game application. If you go with an APU, plan to spend the money you saved on a video card for extra RAM. When I build APU systems, I use 8GB for a mainstream system and 16GB for a gaming tower, minimum. And, APUs like fast memory- for an APU build you’ll want 1600MHz minimum, and 1866 or 2133 if possible. If you have 16GB of good memory available to an APU, amount of RAM that’s available for gaming becomes much more palatable. 16GB minus 2GB (minimum) for Windows, minus 4-6GB for graphics still leaves you with about half your total memory to load and play games. Much better, and your graphics performance will benefit as well.
So, to sum up, 32-bit OS limits you to 4GB RAM. If you have a 64-bit system, check your motherboard’s maximum RAM and RAM speed support to determine how much memory you can add to your system. And strongly consider 8GB as minimum for better gaming performance for CPU/single-GPU configurations, and 16GB for APUs.
What you will need:
Phillips screwdriver (maybe, just to open the case)
As PC components go, RAM is among the sturdiest and least troublesome. Unless you get a bum stick out of the box, your RAM will usually last the life of the system.
Before you start, have your motherboard manual handy. If you don’t have the actual manual, go online and download it, then print the page that gives you a diagram of your motherboard. If you don’t have a printer, just make yourself a simple diagram of the number and designation of RAM slots. If your board has only two this is optional. If four slots are present, make sure you know which slots go together, i.e. whether each channel is side-by-side or staggered. Some boards will have two different colored slots to denote the channels, on others they are all the same color so check this out first. In all cases of which I’m aware, the slot closest to the CPU is the first slot.
To remove a RAM module, locate the bank of DIMM (Dual Inline Memory Modules) in the upper-right quadrant of your motherboard. They are easily recognizable as they are the only slots on the board that have little locking mechanisms on each side of the slot.
After grounding yourself, press down on both locking latches. The RAM module will pop up out of the slot. Sit it on a non-conductive surface while you work. If you are upgrading, write down the details of the DIMM while you have it out of the case.
If you are not removing any sticks, simply press down on the latches of the correct open slot to make sure it’s ready to receive the DIMM. Align the slot on the DIMM to the motherboard slot (offest from center so it will only go in one way) and press down firmly until the latches swivel up and click into place on the DIMM. That’s it, memory installed.
After you install the new DIMM(s), power up your computer and enter BIOS. The computer should recognize the additional RAM and correctly list the size and speed of the modules you added.
To my knowledge, RAM is RAM provided you are using the correct type- DDR2 or DDR3. However, there is one exception. Some newer DDR3 modules optimized for FM2/+ (AMD) and Haswell (LGA 1150, Intel) CPUs will not work in older (especially Sandy Bridge) boards. The modules will fit fine and install correctly, but the system will not recognize they are there. No matter what you do, the memory is invisible and therefore useless to the system, so if you do own a Sandy Bridge system, or you’re using RAM from an older AMD platform be very careful when purchasing RAM and avoid any that says it is “optimized” for FM2 or Haswell.
Aside from that, you shouldn’t have any problem with RAM installations. However, there’s always the chance that a new module is defective from the factory.
If you don’t fall into the Sandy Bridge category but your system does not recognize the new RAM, shut down the system, open the case and re-seat ALL of the memory modules. Reboot and hopefully your system will now recognize the new DIMMs.
If the RAM is still not recognized, power down and remove the DIMMs. Place the new DIMM in a slot you know is working (the one from which you removed the existing system memory). Attempt to reboot. If the system will not boot, the new DIMM is defective and should be returned. If the system does boot, you may have a bad slot on the board. Shut down the system again and seat a module known to function correctly (the original DIMM) in the slot you tried to install the new memory. Boot the system. If the original, working DIMM is not recognized the slot itself is bad. If your board has four slots, you can move the two DIMMs to the other set of slots. If your board has only two slots, you’re kind of stuck. In either event, a failure in the DIMM slot can indicate the board is on its way out and you should consider replacing it.
That’s it. Like the RAM modules themselves, troubleshooting is pretty simple.
If you have any questions or comments please feel free to leave them, I’ll respond ASAP. Thanks for reading.
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