PC2 5300 speed is 667MHz. PC2 6400 speed is 800MHz. If your system is designed for PC2-6400, it may or may not run on PC2-5300. It’s a bit slower when it’s running.
The “6400” refers to the module’s bandwidth (the maximum amount of data it can transfer per second), which is 6400 MB/s or 6.4 GB/s. PC2-6400 is backward compatible with PC2-4200 and PC2-5300.
PC2- indicates that the module uses DDR2 memory; PC- indicates that the module uses DDR memory. Other common speeds for DDR2 SDRAM modules are PC2-3200 (DDR2-400; 3200 Mbit/s throughput); PC2-5300 (DDR2-667); PC2-6400 (DDR2-800); and PC2-8500 (DDR2-1066).
Any memory that says either DDR2 or PC2 means the same thing. Likewise, DDR3 is the same as PC3. The other numbers indicate the speed of the memory.
Corsair seems determined to hold the record for the highest memory speed in production memory.
Yes, you can use 1333MHz and 1600MHz RAM together, especially if your PC supports more than 8GB RAM. If your PC still supports 8GB or less, there is still no problem as your PC will go back to using the smaller of the two MHz sizes for the 1333MHz and 1600MHz RAM sizes installed.
Basically all DDR2 DIMMs will fit. However, whether these DIMMs are electrically compatible (with the motherboard) is another matter. Check with memory manufacturers and check motherboard memory QVL for compatible memory.
Check both capacity and speed when choosing memory. Know the difference between form factors such as DIMM and SO-DIMM. Get at least 16GB of RAM to play modern games, and more if you’re multitasking.
PC2 is by far the more serious game – if you are looking for a simulation game where you can race, similar to real races, then this is the right choice. If you’re more of a casual gamer then PC3 is more fun to play around for an hour or so.
DDR2 PC2-6400 (commonly referred to as DDR2-800) memory is DDR2 designed for use in systems with a 400MHz front-side bus (and a data transfer rate of 800 MT/s offers).
PC2-4200 (DDR2-533) refers to the bandwidth of the memory. A PC2-4200 module has a bandwidth of 4.2 GB/s; hence it is referred to as PC2-4200. DDR2-533 refers to your system’s effective front-side bus speed.