Also known as “DDR2-533,” PC2-4200, and PC2-4300. A rating for the performance of SDRAM chips. The “4200” portion roughly represents the transfer rate in MBps (megabytes per second) – with PC4200 RAM, the chips are rated for approximately 4.2GBps (gigabyte per second) speeds. PC4200 chips are DDR2 chips, which send data on both the rising and falling edge of the clock, with a clock speed of 133MHz and a bus speed of 266MHz, resulting in 533 million transfers per second.
The PC rating for a PC4200 RAM chip can be approximated using either of two formulas:
transfers per second x 8 (bits per transfer)