Racetrack memory (RM), a new storage scheme in which information flows along a nanotrack, has been considered as a potential candidate for future high-density storage device instead of hard disk drive (HDD). The first RM technology, which was proposed in 2008 by IBM, relies on a train of opposite magnetic domains separated by domain walls (DWs), named DW-RM. After 10 years of intensive research, a variety of fundamental advancements has been achieved; unfortunately, no product has been available until now. With increasing effort and resources dedicated to the development of DW-RM, it is likely that new materials and mechanisms will soon be discovered for practical applications. However, new concepts might also be on the horizon. Recently, an alternative information carrier, magnetic skyrmion, which was experimentally discovered in 2009, has been regarded as a promising replacement of DW for RM, named skyrmion-based RM (SK-RM). Intensive effort has been involved and amazing advances have been made in observing, writing, manipulating, and deleting individual skyrmions. So, what is the relationship between DW and skyrmion? What are the key differences between DW and skyrmion, or between DW-RM and SK-RM? What benefits could SK-RM bring and what challenges need to be addressed before application? In this review article, we intend to answer these questions through a comparative cross-layer study between DW-RM and SK-RM. This work will provide guidelines, especially for circuit and architecture researchers on RM.

The well-known empirical phenomenon known as Moore's Law has held true for the past half century. However, it is beginning to break down, owing to limitations arising from leakage currents caused by the quantum effect. As a result, the search for alternatives or complementary technologies that can aid the downscaling of complementary metal-oxide-semiconductor (CMOS) technology has been accelerated in the field of electronics. Among various potential candidates, spintronic technology has attracted considerable interest and attention, especially for the topological spin textures known as magnetic skyrmions. Magnetic skyrmions are expected to have topologically protected stability and nanoscale size, and require a very low driving current density, therefore they are considered as potential building blocks for future spintronic devices and integrated circuits. Furthermore, recent experimental demonstrations of the control of individual nanometer-scale skyrmions, including their creation, detection, transportation, and manipulation at room temperature, further highlight their potential for future electronic applications. In this paper, we review the current status and outlook of skyrmions from the viewpoint of electronic applications. First, the fundamental and elementary functionality of skyrmions, such as electric write-in, read-out, transmission, and manipulation, are introduced. Then, potential electronic applications of skyrmions for nonvolatile memory and logic circuits are described with case studies. Finally, we conclude with an analysis of current challenges, limitations, and future trends of skyrmion research.