• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.50-52
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• 2000

페이징 기법의 효율성은 어떠한 페이지 교체 기법을 쓰느냐에 따라 결정된다. LRU 기법은 작업 부하의 변화에 잘 적응하여 많은 경우 좋은 성능을 보인다. 그러나 참조의 횟수에 대한 정보를 이용하지 못한다. LFU 기법은 지역성을 가지는 참조 패턴이 발견되면 좋은 성능을 발휘한다. 그러나 작업 부하가 변하는 경우 이에 적응하지 못한다. 여러 응용에 대해 참조 패턴을 분석하여 보면 참조되는 페이지는 최근성과 참조 횟수에 의해 가치가 결정되며, 따라서 LRU나 LFU 기법 한 가지만으로 페이지 교체 정책을 최적화 시킬 수 없다. 본 논문에서는 LRU 기법과 LFU 기법을 결합한 새로운 교체 기법을 제안한다. 이 교체 기법에서는 LRU 리스트와 LFU 리스트를 결합하여 사용함으로써 참조 시간뿐만 아니라 참조 횟수를 이용하여 페이지들을 교체한다. 트레이스 기반 모의 실험에서는 제안 기법의 순수 LRU 기법보다 나은 성능을 보일 때가 있다.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.151-154
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• 2012

최근 차세대 저장장치로서 비휘발생 플래시 메모리 기반 저장장치의 사용이 층가하고 있다. 본 논문에서는 플래시 메모리 기반 저장장치의 특생인 삭제 연산의 문제점을 고려하는 새로운 버퍼 캐시 교체 기법을 연구하였다. 제안한 클린 블록 우선 (Clean Block First) 기법은 버퍼를 플래시 메모리의 삭제 블록의 리스트로 관리하고 클린 페이지를 가진 블록을 우선적으로 교체하여 플래시 메모리의 삭제 연산 횟수를 줄인다. 트레이스 기반의 시뮬레이션을 수행하여 교체를 위해 검색하는 클린 블록 개수의 변화에 대한 캐시 적중률과 삭제 연산 횟수를 분석하였다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.127-129
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• 2001

본 논문에서는 실시간성을 기반으로 하는 VOD시스템을 위한 우선 순위 가중치 기반의 가상 메모리 교체 기법을 제안하였다. 전통적인 운영체제에서 사용하는 가상 메모리 기법인 LRU와 LFU등은 우선 순위를 전혀 고려하지 않기 때문에 실시간 기반의 운영체제에는 전혀 적합하지 않다. 본 논문에서는 실시간성을 유지하기 위하여 프로세스의 우선 순위에 기반 한 차등화 된 가상 메모리 기법을 제안하였다. 그리고 낮은 우선 순위를 고려하여 주기억장치의 프로세스 공간 점유율도 고려하였다. 실험 결과, 서로 차등화 된 페이지 교체횟수를 보였고 일정한 수준의 우선 순위에 따라서 차등화 된 공간 점유율을 유지하였다.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.88-93
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• 2015

In modern computer systems, DRAM is commonly used as main memory due to its low read/write latency and high endurance. However, DRAM is volatile memory that requires periodic power supply (i.e., memory refresh) to sustain the data stored in it. On the other hand, PCM is a promising candidate for replacement of DRAM because it is non-volatile memory, which could sustain the stored data without memory refresh. PCM is also available for byte-addressable access and in-place update. However, PCM is unsuitable for using main memory of a computer system because it has two limitations: high read/write latency and low endurance. To take the advantage of both DRAM and PCM, a hybrid main memory, which consists of DRAM and PCM, has been suggested and actively studied. In this paper, we propose a novel page replacement algorithm for hybrid main memory. To cope with the weaknesses of PCM, our scheme focuses on reducing the number of PCM writes in the hybrid main memory. Experimental results shows that our proposed page replacement algorithm reduces the number of PCM writes by up to 80.5% compared with the other page replacement algorithms.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.9
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• pp.634-641
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• 2006

Flash memory has many advantages like non-volatility and fast I/O speed, but it has also disadvantages such as not-in-place-update data and asymmetric read/write/erase speed. For the performance of flash memory storage, it is essential for the buffer replacement algorithms to reduce the number of write operations that also affects the number of erase operations. A new buffer replacement algorithm is proposed in this paper, that delays the writes of not-cold-dirty pages in the buffer cache of flash storage. We show that this algorithm effectively decreases the number of write operations and erase operations without much degradation of hit ratio. As a result overall performance of flash I/O speed is improved.

• Journal of Korea Water Resources Association
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• v.40 no.1 s.174
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• pp.39-50
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• 2007

This paper presents applications of the log-linear ROCOF(rate-of-occurrence-of-failure) and the Weibull ROCOF to model the failure rate of individual cast iron pipes in a water distribution system and provides a method of estimating the economically optimal replacement time of the pipes using the 'modified time-scale'. The performance of the two ROCOFs is examined using the maximized log-likelihood estimates of the ROCOFs for the two types of failure data: 'failure-time data' and 'failure-number data'. The optimal replacement time equations for the two models are developed by applying the 'modified time-scale' to ensure the numerical convergence of the estimated values of the model parameters. The methodology is applied to the case study water distribution cast iron pipes and it is found that the log-linear ROCOF has better modeling capability than the Weibull ROCOF when the 'failure-time data' is used. Furthermore, the 'failure-time data' is determined to be more appropriate for both ROCOFs compared to the 'failure-number data' in terms of the ROCOF modeling performances for the water mains under study, implying that recording each failure time results in better modeling of the failure rate than recording failure numbers in some time intervals.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.57-78
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• 2022

The disc cutter and cutterbit, which are the most important factors to increase the excavation efficiency of TBM, are key factors in the design and construction of the cutter head. The arrangement, spacing, number, size, and material of disc cutters suitable for the ground conditions determine the success or failure of TBM construction. The disc cutter, which is a representative consumable part in TBM construction, can cause enormous disruption to the construction cost as well as the construction cost unless accurate prediction of wear and replacement cycle is accompanied. Therefore, in this study, the method of calculating the replacement cycle of the disc cutter calculated at the time of design for the slurry shield TBM field, and the depth of wear and replacement location of the disc cutter that occurred during actual construction were compared by analyzing the field data. For a quantitative comparison, weathered soil/weathered rock, soft rock, and hard rock were classified according to the ground in the section showing constant excavation data, and the trajectory of circle was different depending on the location of the disc cutter, so it was compared and analyzed.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.469-478
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• 2001

In the virtual memory system, page replacement policy exerts a great influence on the performance of demand paging. There are LRU(Least Recently Used) and LFU (Least Frequently Used) as the typical replacement policies. The LRU policy performs effectively in many cases and adapts well to the changing workloads compared to other policies. It however cannot distinguish well between frequently and infrequently referenced pages. The LFU policy requires that the page with the smallest reference count be replaced. Though it considers all the references in the past, it cannot discriminate between references that occurred far back in the past and the more recent ones. Thus, it cannot adapt well to the changing workload. In this paper, we first analyze memory reference patterns of eight applications. The patterns show that the recently referenced pages or the frequently referenced pages are accessed continuously as the case may be. So it is rather hard to optimize page replacement scheme by using just one of the LRU or LFU policy. This paper makes an attempt to combine the advantages of the two policies and proposes a new page replacement policy. In the proposed policy, paging list is divided into two lists (LRU and LFU lists). By keeping the two lists in recency and reference frequency order respectively, we try to restrain the highly referenced pages in the past from being replaced by the LRU policy. Results from trace-driven simulations show that there exists points on the spectrum at which the proposed policy performs better than the previously known policies for the workloads we considered. Especially, we can see that our policy outperforms the existing ones in such applications that have reference patterns of re-accessing the frequently referenced pages in the past after some time.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.4
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• pp.143-148
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• 2017

Flash Memory which is light and strong external shock as storage of small electronics like smartphone, digital camera, car black box has been widely used. Since the operation speed of the read operation and the write operation are different from each other, and the flash memory has the feature that it is not possible to overwrite, the delete operation is added to solve these problems. Wear-leveling must also be considered, since the number of erase times of the flash memory is limited. Many studies have been conducted on the substitutional algorithms of flash memory based on these characteristics of recent flash memories. So, to solve the problem that has existing buffer replacement algorithm this thesis divide page into 6 groups and when proposed algorithm select victim page, it consider reference page frequency and page recency.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.9 no.2
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• pp.81-86
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• 2014

In this paper, a jointly optimal group replacement and spare provisioning policy is presented. Most maintenance policies assume that the spare inventory is always available, but in practice the maintenance schedule is affected by the availability of spare inventory. We present a maintenance-inventory model which jointly optimizes the group replacement interval and spare ordering quantity. Group replacement policy is used when a group of units are put in operation simultaneously. The operating fleet is replaced altogether at a predetermined number of units are failed. A sufficient level of spare inventory is carried to perform a number of group replacement. A cost rate expression which considers the group maintenance cost and inventory holding cost is derived and a heuristic method for searching the optimum value of decision variables is suggested. Numerical examples demonstrate the analytical results and the performance of the presented model.