To determine the maximum tested speed of a DDR SDRAM memory module, every DDR module has a label. On this label is a number PCxxxx, where xxxx gives the maximum supported bandwidth of the memory module.
To find the data rate of the memory module, divide this number by 8, and you get an approximation of the data rate of the memory module, or the "speed." For example, to find the data rate of PC3700 memory use the following equation: 3700 / 8 = 462.5. This is an approximation of the data rate and would commonly be labeled as 466MHz memory.
For simplification, some of the numbers get rounded up or down and may not exactly match a data rate listed. Memory does not actually have a speed, but this number is the maximum tested rate at which the memory transfers data. Use the table below for a list of the PC ratings and DDR data rates of commonly available memory modules.
Check the Online System User’s Guide or Owner’s Manual on Dell Support for the Dell system in question to determine what memory functions with your system.