Here’s a quick cheat sheet for DDR2:
- 266MHz FSB * 2 transfers = DDR2-533 * 8 bytes = PC2-4200
- 333MHz FSB * 2 transfers = DDR2-667 * 8 bytes = PC2-5300
- 400MHz FSB * 2 transfers = DDR2-800 * 8 bytes = PC2-6400
- 500MHz FSB * 2 transfers = DDR2-1000 * 8 bytes = PC2-8000
- 533MHz FSB * 2 transfers = DDR2-1066 * 8 bytes = PC2-8500
However, this cheat sheet with today’s technology isn’t entirely accurate. As the miracle of technology sauntered along, engineers in the computer industry realized that the operating speed of memory was fast eclipsing the achievable operating speed of the front side bus, so the wonder of “Dividers” was conceived. A divider is typically expressed as a ratio (Either #:# or #/#), and you are to literally divide these numbers to produce a decimal integer. The resulting number multiplies the frequency of the FSB you set in the BIOS and sets the RAM at that operating frequency.
Common dividers over the years:
- 1/2 = 0.50
- 2/3 = 0.67
- 3/4 = 0.75
- 4/5 = 0.80
- 5/6 = 0.83
- 6/7 = 0.85
- 7/6 = 1.16
- 6/5 = 1.20
- 5/4 = 1.25
- 4/3 = 1.33
- 3/2 = 1.50
- 2/1 = 2.00
Intel officially endorses two FSB frequencies: 266MHz (1066MT/s) and 333MHz (1333MT/s), and PC2-6400 is the standard memory for both of them as endorsed by Intel. Nevertheless, motherboard makers have certified their boards to run with much faster memory all thanks to dividers. Let’s have a look at a few:
Common DDR2 speeds for a Core 2 with a 266MHz FSB:
- 1/1: 266 FSB * 1.00 = 266MHz RAM = DDR2-533 = PC2-4300.
- 5/4: 266 FSB * 1.25 = 333MHz RAM = DDR2-667 = PC2-5400.
- 3/2: 266 FSB * 1.50 = 400MHz RAM = DDR2-800 = PC2-6400.
- 2/1: 266 FSB * 2.00 = 533MHz RAM = DDR2-1066 = PC2-8500.
Common DDR2 speeds for a Core 2 with a 333MHz FSB:
- 4/5: 333 FSB * 0.80 = 266MHz RAM = DDR2-533 = PC2-4300
- 1/1: 333 FSB * 1.00 = 333MHz RAM = DDR2-667 = PC2-5400
- 6/5: 333 FSB * 1.20 = 400MHz RAM = DDR2-800 = PC2-6400
- 3/2: 333 FSB * 1.50 = 500MHz RAM = DDR2-1000 = PC2-8000
On a quality motherboard, Core 2 Duos with a 266MHz FSB will allow you to use PC2-8500 where a Core 2 with a 333MHz FSB would not without overclocking. In the end, though, the Core 2s with that 333MHz FSB are the superior option, as the bandwidth disparity between what the FSB is pushing and what the RAM can handle is smaller on the 333MHz/PC2-8000 combination. This idea is what helped push the 333MHz-equipped chips into the market.
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