Specifications

Computer Architecture and Maintenance (G-Scheme-2014)
OverView and Features of SDRAM , DDR, DDR2 and DDR3
Q.What is SDRAM
Ans. Synchronous dynamic random access memory (SDRAM) is dynamic random
access memory (DRAM) with an interface synchronous with the system bus carrying
data between the CPU and the memory controller hub. SDRAM has a rapidly
responding synchronous interface, which is in sync with the system bus. SDRAM waits
for the clock signal before it responds to control inputs.
SDRAM preceded double data rate (DDR). The newer interface of DRAM has a double
data transfer rate using both the falling and rising edges of the clock signal. This is
called dual-pumped, double pumped or double transition. There are three significant
characteristics differentiating SDRAM and DDR:
1. The main difference is the amount of data transmitted with each cycle, not the
speed.
2. SDRAM sends signals once per clock cycle. DDR transfers data twice per clock
cycle. (Both SDRAM and DDR use the same frequencies.)
3. SDRAM uses one edge of the clock. DDR uses both edges of the clock.
SDRAM has a 64-bit module with long 168-pin dual inline memory modules (DIMMs).
SDRAM access time is 6 to 12 nanoseconds (ns). SDRAM is the replacement for
dynamic random access memory (DRAM) and EDO RAM. DRAM is a type of random
access memory (RAM) having each bit of data in an isolated component within an
integrated circuit. Older EDO RAM performed at 66 MHz.
Detailed Explanation
With older clocked electronic circuits, the transfer rate was one per full cycle of
the clock signal. This cycle is called rise and fall. A clock signal changes two times per
transfer, but the data lines change no more than one time per transfer. This restriction
can cause integrity (data corruption and errors during transmission) when high
bandwidths are used. SDRAM transmits signals once per clock cycle. The newer DDR
transmits twice per clock cycle.
SDRAM is improved DRAM with a synchronous interface waiting for a clock
pulse before it responds to data input. SDRAM uses a feature called pipelining, which
accepts new data before finishing processing previous data. A delay in data processing
is called latency.
DRAM technology has been used since the 1970’s. In 1993, SDRAM was implemented
by Samsung with model KM48SL2000 synchronous DRAM. By 2000, DRAM was
replaced by SDRAM. In the beginning SDRAM was slower than burst EDO DRAM
Prepared By – Prof. Manoj.kavedia (9860174297 – 9324258878 ) (www.kavediasir.yolasite.com)
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