X-ray: Discovering DRAM Internal Structure and Error Characteristics by Issuing Memory Commands

TL;DR

This paper uncovers detailed internal structures and error behaviors of DRAM using experimental techniques, providing new insights into DRAM operation, reliability, and vulnerabilities like rowhammer.

Contribution

It reveals the size, structure, and operation of DRAM subarrays and clarifies the causes of activate-induced bitflips and rowhammer, which were previously misunderstood.

Findings

Identified the size and structure of DRAM subarrays.

Corrected misconceptions about activate-induced bitflips.

Supported the cause of rowhammer with experimental evidence.

Abstract

The demand for accurate information about the internal structure and characteristics of dynamic random-access memory (DRAM) has been on the rise. Recent studies have explored the structure and characteristics of DRAM to improve processing in memory, enhance reliability, and mitigate a vulnerability known as rowhammer. However, DRAM manufacturers only disclose limited information through official documents, making it difficult to find specific information about actual DRAM devices. This paper presents reliable findings on the internal structure and characteristics of DRAM using activate-induced bitflips (AIBs), retention time test, and row-copy operation. While previous studies have attempted to understand the internal behaviors of DRAM devices, they have only shown results without identifying the causes or have analyzed DRAM modules rather than individual chips. We first uncover the size, structure, and operation of DRAM subarrays and verify our findings on the characteristics of DRAM. Then, we correct misunderstood information related to AIBs and demonstrate experimental results supporting the cause of rowhammer. We expect that the information we uncover about the structure, behavior, and characteristics of DRAM will help future DRAM research.