# SDR SDRAM

> first generation of synchronous dynamic random-access memory

**Wikidata**: [Q6116127](https://www.wikidata.org/wiki/Q6116127)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/SDR_SDRAM)  
**Source**: https://4ort.xyz/entity/sdr-sdram

## Summary
SDR SDRAM (Single Data Rate Synchronous Dynamic Random-Access Memory) is the first generation of synchronous dynamic RAM, a type of computer memory that synchronizes operations with a system clock for improved performance. It introduced speed ratings such as PC66, PC100, and PC133, reflecting its maximum data transfer rates. As the foundational technology for modern SDRAM, it replaced older EDO RAM and was later succeeded by DDR SDRAM.

## Key Facts
- **Parent Class**: Synchronous dynamic random-access memory (SDRAM family).
- **Speed Ratings**: PC66, PC100, PC133 (indicating maximum data transfer rates).
- **Voltage**: Operated at 3.3 volts.
- **Standards Body**: Standardized by JEDEC.
- **Preceded By**: Extended Data Output Random Access Memory (EDO RAM).
- **Succeeded By**: DDR SDRAM (Double Data Rate SDRAM).
- **Form Factor**: Commonly used in DIMM (Dual In-line Memory Module) packages.
- **Technical Classification**: Technical standard and subclass of synchronous DRAM.

## FAQs
### Q: What does "SDR" stand for in SDR SDRAM?
A: SDR stands for "Single Data Rate," indicating that data is transferred once per clock cycle, unlike DDR (Double Data Rate) which transfers data twice per cycle.

### Q: What are the speed grades of SDR SDRAM?
A: The primary speed ratings are PC66, PC100, and PC133, representing maximum data transfer rates of 66 MHz, 100 MHz, and 133 MHz, respectively.

### Q: How does SDR SDRAM differ from DDR SDRAM?
A: SDR SDRAM transfers data once per clock cycle, while DDR SDRAM transfers data twice per cycle, doubling the bandwidth. DDR SDRAM succeeded SDR SDRAM as a faster, more efficient standard.

## Why It Matters
SDR SDRAM marked a critical advancement in memory technology by synchronizing memory operations with the system clock, resolving timing inefficiencies of earlier asynchronous RAM. This synchronization enabled faster data transfer rates, supporting the performance demands of late 1990s computing. As the first widely adopted synchronous DRAM standard, it laid the groundwork for subsequent technologies like DDR SDRAM, which further increased bandwidth. SDR SDRAM’s speed ratings (e.g., PC133) became industry benchmarks, influencing system design and ensuring compatibility across hardware platforms. Its adoption facilitated smoother multitasking, richer multimedia experiences, and more complex software applications, cementing its role as a foundational technology in the evolution of modern computing.

## Notable For
- **First Synchronous DRAM**: Introduced clock-synchronized memory operations, replacing asynchronous EDO RAM.
- **Single Data Rate Operation**: Transferred data once per clock cycle, establishing baseline performance for later DDR advancements.
- **JEDEC Standardization**: Formalized speed ratings (PC66, PC100, PC133) to ensure industry-wide compatibility.
- **Precursor to DDR**: Served as the technological basis for DDR SDRAM, which doubled data transfer rates per clock cycle.
- **Widespread Adoption**: Became the dominant memory type in late 1990s computers, driving performance improvements in consumer and enterprise systems.

## Body
### Overview
SDR SDRAM is a technical standard for synchronous dynamic random-access memory, designed to coordinate memory operations with the system clock. This synchronization eliminated delays inherent in earlier asynchronous RAM, improving overall system performance.

### Technical Specifications
- **Clock Rates**: Operated at 66 MHz, 100 MHz, or 133 MHz, reflected in speed grades PC66, PC100, and PC133.
- **Voltage**: Required 3.3V power supply, aligning with contemporary hardware standards.
- **Data Transfer**: Single data rate architecture (one transfer per clock cycle).

### History
- **Predecessor**: Replaced Extended Data Output RAM (EDO RAM), which lacked clock synchronization.
- **Successor**: Superseded by DDR SDRAM, which doubled data transfers per clock cycle for higher bandwidth.

### Standards and Form Factors
- **JEDEC Standardization**: Ensured uniformity in speed ratings and compatibility across manufacturers.
- **DIMM Packaging**: Typically deployed in Dual In-line Memory Modules (DIMMs) for desktop and server systems.

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