Streaming video, cloud services, and mobile data are fueling the continuous expansion of global network traffic. To meet this demand, network systems must deliver higher line rates and the capability to process millions of packets per second. In such systems, packet arrival is inherently random, and each packet requires multiple memory operations for processing. This results in a need for hundreds of millions of memory accesses per second to perform lookups or maintain statistics in the forwarding table.
The packet processing rate is directly proportional to the random access rate. Modern network devices require both high random access performance (RTR) and high bandwidth to keep up with the rapidly growing traffic. RTR refers to the number of fully random memory accesses—either reads or writes—that a memory can perform per second. This metric is independent of the amount of data processed during each access and is measured in millions of transactions per second (MT/s).
Current high-performance DRAMs fall short of meeting the random access demands of advanced network systems. QDR-IV SRAM was specifically designed to deliver industry-leading RTR performance, making it ideal for applications that require intensive operations like updating statistics, tracking data flows, scheduling packets, or performing table lookups. As shown in Figure 1, QDR-IV outperforms other memory types by nearly double in RTR performance, even when compared to the highest-performing alternatives.
In the first part of this series, we will take a closer look at two variants of QDR-IV memory—XP and HP—and explore their clock speeds, read/write operations, and grouping capabilities.
**Different Types of QDR-IV: XP and HP**
There are two main variants of QDR-IV: HP and XP. The HP version operates at lower frequencies and does not support grouping operations, while the XP version is optimized for high-performance applications. It uses a grouping scheme and can operate at higher frequencies, allowing for greater throughput.
The read and write latency of QDR-IV depends on its operating frequency. Table 1 outlines the different operating modes and the corresponding frequencies supported by each mode.
**QDR-IV SRAM Architecture**
The QDR-IV SRAM features two independent ports—Port A and Port B. Because these ports can be accessed independently, any combination of read or write operations can achieve the maximum possible random data transfer rate. Each port utilizes a double data rate (DDR) address bus. For Port A, the address is latched on the rising edge of the input clock (CK), while for Port B, it is latched on the falling edge of CK or the rising edge of CK#.
Control signals (LDA#, LDB#, RWA#, and RWB#) operate at a single data rate (SDR) and determine whether a read or write operation is executed. Both data ports (DQA and DQB) feature DDR interfaces, enabling high-speed data transfers. The device uses a 2-word burst architecture and offers data bus widths of ×18 or ×36, providing flexibility for various system requirements.
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