Synchronous-DRAM

Synchronous DRAM coordinates its command interface with a clock. A controller issues commands at defined clock boundaries rather than treating every access as an independently timed asynchronous cycle. The storage cells remain dynamic and require refresh. Synchronous describes the interface timing, not a change from capacitive storage to static latches.

A read involves more than presenting an address. The controller activates a row, waits for the required internal operation, and issues a read selecting a column. Data arrives after the configured read latency. Bank state and timing constraints determine when the next operation is legal, so a clock does not make memory access instantaneous.

Synchronous DRAM Conceptual comparison; not a manufacturing specification or scale drawing Command sequence ACTIVATE row Wait → READ column Data phase Configured CAS latency Programmed burst Maintenance PRECHARGE when required Periodic refresh Schematic sequence only; the datasheet specifies the timing intervals and legal command combinations.

Burst transfers make the interface useful for sequential data. After a starting address, the memory can supply a programmed sequence of words. The controller need not repeat the entire row-opening operation for each word in that burst. ISSI’s IS42S16400 is a concrete example of a banked synchronous DRAM with programmable operating modes.

Banks and refresh shape the available bandwidth. The controller may schedule work across banks, but it must still respect activation, precharge, and refresh requirements. Peak pin bandwidth describes a favorable sustained transfer condition. Random-access workloads, row conflicts, and refresh reduce the bandwidth that an application actually sees.

SDRAM is the abbreviation, while SDR identifies single-data-rate operation. In 1990s terminology, SDRAM often means the original single-data-rate family. DDR SDRAM is also synchronous DRAM, but transfers data at twice the edge rate. State the generation explicitly when discussing modules, controllers, and compatibility rather than treating the abbreviation as a complete specification.

Sources and further reading. [ISSI IS42S16400 SDRAM datasheet](https://www.issi.com/WW/pdf/42S16400.pdf); [Rambus double-data-rate explanation](https://www.rambus.com/double-bus-rate-technology/).

Read Synchronous DRAM as a clock-coordinated dynamic memory whose throughput depends on command scheduling, bursts, and bank timing.

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