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Difference between SDRAM and DDR
SDRAM and DDR are two different types of RAM. SDRAM was released in 1993 and the latest variant of SDRAM are DDR1, DDR2 and DDR3. SDRAM stands for Synchronous Dynamic Random Access Memory. SDRAM was very common before the release of DDR. SDRAM is a single data rate memory. On the other hand, DDR stands for Double Data Rate. As the name indicates, DDR provides double data transmission in each clock cycle as compared to SDRAM.
Read through this article to find out more about SDRAM and DDR and how they are different from each other.
What is SDRAM?
SDRAM is a type of DRAM that can run at relatively higher speed as compared to a conventional DRAM. SDRAM was first released in 1993 by Samsung. SDRAM has a simple design and low cost, but their manufacturing process is quite complex.
SDRAMs consume more power to run. Being a type of dynamic random access memory, they require frequent data refreshing. However, SDRAMs can operate more efficiently. Since it is a synchronous memory, it is synchronized with the clock of the CPU. Thus, it can operate in a more complex fashion as compared to a normal DRAM.
SDRAMs also consist of an internal finite state machine that pipelines the incoming instructions. That means, the SDRAMs can accept a new incoming instruction before it has finished processing of the previous one.
What is DDR?
DDR is an extended version of SDRAM used in most modern computers as RAM. As the name indicates, DDR SDRAM responds at double rate because it uses both the rising and falling edges of the clock signal. DDR does not indicate the speed, but it represents the number of data transmission time per clock cycle. Thus, DDR can transfer data twice per cycle of the clock signal.
In computer systems, DDR is used for data transmission between the CPU and the north bridge. The clock speed of a typical DDR memory is at least 200 MHz. The DDR SDRAM became very popular due to its low cost, double data transfer rate, and low power consumption.
Difference between SDRAM and DDR
The following table highlights the important differences between SDRAM and DDR −
| Key | SDRAM | DDR |
|---|---|---|
| Definition | SDRAM stands for Synchronous DRAM (Dynamic Random Access Memory). | DDR stands for Double Data Rate SDRAM. |
| Pins and notches | SDRAM has 168 pins and 2 notches at connector. | DDR has 184 pins and 1 notch at connector. |
| Year of Release | SDRAM was released in 1997. | DDR was released in 2000. |
| Transfer speed | SDRAM has low transfer speed. | DDR has twice the speed of SDRAM. |
| Voltage Requirement | 3.3 Volts. | 2.5 Volts as standard. 1.8V as low voltage. |
| Clock Speed | Clock Speed ranges between 100 MHz to 166 MHz. | Clock Speed ranges between 133 MHz to 200 MHz. |
| Working Speed | Speeds used are 66 MHz, 100 MHz and 133 MHz. | Speeds used are 200 MHz, 266 MHz, 333 MHz and 400 MHz |
| Data Rate | The data rate of SDRAM is 0.81.3 GB/s. | The data rate of DDR is significantly higher at 2.13.2 GB/s. |
| Pre-fetch timing | 1 ns. | 2 ns. |
| Wait Strategy | SDRAM waits for completion of previous read/write operation to continue other operation. | DDR does not wait for completion of previous read/write operation to continue other operation. |
Conclusion
The most important point that you should note here is that SDRAM transfers a word of data once per clock cycle, whereas DDR transfers data twice per clock cycle.
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