Other external memory types

There are a variety of memory types that have been introduced over the years that are or have become more common with FPGAs. I want to briefly touch on them as you might be interested in them for your own projects in the future.

Quad Data Rate (QDR) SRAM

Quad Data Rate (QDR) SRAM is commonly used in networking applications. Like DDR memory, data is transferred on both edges of the clock for performance. Unlike DDR, QDR has both read and write channels, so you can issue read and write commands simultaneously. Also, unlike DDR DRAM, this is an SRAM, so there are no refresh cycles and the latency for a read or write can be as low as about 13 clock cycles at 300 MHz.

QDR has a much larger capability than FPGA internal memory, but much less than DDR. It's also relatively expensive, which is why it's mostly used in networking applications.

HyperRAM

HyperRAM is a type of self-refreshing DRAM designed for Low Pin Count (LPC) applications...