My synapse is stuck

You have some memory marked PC2-6400. What memory clock speed would match this memory?

A) 100 MHz

B) 133 MHz

C) 166 MHz

D) 200 MHz

E) My memory could use some help

The answer: D) 200 MHz

Memory marked PC2 is DDR2 SDRAM. Memory marked PC would be DDR SDRAM, and PC3 is DDR3. For DDR2 memory, you calculate the data rate of 6,400 MB/s by calculating the memory clock rate x 2 (DDR 2 bus clock multiplier) x 2 (dual rate) x 64 (number of bits transferred) / 8 (bits per byte). If you solve for the memory clock rate, the answer is 200 MHz.

Although it’s useful to know what the formula represents, the shortcut is to remember the factors for the different memory types. For DDR memory, the factor is 16. For DDR2 the factor is 32, and for DDR3 the factor is 64.

Since this is DDR2 memory, you can quickly divide 6,400 by 32 and get the answer of 200.

Want to know more? Watch “Identifying Memory Types.”

Memory comes in many shapes and sizes. In this video, you’ll learn about RAM, ROM, static RAM, dynamic RAM, synchronous DRAM, and how to calculate the throughput rates of DDR memory.