DDR
The simplest way to design an electronic circuit is to make it perform one transfer per clock
cycle (SDR technique uses this). This requires the clock signal to change twice per cycle. When
operating at high bandwidth, signal integrity limitations constrain the clock frequency. By using
both edges of the clock, the data signals operate with the same limiting frequency but doubling
the total transmitted data. It was an improved version of SDRAM which uses an SDR technique
for data transmission.
This technique was an improvement over its predecessor SDR (single data rate) and has been
succeeded by an improved version named QDR (quad data rate). A double data rate clock
cycle looks as follows:-
DDR-Characteristics of DDR:
• Transmits data twice per cycle (wave/clock), firstly at the the rising edge and
tehn at falling edges of a clock cycle
• Each clock cycle has a unidirectional flow of data
• DDR SDRAM technology consumes less power than older SDRAM modules,
which expanded 3.3 volts compared to DDR SDRAM’s 2.6 volts.
• DDR operates at same frequency as the clock cycle.
DDR-advantages and disadvantages
► Advantages of DDR:
• Higher levels of transmission speeds are obtained
• Reduces the number of cycles required to perform a task
• Reduces the component cost required
• Allows for smaller form factor computing devices
► Disadvantages of DDR:
• Slower compared to QDR (quad data rate) technique
• Devices accommodating DDR technique produces more heat
SDRAM DDR
It refers as synchronous dynamic random access memory It refers as Double data rate SDRAM
SDRAM has 168 pins and two notches at the connector DDR has 184 pins and a single notch at the connector.
SDRAM was released in 1997 DDR RAM was released in 2000
DDR can transfer data at roughly twice the speed of
SDRAM has less speed in comparison DDR
SDRAM.
it’s working on 3.3 volts it’s working on 2.5 Volts (standard); 1.8 V (low voltage)
SDRAM speed is considered as 66 MHz, 100 MHz, 133 DDR working on speed as 200 MHz, 266 MHz, 333 MHz,
MHz 400 MHz
SDRAM’s Internal rate range is (100 Mhz-166 Mhz) DDR’s Internal rate range is(133 Mhz – 200 Mhz)
Data rate of SDRAM is (0.8-1.3) GB/s Data rate of DDR is (2.1-3.2)
SDRAM prefetch timing is 1ns DDR prefetch timing is 2ns
SDRAM is waiting wait for the completion of the previous DDR is not waiting wait for the completion of the previous
command to be able to do another read/write operation. command to be able to do another read/write operation.
RDRAM
RDRAM
► Rambus Dynamic Random Access Memory is a full form of RDRAM. This type of RAM
chips works in parallel, which allows you to achieve a data rate of 800 MHz or 1,600
Mbps. It generates much more heat as they operate at such high speeds.
► Compared to other contemporary standards, Rambus showed increase in latency, heat
output, manufacturing complexity, and cost. Because of more complex interface
circuitry and increased number of memory banks, RDRAM die size was larger than that
of contemporary SDRAM chips, and results in a 10–20 percent price premium at 16 Mbit
densities (adding about a 5 percent penalty at 64 Mbit).[2] Note that the most
common RDRAM densities are 128 Mbit and 256 Mbit.
► PC-800 RDRAM operated with a latency of 45 ns, more than that of other SDRAM
varieties of the time. RDRAM memory chips also put out significantly more heat than
SDRAM chips, necessitating heatspreaders on all RIMM devices. RDRAM includes
additional circuitry (such as packet demultiplexers) on each chip, increasing
manufacturing complexity compared to SDRAM.
