What is DDR Memory?
Computer memory can be a confusing subject with strings of numbers and arcane acronyms thrown around like there was no tomorrow. Luckily, it's actually relatively simple to understand once you take the time to think about it.
How Does DDR Differ from SDRAM?
DDR differs from its predecessor both physically and electrically. It came to be because faster processors needed faster memory and they were running out of ways to do that. The memory bus was already running over 100 MHz and wasn't fast enough, and dual channel memory was still on the horizon. Doubling the data rate was the most effective option available, and it led to all subsequent memory developments:
- Electrical Differences: DDR has an effective data rate of double the base memory bus, so DDR 333 runs at a base speed of 166 MHz with two ticks of data on every clock. It also runs at 2.5 volts as opposed to its predecessor's 3.3 Volts per module.
- Physical Differences: Both come in 133-millimeter DIMM format, but DDR uses a 184-pin package while SDRAM only has 168 pins. Laptop memory modules, or SO-DIMMs are different again, with 200 pins for DDR memory and 144 pins for SDRAM.
How Do You Install RAM?
On one level, installing a 1 GB PC2700 DDR-333MHz stick of Kingston RAM is very simple; you just click it into the slot and snap the two levers closed to lock it into place. On another level it's a little more complicated as there are a number of decisions you need to make before you open up the case and snap a new stick of RAM into place:
- Capacity: You need to know how much RAM your motherboard supports and what size modules. Some may support 4 GB of RAM with two 2 GB sticks, while others may need four 1 GB sticks.
- Channels: Dual channel desktop DDR SDRAM has to install in matched pairs. For 1 GB PC 2700 DDR, you need two 512 MB sticks, and two 1 GB sticks for a 2 GB kit. Both sticks need to be the same speed and latency, so it's a good idea to get both from one manufacturer such as Kingston.
- Data Protection: Servers use EEC and registered memory; most home users are fine with unbuffered DDR1, which is also faster as data protection adds latency.