Pretty sure this was covered somewhere in the A+ guides but I couldn’t remember what it was without dicking around with the numbers. Makes it hard to confirm you’re buying the correct RAM speed for your motherboard when the packaging lists one number and your motherboard specs list the other.
RAM speed is usually prefixed with “DDR” and suffixed with “MHz.” To find the PC___ value (e.g. PC8500) given the RAM’s speed, divide by 8.
PC8500 / 8 = 1062.5, which equates to 1066 MHz.
PC10600 / 8 = 1325, which equates to 1333 MHz.
To find the PC___ value based on the speed, multiply by 8.
DDR3 1066 x 8 = 8528, so PC 8500.
DDR3 1600 x 8 = 12800, so PC12800.
As you can see there may be some degree of rounding involved but the results should be obvious enough if you already know what speed multiples are out there (i.e. you’re looking at it on the shelf). If you know your motherboard only supports 1333 MHz, then 1333 x 8 gives you 10664, so PC12800 won’t work for you.