Memory Upgrade Resource Guide 2010 Introduction Corsair Labs works diligently to provide tools for our customers to assist them in making sound decisions when selecting components for building and upgrading their computers. Due to the progression of current memory offerings and current motherboard offerings, there are an increasing number of factors to consider before selecting memory for an upgrade. These factors can greatly impact the effectiveness of the upgrade. The most critical factors to consider when upgrading the memory in your computer are how many modules you will have in the system, whether or not you overclock your system, and which operating system you will be using. These factors are discussed in detail below. Figure 1 shows 4 Dominator GTs installed on an Intel P55 based motherboard. Figure 1
The Number of Memory Modules Used There are quite a few factors related to the number of memory modules used. Some are platform dependent and some apply to both AMD and Intel platforms. Understanding these factors is critical to selecting the correct memory for your upgrade. Memory Slot Loading Most new computers and motherboards have four or six DIMM sockets. Typically, when a new computer is purchased, OR when building a new PC, only half of these sockets are populated. So, upgrading the system is usually done by either [1] adding more DIMMs to the kit already in the system, or [2] putting in a new memory kit and discarding the old DIMMs. Figure 2 shows the Corsair CMD8GX3MA1600C8 kit with the included cooling fan. Figure 2 Page 2
For users opting to use four memory modules or six memory modules, referred to hereafter as 4-up or 6-up, there are many considerations. First, loading all the memory slots as opposed to loading half of the slots places a greater electrical load on the memory controller. This increased load can result in instability if the BIOS is not tuned or tweaked to compensate. The user should make certain that their motherboard BIOS allows adjustments to the memory controller voltage. Additionally, users should be certain that their cooling method is capable of cooling the CPU+ memory controller as it will generate more heat with all slots loaded and the increased voltage. Keep in mind that it is the number of modules that determines this electrical load and not the overall memory amount. For example, 6 modules place approximately twice the electrical load onto the memory controller as 3 modules regardless of module density. This is also true with 4 modules as opposed to 2 modules. Memory Controller Voltages The increased load of 4-up or 6-up is not an additional load on the memory modules. Many users mistakenly increase memory voltage when running all slots loaded and most often when trying to address stability issues. This is not necessary as a motherboard is configured to supply the BIOS set voltage to each DIMM slot, regardless of how many slots are filled. Increasing the memory voltage over the rated module voltage will not address a stability issue that is related to the memory controller voltage. Figure 3 shows Dominators 6-up on an X58 motherboard. Figure 3 Page 3
Fundamentally, the electrical limitations are the same for both Intel and AMD platforms. Adding memory modules places a greater load on the memory controller and may necessitate memory controller voltage changes. Also, performance and overclocking may be inhibited when running with all memory slots loaded. Mixing New Modules with Existing Modules A user that already has a pair of modules and adds a second pair should take care to purchase a kit as similar as possible to the original to have the greatest chance of successful integration. This ensures a high likelihood of success when running a system with all DIMM sockets populated. As seen in figure 4, it s common for users to upgrade both the memory frequency and density. However, this type of combination may be unstable and is not recommended. Figure 4 Memory changes dynamically and suitable memory for adding to an existing kit in the future may not be available as memory continues to evolve and improve. The best option Page 4
is to buy the amount of memory you desire in a single kit. Generally, it is not advised to combine memory made with different ICs or RAM chips, of different revisions or version numbers, different frequencies, or of different densities as compatibility issues may occur. Overclocking and Voltage Requirements These limitations are more prevalent when overclocking and are the primary reasons that the highest density kits are not available at the higher frequencies. Therefore, overall performance and overclocking goals must be balanced when users are deciding between density and frequency. Users wanting to utilize the all the memory slots on their system are not likely to be able to overclock as well as users using half the slots available nor will they be able to utilize the highest frequency memory to its full potential. Memory voltage requirements are also important and especially for Intel users. Current Intel Core i7, Core i5, and Core i3 users are advised by Intel to use memory rated for 1.65v or less. Most DDR3 memory produced in the past to operate above DDR1333 also required more than 1.65v to do so. DDR3 rated for more than 1.65v will not likely be able to run at its rated specifications at 1.65v. This means that older DDR3 kits are not suitable for Core i* processors for those users desiring maximum performance. Figure 5 shows the Corsair Dominator 1800C7 module which is rated at 2.0 volts. This voltage was a safe voltage for this module however, this module is not well suited for current Intel platforms. Not all current AMD DDR3 motherboards will supply 2.0v. Figure 5 Page 5
This voltage limitation does not apply to the AMD Phenom II processors at this time. Coincidentally, most current memory kits offered for AMD Phenom II systems are rated at 1.65v or less. However, this is due to the memory modules themselves and their voltage characteristics. Performance Profiles Both AMD users and Intel users now have the option of buying memory with memory performance profiles. These are pretested settings for the memory that can be utilized to automatically configure high performance memory settings in a quick and easy manner. AMD calls their method BEMP or Black Edition Memory Profiles. Intel s version is XMP, or Extreme Memory Profiles. In some instances due to motherboard, memory controller, or BIOS limitations these performance profiles may not work correctly when all memory slots are loaded. In these cases, users will need to configure their memory settings manually. Overclocking If you take a look at a current motherboard with overclocking options, you may see some specifications similar to this: Motherboard can support up to 6 memory modules,. up to 24 GB, DDR3 2000(O.C.)*/1866(O.C.)*/1800(O.C.)*/1600(O.C.)/1333/1066 Non-ECC, Un-buffered Memory Many users interpret these specifications too liberally and these specifications do not mean a board+cpu can run its maximum supported amount of memory and maximum memory frequency at the same time. It may do one or the other but typically not both simultaneously. A motherboard that can overclock to a given speed with 2 or 3 modules cannot overclock to that same given speed with 4-up or 6-up. Again, this is due to the increased electrical load memory controller and the increased heat that accompanies it. So, many users are disappointed when they add memory and their overclocking capability is reduced. They tend to fault the memory for this limitation when it is actually a physical limitation of the memory controller. A good analogy representing visualization of the above specifications is a passenger truck. Let s assume that the maximum hauling capacity of the truck is 12000 pounds representing 12GB of memory. The top speed of the truck is 200 mph representing a memory speed of DDR2000. These specifications do not mean that the truck can haul 12000 pounds at 200 mph. The physical limitations are similar for a memory controller as 12GB and 2000 are both tested maximums for this memory controller. When the memory controller speed is increased for overclocking, it simply cannot manage the same amount of memory at that overclocked speed for proper stable communication with the CPU. Page 6
Operating System With current motherboards, 32-bit operating systems are becoming more of an impediment. In most cases a 32-bit operating system will not be able to utilize more than 3.5GB of memory due to how the OS must handle Memory Mapped Input/Output, or MMIO, and assign memory addresses. In some instances, some chipsets and notebooks will be able to utilize more than 3.5GB total. However, most desktop boards and chipsets are going to have a minimum of a 512MB block of address space reserved for MMIO. This limits the address space to 3.5GB out of the installed 4GB available to the OS to assign to the system memory. In 2008 at the time we published the previous resource guide, a current motherboard typical at that time was going to reserve a 512MB block of address space for MMIO. In 2010, motherboards are typically reserving a 1024MB block of address space. So, users wanting their systems to see 4GB or more of system memory will need a 64-bit OS. Users that want to gain the full benefit of a memory upgrade will need to utilize a 64-bit OS so that the full amount of memory can be addressed. An user with a 32-bit OS can still benefit from an upgrade to 4GB in spite of the limit of the OS. How Does This Apply to My Laptop? The same basic rules apply for upgrading the memory in a laptop or netbook. More memory is going to help reduce the work load on the hard drive. Most laptops typically have a slower hard drive speed than the average desktop; 4200 or 5400rpm for laptops versus 7200 or faster for desktops. This is a power saving function that sacrifices performance for battery longevity. A new option that is yielding great results is the SSD, or solid state drive. SSDs offer vastly superior performance over rotational hard drives while using far less power. So in addition to upgrading the memory, an SSD is an excellent addition to a laptop or netbook. The primary Achilles heel for a laptop or netbook is the lack of system memory combined with slow hard drive performance. The lack of system memory leads to heavy page file usage. Heavy page file usage on a slow hard drive is a severe bottleneck to performance. So, if you have constant heavy page file usage on your laptop, this can cause a high level of input/output activity, called thrashing. Thrashing greatly reduces performance. Hard drive thrashing can cause stutter in video playback, game or application lag, slow page loads, and many other undesirable effects. A memory upgrade is one of the most effective laptop upgrades. Page 7
A memory upgrade combined with an SSD, using items like these shown in figure 6, can result in a phenomenal performance increase even with no upgrade in processor capability due to increased memory capacity, reduced page file usage or thrashing, and SSD performance. Figure 6 Most laptops have 1 or 2 memory slots due to size and space restrictions. The same rule of adding matched modules should be applied which means the user will have the original memory left over after the upgrade. Regardless, the performance benefits are worth it as much if not more than with a desktop. Corsair laptop memory is offered in 1GB (single SODIMM), 2GB (2 x 1GB SODIMMs) 4GB (2 x 2GB SODIMMs), and 8GB (2 x 4GB SODIMMs) kits. So, users should also keep the 64-bit OS option in mind when selecting the 4GB kits. However, even those users selecting 4GB with a 32-bit OS will benefit from the increased memory just like a desktop user. Page 8
The Decision Making Process A user contemplating a memory upgrade can follow a simple order in selecting a memory upgrade. The user should begin by prioritizing the upgrade focus on either increasing the density or increasing the memory frequency. Both can be done with the same kit but, there are limits to both as noted above. The process is simplified by focusing first on either density or frequency. Next, the user needs to decide if they intend to add memory to their existing memory or, if they intend to upgrade with an entirely new kit. The existing modules will have some bearing on the choice for the new modules with respect to both the type of modules and the number of modules. Figure 7 illustrates a few of the many options from which to choose. Figure 7 Of course, the user will need to keep budget in mind throughout the entire process also. Once these basic decisions are made the user can simplify it down to 2 essential options. Page 9
1. Select the density they want and then find the highest frequency modules available in that density that fall within their budget. 2. Select the frequency they want and then find the highest density modules available in that frequency and that fall within their budget. Of course there are many other factors to consider such as motherboard compatibility, esoteric concerns, and memory timings but those are beyond the scope of this paper. However, those concerns are more easily addressed after the criteria above have been established. A thorough understanding of the points addressed here will assist a user in making a much more informed and effective upgrade decision. Summary Our summary is essentially the same as the conclusions we reached in 2008 when we published our first guide. Users that are building new machines or users considering upgrading existing machines with more memory have many more things to consider before making a memory purchase than in the past. The choice of the operating system is essential and will apply at both stock and overclocked settings. In fact, a 64-bit OS may even eventually become a necessity. The number of modules has an impact on the performance of the memory controller that is independent of the operating system and must be accounted for. This will not change even as memory controllers continue to evolve. And, users that choose to overclock must make a careful assessment of both how much memory they want and how fast they want to attempt to run their memory. And, the motherboard selection is critical also and becomes more important as user expectations increase. Resource Listing We recommend the following resources for more useful information on this topic: RAM Guy Forums http://www.asktheramguy.com. The Corsair Memory Configurator http://www.corsairmemory.com/configurator/default.aspx Microsoft Knowledge Base article 929605 http://support.microsoft.com/kb/929605 Corsair SSD Information: Why SSD? http:///products/ssd_home.aspx Corsair AN902, 8GB or More of System RAM-Doing More with More Memory AN902: AN902: 8GB or More of System RAM Doing More With More Memory Page 10
Corsair AN811, Gaming Performance Analysis: 6GB vs 3GB AN811: Gaming Performance Analysis - 6GB vs 3GB Corsair AN806, Memory Upgrade Resource Guide http:///_appnotes/an806_memory_upgrade_resource_guide.pdf Corsair AN804,Gaming Performance Analysis: 4GB vs 2GB http:///4gb/. Corsair AMD Phenom II Memory Solutions http:///products/memory_home.aspx Corsair Intel Core i7 and Core i5 Memory Solutions http:///products/memory_home.aspx Corsair Notebook/Laptop/Netbook Memory Solutions http://www.corsairmemory.com/products/notebook_home.aspx AMD Phenom II Processor Information http://www.amd.com/us/products/desktop/processors/phenom-ii/pages/phenom-ii.aspx Intel Core i7 and Core i5 Information http://www.intel.com/products/desktop/processors/index.htm?iid=desk_nav+proc Page 11