Difference Between SDRAM and DDR

SDRAM and DDR are both two subtypes of Random Access Memory that have fallen into different categories and generations of the main type of RAM called DRAM.

They have inbuilt memory ICs (Integrated Circuits) that assist them in the smooth running and functioning as a RAM for the hardware device that it is connected to.

SDRAM vs DDR

The main difference between SDRAM and DDR is that the data transferring speed of both the RAMs vary with a small difference which is more than enough for the users to purchase the faster RAM provided it satisfies other properties fulfilled by the subtype. DDR is faster than SDRAM by twice the speed rate giving it greater functionality.

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SDRAM is one of the first generations of RAMs released as a prototype of the parent DRAM. Its synchronization with the clock signal is the main determining factor when users need RAM. It was in demand for the longest period until a new generation of RAMs was unfolded and the drop in the market for SDRAM users ultimately almost nullified its production.

DDR is the prototype to the second generation of the main DRAM that has a higher synchronization capacity with the signal clock that helps in the data transfer or completion of a specific operation assigned to the DDR. Owing to its structural difference from the other generation of RAMs, it has had a lower market value.

Comparison Table Between SDRAM and DDR

Parameters of ComparisonSDRAMDDR
Year of Release19972000
SpeedSlower in comparisonAlmost twice as fast as SDRAM
Voltage at Which it Works3.3 volts2.5 volts (standard DDR) and 1.8 volts (DDR with low voltage)
Data Rate0.8-1.3 Gigabytes per second2.1-3.2 Gigabytes per second
Data Transfer Time Between Every Cycle1 Nanosecond2 Nanosecond

What is SDRAM?

SDRAM stands for Synchronous Dynamic Random Access Memory released in the year 1997.

It has been manufactured with many features taken off the DRAM memory supplement in a way making it the first in line among many generations of DRAM to come.

SDRAM is commonly categorized as the first generation of the parental type DRAM, giving it credibility in the market as many newly launched products are kept off-limits by purchasers.

It has an interface that helps in the synchronizing process. This just shows that SDRAM can wait for clock signals to be given to it before each operation is completed.

Its physical structure comes with two notches that are to act as the point of connection and with about 168 pins to help in the data transfer and storage.

As it is a RAM, it functions as long as the connected main device or system remains active or logged in by the user.

Therefore, erasing all of its activity and temporarily storing data as soon as the device is shut down or logged out.

It has a comparatively less speed when seen together with the later generations of the parental DRAM.

With speeds ranging between 66MHz, 100MHz, and 133MHz, it could be called one of the slowest available RAM.

This lack of speed is because a single word is transmitted between synchronized operations per clock cycle.

This happens as SDRAM makes use of just the rising edge of the synchronized signal for transferring the data.

This means that SDRAM can’t overlap operations.

What is DDR?

DDR stands for Double Data Rate RAM that was released in 2000.

Due to its product type and eventual complete look, it has been called a second generation of the DRAM and a sister prototype of the SDRAM.

It holds multiple features of the basic SDRAM giving it a place in the synchronous dynamic RAM family.

It is also called DDR1, though this name has been later given to other newly constructed RAMs in the same generation.

Its structural construction includes a single notch point to which external device connections are made and it gives the DDR the connection capability.

To assist the data transfer and storage functions of the DDR, it has got around 184 pins.

Its data transfer capacity is almost twice that of the RAMs in the previous generations and also in comparison to the parent DRAM.

With transfer speeds ranging from 200 MHz to 400 MHz with minor values in between such as 266 MHz and 333MHz.

This speed difference is catered to with the help of the fact that DDR doesn’t have to wait for the completion of each operation or data transfer to move on to the next.

This means that DDR can overlap its operations and data transfer in a hassle-free manner doubling up the speed and can read two values per cycle.

The reading of 2 values is achieved by the reading of both the rising edge and falling edge of the assigned clock signal.

Main Differences Between SDRAM and DDR

  1. While SDRAM has a structural makeup of two connection notches that assist in hardware connection and about 168 external pins for transfer of data and operations, DDR has got a single notch at the connector and a greater number of the pin that is 184.
  2. DDR has a speed category ranging from 200 MHz, 266MHz, 333MHz, and 400MHz which is almost double the speed range given to SDRAM of 66MHz, 100MHz, and 133MHz.
  3. SDRAM is called the first generation of the parental DRAM whereas DDR is called the second generation of the prototype, both of which have their new variations combined with the features of the prototype.
  4. In the case of DDR, the microprocessor chip reads both the rising edge as well as the falling edge of the clock signal, but for SDRAM, only the rising edge is taken into consideration and thereby reducing the values read per cycle.
  5. The working voltage of SDRAM is at 3.3 volts whereas, in the case of DDR, the voltage value is different depending on the type of RAM. It ranges from 2.5 volts for the standard type and about 1.8 volts for the lower category depending on the purchaser’s needs.

Conclusion

Both SDRAM and DDR are variants of synchronous RAM that hold a lot of value on the movement of the signal clock to allow readings and the passing on of operations.

The memory chip that reads the clock cycles is a lot more complex than the operations itself, for it creates the pathway for the transfer of data on a pre-set pattern from the manufacturers.

In most common cases, the speed of RAM is shown in the Nanosecond units, but for the first and second generations of DRAM, the speed unit is MHz (MegaHertz).

The data reading chip in DDR can read two words or operational values per signal clock cycle.
SDRAM has to stop between operations and data transfer to allow the previously ongoing process to reach its completion.

References

  1. https://dl.acm.org/doi/abs/10.1145/1289816.1289877
  2. https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.371.397&rep=rep1&type=pdf#page=70
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