Difference between SDRAM and DDR (2023)

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SDRAMmiRDAThey are two different types of RAM. SDRAM was released in 1993 and the latest SDRAM variants are DDR1, DDR2 and DDR3. SDRAM stands for Synchronous Dynamic Random Access Memory. SDRAM was very common before the release of DDR. SDRAM is single data rate memory. On the other hand, DDR stands for Double Data Rate. As its name implies, DDR provides twice the data transmission in each clock cycle compared to SDRAM.

(Video) Different Types of DRAM: SDRAM/DDR1/DDR2/DDR3/DDR4/LPDDR/GDDR

Read this article to learn more about SDRAM and DDR and how they differ from each other.

What is SDRAM?

SDRAMit is a type of DRAM that can operate at a relatively higher speed compared to conventional DRAM. SDRAM was first released in 1993 by Samsung. SDRAM has a simple and low-cost design, but its manufacturing process is quite complex.

SDRAMs consume more power to function. Being a type of dynamic random access memory, they require frequent data updating. However, SDRAMs can operate more efficiently. Because it is synchronous memory, it is in sync with the CPU clock. Therefore, it can operate in a more complex way compared to normal DRAM.

(Video) RAM Explained - Random Access Memory

SDRAM also consists of an internal finite state machine that channels incoming instructions. This means that SDRAMs can accept a new incoming instruction before finishing processing the old one.

What is DDR?

RDAit is an extended version of SDRAM used in most modern computers as RAM. As its name implies, DDR SDRAM responds twice as fast because it uses the rising and falling edges of the clock signal. DDR does not indicate speed, but represents the number of times of data transmission per clock cycle. Therefore, DDR can transfer data twice per clock signal cycle.

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. DDR SDRAM has become very popular due to its low cost, double data rate, and low power consumption.


Difference Between SDRAM and DDR

The following table highlights the important differences between SDRAM and DDR:

DefinitionSDRAM stands for Synchronous DRAM (Dynamic Random Access Memory).DDR stands for Double Data Rate SDRAM.
pins and notchesSDRAM has 168 pins and 2 connector notches.DDR has 184 pins and 1 notch on the connector.
Release yearSDRAM was released in 1997.DDR was released in 2000.
Transfer speedSDRAM has a slow transfer speed.DDR is twice the speed of SDRAM.
voltage requirement3.3 volts.2.5 volts as standard. 1.8 V as low voltage.
clock speedThe clock speed varies between 100 MHz and 166 MHz.The clock speed varies between 133 MHz and 200 MHz.
working speedThe speeds used are 66 MHz, 100 MHz and 133 MHz.The speeds used are 200 MHz, 266 MHz, 333 MHz and 400 MHz
data speedThe SDRAM data rate is 0.81.3 GB/s.The DDR data rate is significantly higher at 2.13.2 GB/s.
prefetch time1 ns.2 ns.
hold strategySDRAM waits for the previous read/write operation to complete before continuing with another operation.DDR does not wait for the previous read/write operation to complete before continuing with another operation.


The most important point to note here is that SDRAM transfers a word of data once per clock while DDR transfers data twice per clock.


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