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Memory Organisation
Published in Pranabananda Chakraborty, Computer Organisation and Architecture, 2020
Paged memory management uses various types of memory allocation policy to operate a virtual memory. Amongst them, demand paging system is one of the most often used policy that properly matches the paging scheme principle. In analogy to the well-known demand feeding algorithm for babies; when the baby cries, you feed it (as opposed to feeding at regular intervals of day). Similarly, in demand paging, pages are brought in memory only when an actual request is issued for a page, and not in advance, i.e. the pages are brought into main memory only upon demand. This policy allows only pages (instead of processes) to be transferred between the main memory and the swap device (virtual memory). The idea of demand paging nicely goes with the concept of working set which is formed only with the pages as being referenced on demand made by the active processes. The major advantage of this method is that it offers the flexibility to dynamically accommodate a larger number of processes within a limited size of physical memory in multiprogramming environment. This, in turn, will substantially increase the system throughput with less overhead (e.g. page fault), and decreases the memory traffic load. Pages of the process not under demand will not involve in this game. This demand paging policy was first implemented in UNIX BSD 4.0 release. Later, UNIX System V and many other modern operating systems also employed this demand-paging scheme in their memory management.
D
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
DeMorgan's theorem indicates a rising slope of the input signal. A "0" indicates a falling slope of the input signal. The sampling rate is dependent on the derivative of the signal, since a rapidly changing signal would require a rapid sampling rate for acceptable performance. delta modulation control a pulse-time modulation method transplanted from the delta modulation in signal processing. The difference between the control reference and the switched signal is integrated and fed to a Schmitt trigger. When the integrated value reaches a predefined upper bound the switch is turned off. When the integrated value reaches a predefined lower bound the switch is turned on. delta rule a supervised learning algorithm, based upon gradient descent, that was developed for application to single-layer networks of linear threshold units. For each input pattern x, the weight wi j connecting input x j to unit i is adjusted according to Dwi j = h(ti - wi · x)x j, where wi is the vector of weights wi j, ti is the target output for unit i, and h is a positive constant. This rule is also known as the Widrow-Hoff rule and the LMS algorithm. delta-delta transformer a three-phase transformer connection formed by connecting three single-phase transformers in which the windings on both the primary and the secondary sides are connected in series to form a closed path. delta-wye transform a transformation between delta and wye connections. delta-wye transformer a three-phase transformer connection formed by connecting three single-phase transformers in which the primary windings are connected in series to form a closed path while one end of each of the secondary windings is connected to a common point (the neutral). demagnetization the act of removing a device from being in a magnetic state, i.e., rearranging the atomic magnetic domains in a disoriented fashion. demagnetizing field the magnetic field produced by divergences in the magnetization of a magnetic sample. demand assign multiple access protocol telephone signalling mechanism in which the access is established for the duration of a call. demand fetch in a cache memory, the name given to fetching a line from the memory into the cache on a cache miss when it is requested and not before. demand meter an electric meter which shows both the energy used and the peak power demand in a given period. demand paging condition where each page in virtual memory is loaded into main memory, after first being referenced by the processor (i.e., not in advanced). The first reference to each page will thus always cause a "page fault" (page not in main memory). After these initial page faults, most of the pages needed by the program are in main memory. demodulation the process by which a modulated signal is recovered back to its original form. It is the general process of extracting the information-bearing signal from another signal. Modulation is the general process of embedding an information-bearing signal into a second carrier signal. An important objective in modulation is to produce a signal whose frequency range is suitable for transmission over the communication channel to be used. See also modulation. DeMorgan's theorem a formula for finding the complement of a Boolean expression. It has two forms: (1) A B = A B (2) A B = A B
A mathematical multi-dimensional mechanism to improve process migration efficiency in peer-to-peer computing environments
Published in Cogent Engineering, 2018
Ehsan Mousavi Khaneghah, Reyhaneh Noorabad Ghahroodi, Amirhosein Reyhani ShowkatAbad
Class I includes time-related parameters, migration costs, and process-related properties. The parameters that are important in choosing the process migration strategy because of the main reason of creating different processes include the reducing freeze time (Jianjun et al., 2015; Medina & García, 2014). They are defined below:Initialtime: The time spent during the process starting from migration until it again resumes its execution on the destination machine.Totaltime: The time spent during the process starting from migration until the whole information of the process has been sent to the destination machine.Freezetime: It is the duration when the process is suspended and the migrated process cannot respond to the requirements.Migratecost: It refers to the costs of transferring the state of a process.Memory Migratecost: It refers to the cost demand paging from process address space.IPCtype: It chooses the strategy that is both suitable and influential.Class II involves locality properties, which indicate the dependency of the migrated process to the source machine. These properties are commonly named as “residual dependency,” and it means that some parts of process information will stay on the source machine even when the process migration is completed. In this case, this machine can recover the process using the remaining information on the source machine whenever the destination machine fails (Medina & García, 2014).