Sdr ram means what


Clock signal

SDRAM memory chips utilize only the rising edge of the signal to transfer data, while DDR RAM transfers data on both the rising and falling edges of the clock signal.

In a computer system, the clock signal is an oscillating frequency used to coordinate interaction between digital circuits. Simply put, it synchronizes communication. Digital circuits designed to operate on the clock signal may respond at the rising or falling edge of the signal.


The main difference between SDRAM and DDR memory is the doubled speed: DDR can transfer data at roughly twice the speed of SDRAM. PC133 SDRAM runs at 133 MHz, while 133 MHz DDR effectively runs at 133 MHz x 2 = 266 Mhz.

Physical difference

SDRAM has 168 pins and two notches at the connector while DDR has 184 pins and a single notch at the connector.

A comparison of different generations of DDR SDRAM chips.


Typical DDR SDRAM clock rates are 133, 166 and 200 MHz (7.5, 6, and 5 ns / cycle), generally described as DDR-266, DDR-333 and DDR-400 (3.75, 3, and 2.5 ns per beat). Corresponding 184-pin DIMMS are known as PC-2100, PC-2700 and PC-3200. The numbers represent the theoretical maximum bandwidth of the DDR SDRAM in megabytes per second (MB / s). For example, PC2100 has a theoretical maximum bandwidth of 2100 MB / s.


SDRAM was released first in 1997; DDR RAM was released in 2000. Subsequently DDR2, DDR3 and DDR4 SDRAM standards were released by JEDEC. DDR5 is in development.

Clock speed

You need to check the motherboard manual to see what RAM type (whether it is SDRAM or DDR RAM) is compatible with your system before purchasing memory. The clock speed for the memory chip should be synchronous with the computer's system bus. Both SDR and DDR RAM are offered at various clock speeds; installing a version faster than a motherboard can support is a waste of money.

Video explaining the difference


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"DDR vs SDRAM." Diffen LLC, n.d. Web. 9 May 2021. <>