• 한국정보과학회논문지:시스템및이론
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• 제36권6호
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• pp.521-531
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• 2009

플래시 메모리는 하드디스크와 다른 물리적 특성을 가진다. 대표적으로 읽기연산과 쓰기연산의 비용이 다르고, 덮어쓰기(overwrite)가 불가능하여 소거연산(erase)이 선행되어야 한다. 이러한 물리적 제약을 소프트웨어적으로 보완해주기 위해서, 플래시 메모리를 사용하는 시스템은 대부분 플래시 변환 계층(Flash Translation Layer)을 사용한다. 현재까지 효율적인 FTL 기법들이 제안되었으며, 이들은 임의쓰기(random writes) 패턴보다 순차쓰기(sequential writes) 패턴에 훨씬 더 효율적으로 동작한단. 본 논문에서는 플래시 메모리 상에서 B-트리 인덱스를 효율적으로 생성, 유지하기 위한 새로운 기법을 제안한다. B-트리에 키의 삽입, 삭제, 수정 등치 연산을 수행하면 FTL에 비효율적인 임의쓰기 패턴을 많이 발생시키며, 결국 B-트리 인덱스 유지 비용이 커지게 된다. 제안하는 기법에서는 B-트리에서 발생되는 임의쓰기 패턴을 먼저 플래시 메모리의 쓰기 버퍼에 추가쓰기(append writes) 패턴으로 변환하여 저장하고, 추후 이를 FTL에 효율적인 순차쓰기 패턴으로 FTL에 전달한다. 다양한 실험을 통해 제안하는 기법이 기존의 기법보다 플래시 메모리 I/O 비용 측면에서 우수하다는 것을 보인다.

• 정보과학회 논문지
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• 제42권2호
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• pp.183-189
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• 2015

최근 DRAM 기반의 메인 메모리 기술 발전이 한계에 봉착함에 따라 컴퓨터 시스템의 진보에도 어려움이 발생하고 있다. 이를 개선하기 위해 집적도가 높고 비휘발성을 갖는 차세대 메모리 기술이 등장하고 있으나 이들은 쓰기 속도가 느리거나 쓰기 횟수에 제한이 있는 등, 메인 메모리로 사용하기에는 아직 무리가 있다. 본 논문에서는 여러 차세대 메모리 기술들의 장점들을 조합하여 활용하는 하이브리드 메인 메모리 시스템, 즉 HyMN을 제안한다. HyMN은 차세대 메모리 기술을 쓰기적합램과 읽기적합램으로 분류하여 메인 메모리 시스템을 구성함으로써, 내구성이 양호하고, 고용량화가 용이하며, 비휘발성을 활용할 수 있는 시스템을 구현한다. 본 논문에서는 또한, 쓰기적합램이 어느 정도의 크기로 구성되어야 하는지를 보이고 정전 시 손실에 대한 복구비용이 없거나 미미한 HyMN이 일상적으로 프로세스를 실행할 때 실행 시간 성능이 DRAM으로만 구성된 시스템에 비하여 유사함을 검증한다.

• 한국컴퓨터정보학회논문지
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• 제25권2호
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• pp.21-29
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• 2020

IT 산업 환경에서 모바일 데이터의 수요 증가로 인해 NAND 플래시 메모리의 사용이 지속적으로 증가하고 있다. 하지만, 플래시 메모리의 소거 동작은 긴 대기 시간과 높은 소비 전력을 요구하여 각 셀의 수명을 제한한다. 따라서 쓰기와 삭제 작업을 자주 수행하면 플래시 메모리의 성능과 수명이 단축된다. 이런 문제를 해결하기 위해 디스크 버퍼를 이용, 플래시 메모리에 할당되는 쓰기 및 지우기 연산을 감소시켜 플래시 메모리의 성능을 향상시키는 기술이 연구되고 있다. 본 논문에서는 쓰기 횟수를 최소화하기 위한 CPWL 기법을 제안한다. CPWL 기법은 버퍼 메모리 액세스 패턴에 따라 읽기 및 쓰기 페이지를 나누어 관리한다. 이렇게 나뉜 페이지를 정렬하여 쓰기 횟수를 줄이고 결과적으로 플래시 메모리의 수명을 늘리고 에너지 소비를 감소시킨다.

• Korean Journal of Radiology
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• 제1권1호
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• pp.19-24
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• 2000

Objective: In order to investigate the functional brain anatomy associated with verbal and visual working memory, functional magnetic resonance imaging was performed. Materials and Methods: In ten normal right handed subjects, functional MR images were obtained using a 1.5-T MR scanner and the EPI BOLD technique. An item recognition task was used for stimulation, and during the activation period of the verbal working memory task, consonant letters were used. During the activation period of the visual working memory task, symbols or diagrams were employed instead of letters. For the post-processing of images, the SPM program was used, with the threshold of significance set at p < .001. We assessed activated brain areas during the two stimulation tasks and compared the activated regions between the two tasks. Results: The prefrontal cortex and secondary visual cortex were activated bilaterally by both verbal and visual working memory tasks, and the patterns of activated signals were similar in both tasks. The superior parietal cortex was also activated by both tasks, with lateralization to the left in the verbal task, and bilaterally without lateralization in the visual task. The inferior frontal cortex, inferior parietal cortex and temporal gyrus were activated exclusively by the verbal working memory task, predominantly in the left hemisphere. Conclusion: The prefrontal cortex is activated by two stimulation tasks, and this is related to the function of the central executive. The language areas activated by the verbal working memory task may be a function of the phonological loop. Bilateral prefrontal and superior parietal cortices activated by the visual working memory task may be related to the visual maintenance of objects, representing visual working memory.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.281-284
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• 2004

Photo-induced memory effect of an organic light-emitting diode(OLED) composed of a hydrazone-derivative(DBAH) dispersed in bis-phenol-A type polycarbonate polymer(PCA) in the presence of thio-Michler's ketone, was investigated by the measuring of the current density and luminance at the various conditions. After the light exposure, the current of the OLED was decreased approximately one order, and the luminance of the OLED also decresed. This memory effct was erasable by heating the OLED to the temperature higher than the glass transition temperature(Tg). As shown in this result, we found the memory effect was erased by heating and returned to its original state in the hole injecting layer(HIL) of the OLED. A series of these phenomena was suggested the possibility of the application to the imaging plate.

• 한국광학회:학술대회논문집
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• 한국광학회 1990년도 제5회 파동 및 레이저 학술발표회 5th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.102-111
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• 1990

In this thesis, an optical bidirectional inner-product associative memory model using liquid crystal television is proposed and analyzed theoretically and realized experimentally. The LCTV is used as a SLM(spatial light modulator), which is more practical than conventional SLMs, to produce image vector in terms of computer and CCD camera. Memory and input vectors are recorded into each LCTV through the video input connectors of it by using the image board. Two multi-focus hololenses are constructed in order to perform optical inner-product process. In forward process, the analog values of inner-products are measured by photodetectors and are converted to digital values which are enable to control the weighting values of the stored vectors by changing the gray levels of the pixels of the LCTV. In backward process, changed stored vectors are used to produce output image vector which is used again for input vector after thresholding. After some iterations, one of the stored vectors is retrieved which is most similar to input vector in other words, has the nearest hamming distance. The experimental results show that the proposed inner-product associative memory model can be realized optically and coincide well with the computer simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 심포지엄 논문집 정보 및 제어부문
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• pp.267-269
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• 2006

Recently, flash memories are one of best media to support portable computer's storages in mobile computing environment. The features of non-volatility, low power consumption, and fast access time for read operations are sufficient grounds to support flash memory as major database storage components of portable computers. However, we need to improve traditional Indexing scheme such as B-Tree due to the relatively slow characteristics of flash operation as compared to RAM memory. In order to achieve this goal, we devise a new indexing scheme called F-Tree. F-Tree improves tree operation performance by compressing pointers and keys in tree nodes and rewriting the nodes without a slow erase operation in node insert/delete processes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1994년도 추계학술대회 논문집
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• pp.33-36
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• 1994

The characteristics of the nonvolatile MONOS memory devices as the nitride thickness is scaled down while maintaining constant tunneling oxide thickness and blocking oxide thickness have been investigated in order to obtain the 5V-programmable E$^2$PROM. We have found that 1V memory window for a 5V programming voltage and 10 year data retention can be achieved in the scaled MONOS memory devices with a 50 blocking oxide, a 57 nitride and a 19 tunneling oxide.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.117-120
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• 2005

The SONOS devices have been fabricated by the conventional $0.35{\mu}m$ complementary metal-oxide-semiconductor (CMOS) process with NOR array. Two-bit operation using conventional process achieve the high density memory compare with other two-bit memory. Lateral diffusion phenomenon in the two-bit operation cause soft error in the memory. In this study, the programming conditions arc investigated in order to reduce lateral diffusion for two-bit operation of CSL-NOR type SONOS flash cell.

• 한국전기전자재료학회논문지
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• 제11권1호
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• pp.57-61
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• 1998

In this study, PLZT stock solutions were prepared by Sol-Gel processing after the compositions were selected in the memory region of PLZT bulk phase diagram. PLZT solutions were deposited on the ITO glass substrate by spin-coating method. The thin films were annealed by rapid thermal processing. The electric characteristics, hysteresis loop, C-V characteristics of thin films in the memory region were measured in order to investigate the electrical characteristics of PLZT thin films. In selected compositions the decrease in Zr/Ti ratio led to an increase in dielectric constant and the decrease in remanent polarization and coercieve field which brought about slim hysteresis loop.