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Memory speeds and compatability

Adding more memory to your PC is one of the best and easiest ways to improve system performance. But before clicking that “buy” button on this or any website, it’s important to make sure the memory you are buying is compatible with your PC.

DDR4 memory is the latest generation of memory for computing applications and offers many benefits over previous generations of memory including lower latencies, higher speeds, and more. One thing to keep in mind is that memory needs to be the same type - memory modules are not forward or backward compatible in terms of generation types so DDR3 will not work in DDR2 or DDR4.

Memory is designed to be backward compatible within its generation, so generally speaking, you can safely add faster memory to a computer that was designed to run slower memory. However, your system will operate at the speed of the slowest memory module installed.

We recommend that you use either the Crucial Memory Advisor™ or Crucial System Scanner to find the right memory for your computer. Rather than give memory modules catchy names, the industry refers to modules by their specifications. But if you don't know a lot about memory, the numbers can be confusing. Here's a short summary of the most popular types of memory and what the numbers refer to.

 

Generations of memory explained

For double-data-rate memory, the higher the number, the faster the memory and higher bandwidth. Occasionally DDR memory is referred to by a "friendly name" like "DDR3-1066" or "DDR4-4000." When written this way, the number after "DDR" represents the generation. The number after the generation refers to the component's data transfer rate per second (/s). When referenced by the industry name, the numbers that follow "PC" and the generation refer to the total bandwidth of the module.
 
DDR4 Specs
 
Friendly name Industry name Peak Transfer Rate Data transfers/second (in millions)
DDR4-2400 PC4-19200 19200 MB/s 2400
DDR4-2666 PC4-21300 21300 MB/s 2666
DDR4-2933 PC4-23400 23400 MB/s 2933
DDR4-3000 PC4-24000 24000 MB/s 3000
DDR4-3200 PC4-25600 25600 MB/s 3200
DDR4-3600 PC4-28800 28800 MB/s 3600
DDR4-4000 PC4-32000 32000 MB/s 4000
 
DDR4 speeds start at 2400 MT/s and offer faster speeds and responsiveness than all other generations of memory. Optimized for gamers, professional designers, and enthusiasts who need to maximize data rates, DDR4 is for those who want the most from their system. Gaming modules typically have faster speeds, lower latencies, and unique design and heat spreaders. 
 
DDR3 Specs
 
Friendly name Industry name Peak Transfer Rate Data transfers/second (in millions)
DDR3-800 PC3-6400 6400 MB/s 800
DDR3-1066 PC3-8500 8533 MB/s 1066
DDR3-1333 PC3-10600 10667 MB/s 1333
DDR3-1600 PC3-12800 12800 MB/s 1600
 
Since 2007, DDR3 has been offering higher performance while requiring less power than DDR2 and DDR generations.   
 
DDR2 Specs
 
Friendly name Industry name Peak Transfer Rate Data transfers/second (in millions)
DDR2-400 PC2-3200 3200 MB/s 400
DDR2-533 PC2-4200 4266 MB/s 533
DDR2-667 PC2-5300 5333 MB/s 667
DDR2-800 PC2-6400 6400 MB/s 800
DDR2-1000 PC2-8000 8000 MB/s 1000
 

DDR2 PC2-4200 (commonly referred to as DDR2-533) memory is DDR2 designed for use in systems with a 266MHz front-side bus (providing a 533MT/s data transfer rate). The "4200" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 4200MB/s, or 4.2GB/s.

DDR2 PC2-5300 (commonly referred to as DDR2-667) memory is DDR2 designed for use in systems with a 333MHz front-side bus (providing a 667MT/s data transfer rate). The "5300" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 5300MB/s, or 5.3GB/s. PC2-5300 is backward-compatible for PC2-4200.

DDR2 PC2-6400 (commonly referred to as DDR2-800) memory is DDR2 designed for use in systems with a 400MHz front-side bus (providing an 800MT/s data transfer rate). The "6400" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 6400MB/s, or 6.4GB/s. PC2-6400 is backward-compatible for PC2-4200 and PC2-5300.

DDR2 PC2-8000 (commonly referred to as DDR2-1000) memory is DDR2 providing a 1,000MT/s data transfer rate). The "8000" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 8000MB/s, or 8GB/s. PC2-8000 is backward-compatible for PC2-4200, PC2-5300, and PC2-6400.

 
DDR Specs
 
Friendly name Industry name Peak Transfer Rate Data transfers/second (in millions)
DDR-200 PC-1600 1600 MB/s 200
DDR-266 PC-2100 2100 MB/s 266
DDR-300 PC-2400 2400 MB/s 300
DDR-333 PC-2700 2700 MB/s 333
DDR-400 PC-3200 3200 MB/s 400
 

PC1600 memory — which Crucial no longer carries — is DDR designed for use in systems with a 100MHz front-side bus, (providing 200 mega transfers per second [MT/s] data transfer rate). The "1600" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 1600MB/s, or 1.6GB/s. PC1600 has been replaced by PC2700, which is backward-compatible.

PC2100 memory — which Crucial no longer carries — is DDR designed for use in systems with a 133MHz front-side bus (providing a 266 MT/s data transfer rate). The "2100" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 2100MB/s, or 2.1GB/s. PC2100 is used primarily in AMD® Athlon® systems, Pentium® III systems, and Pentium IV systems. PC2100 has been replaced by PC2700, which is backward-compatible.

PC2700 memory — the slowest DDR memory speed that Crucial now carries — is DDR designed for use in systems with a 166MHz front-side bus (providing a 333 MT/s data transfer rate). The "2700" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 2700MB/s, or 2.7GB/s. PC2700 is backward-compatible for PC1600 and PC2100.

PC3200 (commonly referred to as DDR400) memory is DDR designed for use in systems with a 200MHz front-side bus (providing a 400 MT/s data transfer rate). The "3200" refers to the module's bandwidth (the maximum amount of data it can transfer each second), which is 3200MB/s, or 3.2GB/s. PC3200 is backward-compatible for PC1600, PC2100, and PC2700.

In SDRAM modules, the numbers that come after the "PC" refer to the speed of the system's front-side bus.

PC100 memory — which Crucial no longer carries — is SDRAM designed for use in systems with a 100MHz front-side bus. It is used in many Pentium II, Pentium III, AMD K6-III, AMD Athlon, AMD Duron, and Power Mac G4 systems. PC100 has been replaced by PC133, which is backward-compatible.

125MHz memory is SDRAM designed for use in systems with a 125MHz front-side bus. 125MHz has been replaced by PC133, which is backward-compatible.

PC133 memory is SDRAM designed for use in systems with a 133MHz front-side bus. It is used in many Pentium III B, AMD Athlon, and Power Mac G4 systems. PC133 is backward-compatible for PC100 and 125MHz.

PC66 memory is SDRAM designed for use in systems with a 66MHz front-side bus. It is used in the Pentium 133MHz systems and Power Macintosh G3 systems. FPM and EDO speeds are written in nanoseconds (ns), which indicates their access time; the lower the number, the faster the memory (it takes fewer nanoseconds to process data).

 

About adding faster memory ...

It may seem confusing, but faster memory will not necessarily make your system faster. You can't speed up your computer by adding faster memory if any of the other components in your computer (your processor or other memory modules) operate at a slower speed.

 

Keep in mind, that the right memory for your computer is the kind of memory it was designed to take. Check your system manual or look up your system in the Crucial Advisor tool™ or System Scanner to find the memory guaranteed to be 100 percent compatible or your money back!

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