Current computer systems fill the demand of operating systems and applications for ever greater amounts of random access memory by paging the least recently used data to the hard disk drive. This paging process is called "virtual memory," to indicate that the hard disk drive is used to create the illusion that the computer has more random access memory than it actually has. Unfortunately, the fastest hard disk drives are over five orders of magnitude slower than the DRAM they are emulating. When the demand for memory increases to the point that processes are being continually saved to disk and then retrieved again, a process called "thrashing" occurs, and the performance of the entire computer system plummets. This thesis sought to find alternatives for home and small business computer users to the hard disk drive for virtual memory which would not suffer from the same long delays. Virtual memory is especially important for older computers, which often are limited by their motherboards, their processors and their power supplies to a relatively small amount of random access memory. Thus, this thesis was focused on improving the performance of older computers by replacing the hard disk drive with faster technologies for the virtual memory. Of the different technologies considered, flash memory was selected because of its low power requirements, its ready availability, its relatively low cost and its significantly faster random access times. Two devices were evaluated on a system with a 512MB of RAM, a Pentium 4 processor and a SATA hard disk drive. Theoretical models and a simulator were developed, and physical performance measurements were taken. Flash memory was not shown to be significantly faster than the hard disk drive in virtual memory applications.

Iron-cobalt alloys have been extensively studied as potential hard disk drive write head materials due to their potentially high saturation flux densities (~2.4T), low coercivities and ease of deposition. Iron-cobalt plating solutions have, however, been shown to have stability issues, necessitating that they be used at low pH or that a stabilizing agent be added to the solution. The purpose of this thesis is to evaluate the stability of a dibasic ammonium citrate plating solution and to characterize the deposits which result from its use. The plating solutions are found to be less stable than previously claimed. The solutions are oxidized by dissolved oxygen, which leads to a valence change in the iron ions and eventually the formation of iron oxide/hydroxide precipitates. These effects are exacerbated by heating or the application of a voltage across the solution. Deposits plated from the solution are fine grained (<40nm) and compact through their thickness. While normally deposited as the equilibrium BCC phase, metastable phases are deposited at elevated temperatures, high pH or in the absence of a stabilizing agent. A metastable phase which is isomorphous to α-Mn is deposited at elevated temperatures. This phase transforms to the BCC phase when annealed at >174ºC and is highly textured. Its presence is detrimental to deposit coercivity. / Materials Engineering

No description available.

The thesis aims at verification of using emerging Solid-State drives in disk arrays. The advent of SSD disks caused a small revolution in area of data storage, because the growth performance of hard drives has been slow compared to other PC components. But an entirely different principle of operation could mean compatibility problems between SSD and related technologies, such as RAID. This thesis aims at analyzing all the relevant technologies, mainly HDD, SSD and RAID. To achieve this objective, information from literature, articles and other appropriate sources will be used. Other objectives of this thesis are to determine how much are the SSDs suitable for use in the disk array, because low performance RAID controllers or different principles of operation could limit their efficiency. This question should be answered by submission of selected types of storage arrays to synthetic and practical tests of performance. The final goal is to use financial analysis of the test solutions as a shared file storage. Today, remote access to data is used by a wide range of job positions. Slow storage could mean inefficient use of working time and therefore unnecessary financial costs. The goal of my work is primarily to provide answers to the questions mentioned above. Currently it is very hard to find tests of more complex forms of disk arrays based on solid-state drives. This article can be also very useful for companies where fileservers are used to share user data. Based on the result of cost analysis, the company can then decide what type of storage is best for its purpose.

This thesis concerns the control of an adaptive passive vibration neutralizer and the feasibility of miniaturizing this type of tunable vibration neutralizer for small-scale applications. An analytical model for the adaptive passive vibration neutralizer is derived and compared to experimental results. A tuning algorithm is derived from a curve-fit of experimental tests on the specific neutralizer. A more generic tuning algorithm is also developed, which does not require testing of the neutralizer for optimal control. Both tuning algorithms are tested using a chirp forcing function to simulate drift in the excitation frequency of a host structure. Computer simulation and experimental results are given for these tests. A novel low-cost, small-scale vibration neutralizer is constructed from packing bubble-wrap. Analytical models for the stiffness are calculated, and experimental data is used to derive a damped mass-spring model. Miniaturization of vibration neutralizers is described, and many of the pitfalls in design are discussed. Theoretical tuning frequencies of possible adaptive passive vibration neutralizers at different scales are included. The goal for these miniaturized vibration neutralizers is vibration control in computer hard drives. A hard drive is analyzed for vibration problems. Included are plots of the velocities of the read-write head and spindle. Limitations of the measurement equipment are discussed, and directions for future work on small-scale tunable vibration neutralizers are outlined. / Master of Science

No description available.

Magnetic recording media refers to the disc shaped thin film magnetic medium present inside the hard disk drive of a computer. Magnetic recording is an important function of the hard disk drive by which information such as text, pictures, audio and videos are stored. Information is broken down to a simple binary format and is stored as magnetised bits along the tracks of the disk forming the hard drive. Over the years advancements in research on the type of magnetic materials used has allowed increased data storage capacities by reducing magnetic bit sizes. It is with this advancement in magnetic data storage, that we have today's hard disk drive technology, which uses a perpendicular magnetic medium to store data. A perpendicular magnetic medium is a multi-layered magnetic thin film structure with the topmost layer comprising nanoscale magnetic grains of high perpendicular anisotropy. The topmost recording layer (RL) is mapped into individual bits of 80-100 nm² area that consist of 5-10 nm diameter CoCrPt grains, embedded in an oxide matrix. A bit area is defined to ensure a significant number of stable grains allowing data to be stored in each bit as a ‘0' or a ‘1' depending on its switched magnetic state. The magnetic grains if sputtered below a threshold grain size tend to suffer from thermal fluctuation and instability due to super-paramagnetic effects, hence bringing limitations to grain size. As a result of this, research in recent years has been directed at introducing a softer magnetic exchange coupled composite (ECC) layer above the recording layer. This layer facilitates the delicate balance of switching smaller grains with strong magneto-crystalline anisotropy at lower magnetic fields, by exchange coupling with the CoCrPt grains in the recording layer. However this technique of increasing the efficiency in the perpendicular magnetic medium by introducing ‘facilitating' layers is an area that is still being widely researched and understood. Although numerous surface and bulk analysis techniques exist to study magnetic and surface properties of these materials, there is limited information on the structural and magnetic properties of these materials at the nanoscale level. The reported work investigates the structural and magnetic properties of the magnetic grains and multi-layers in the perpendicular magnetic medium using polarised neutron scattering and reflectivity techniques. The work investigates the structural and magnetic properties of the CoCrPt grains, apart from understanding the CoCrPt magnetic grain switching. The work also investigates the magnetisation in the layers of the thin film perpendicular media structure using polarised neutron reflectivity (PNR). Using polarised small angle neutron scattering (PolSANS), it has been shown that ferromagnetic ordered core region of the CoCrPt grain in the recording layer is smaller than the physical CoCrPt granular structure. The magnetic switching behaviour of the CoCrPt grain at different magnetic fields is also analysed and the experimental PolSANS data is fitted with non-interacting size-dependent analytical grain switching models. This result provides significant evidence that the magnetic anisotropy increases with grain size, with larger magnetic grains having larger magnetic anisotropy. Polarised neutron scattering experiments are carried out with the magnetically softer exchange coupled composite (ECC) layer included in the thin film magnetic structure. The first experiments investigate if the ECC layer contributes to the nuclear and magnetic interference scattering term in the experimenting scattering data. The experiments clearly show that there is no contribution from the ECC layer in the nuclear and magnetic scattering interference term. The role of the ECC layer in the magnetic switching process is then investigated at different magnetic fields. The ECC layer was found to influence the size-dependent magnetic grain switching of the CoCrPt grains in the recording layer and a detailed investigation is presented in the reported work. Polarised neutron reflectivity (PNR) experiments have also been carried out with the ECC layer on the perpendicular magnetic media samples. These experiments investigate the composition and thickness of the thin film structure, while also providing information on the magnetic state of the thin films under the influence of an in-plane magnetic field. The in-plane magnetisation in the recording and ECC layer is determined at different in-plane magnetic fields. The magnetisation values determined for the ECC layer and the recording layer (RL) at different in-plane magnetic fields help better understand the differences in their magnetic properties.

This dissertation presents design and implementation of continuous time analog filters for two specific applications: wideband analog systems such as disk drive channel and low-power wireless applications. Specific focus has been techniques that reduce the power requirements of the overall system either through improvement in architecture or efficiency of the analog building blocks. The first problem that this dissertation addresses is the implementation of wideband filters with high equalization gain. An efficient architecture that realizes equalization zeros by combining available transfer functions associated with a biquadratic cell is proposed. A 330MHz, 5th order Gm-C lowpass Butterworth filter with 24dB boost is designed using the proposed architecture. The prototype fabricated in standard 0.35um CMOS process shows -41dB of IM3 for 250mV peak to peak swing with 8.6mW/pole of power dissipation. Also, an LC prototype implemented using similar architecture is discussed in brief. It is shown that, for practical range of frequency and SNR, LC based design is more power efficient than a Gm-C one, though at the cost of much larger area. Secondly, a complementary current mirror based building block is proposed, which pushes the limits imposed by conventional transconductors on the powerefficiency of Gm-C filters. Signal processing through complementary devices provides good linearity and Gm/Id efficiency and is shown to improve power efficiency by nearly 7 times. A current-mode 4th order Butterworth filter is designed, in 0.13um UMC technology, using the proposed building. It provides 54.2dB IM3 and 55dB SNR in 1.3GHz bandwidth while consuming as low as 24mW of power. All CMOS filter realization occupies a relatively small area and is well suited for integration in deep submicron technologies. Thirdly, a 20MHz, 68dB dynamic range active RC filter is presented. This filter is designed for a ten bit continuous time sigma delta ADC architecture developed specifically for fine-line CMOS technologies. Inverter based amplification and a common mode feedback for such amplifiers are discussed. The filter consumes 5mW of power and occupies an area of 0.07 mm2.

In the past years solid state disks have developed drastically and are now gaining increased popularity compared to conventional hard drives. While hard disk drives work predictable, transparent SSD routines work in the background without the user’s knowledge. This work describes the changes to the everyday life for forensic specialists; a forensic investigation includes data recovery and the gathering of a digital image of each acquired memory that provides proof of integrity through a checksum. Due to the internal routines, which cannot be stopped, checksums are falsified. Therefore the images cannot prove integrity of evidence anymore. The report proves the inconsistence of checksums of SSD and shows the differences in data recovery through high recovery rates on hard disk drives while SSD drives scored no recovery or very poor rates.

This thesis aims to present solutions to improve the performance of SQLite library on mobile systems. In particular, two approaches are presented to add lightweight locking mechanisms to the SQLite library and improve concurrency of the SQLite library on Android operating system. The impact on performance is discussed after each section. Many applications on the Android operating system rely on the SQLite library to store ordered data. However, due to heavy synchronization primitives used by the library, it becomes a performance bottleneck for applications which push large amount of data into the database. Related work in this area also points to SQLite database as one of the factors for limiting performance. With increasing network speeds, the storage system can become a performance bottleneck, as applications download larger amounts of data. The following work in this thesis addresses these issues by providing approaches to increase concurrency and add light-weight locking mechanisms. The factors determining the performance of Application Programming Interfaces provided by SQLite are first gathered from IO traces of common database operations. By analyzing these traces, opportunities for improvements are noticed. An alternative locking mechanism is added to the database file using byte-range locks for fine-grained locking. Its impact on performance is measured using SQLite benchmarks as well as real applications. A multi-threaded benchmark is designed to measure the performance of fine grained locking in multi-threaded applications using common database operations. Recent versions of SQLite use write ahead logs for journaling. We see that writes to this sequential log can occur concurrently, especially in flash drives. By adding a sequencing mechanism for the write ahead log, the writes can proceed simultaneously. The performance of this method is also analyzed using the synthetic benchmarks and multi-threaded benchmarks. By using these mechanisms, the library is observed to gain significant performance for concurrent writes.