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Virtual Memory Compression
Virtual memory compression (also referred to as RAM compression and memory compression) is a memory management technique that utilizes data compression to reduce the size or number of paging requests to and from the auxiliary storage. In a virtual memory compression system, pages to be paged out of virtual memory are compressed and stored in physical memory, which is usually random-access memory (RAM), or sent as compressed to auxiliary storage such as a hard disk drive (HDD) or solid-state drive (SSD). In both cases the virtual memory range, whose contents has been compressed, is marked inaccessible so that attempts to access compressed pages can trigger page faults and reversal of the process (retrieval from auxiliary storage and decompression). The footprint of the data being paged is reduced by the compression process; in the first instance, the freed RAM is returned to the available physical memory pool, while the compressed portion is kept in RAM. In the second instance, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management
Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of Resource management (computing), resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. This is critical to any advanced computer system where more than a single Process (computing), process might be underway at any time. Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of Random-access memory, RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have an extensive effect on overall system C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Connectix
Connectix Corporation was a software and hardware company that released innovative products that were either made obsolete as Apple Computer incorporated the ideas into system software, or were sold to other companies once they became popular. It was formed in October 1988 by Jon Garber; the dominant board members and co-founders were Garber, Bonnie Fought (the two were later married), and close friend Roy McDonald. McDonald was still Chief Executive Officer and president when Connectix finally closed in August 2003. Products Primary products included these: * Virtual: Its original flagship product, which introduced virtual memory to the Macintosh operating system, Classic Mac OS, Mac OS, years before Apple's implementation in System 7. Virtual also runs on a motley assortment of accelerator cards for the original Mac, Mac Plus, and Mac SE, which were not supported by Apple. * HandOff II: The file launcher developed by Fred Hollander of Utilitron, Inc. This INIT for Macintosh s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Least Recently Used
In computing, cache replacement policies (also known as cache replacement algorithms or cache algorithms) are Program optimization, optimizing instructions or algorithms which a computer program or hardware-maintained structure can utilize to manage a cache (computing), cache of information. Caching improves performance by keeping recent or often-used data items in memory locations which are faster, or computationally cheaper to access, than normal memory stores. When the cache is full, the algorithm must choose which items to discard to make room for new data. __TOC__ Overview The average memory reference time is : T = m \times T_m + T_h + E where : m = miss ratio = 1 - (hit ratio) : T_m = time to make main-memory access when there is a miss (or, with a multi-level cache, average memory reference time for the next-lower cache) : T_h= latency: time to reference the cache (should be the same for hits and misses) : E = secondary effects, such as queuing effects in multiprocessor sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thrashing (computer Science)
In computer science, thrashing occurs in a system with virtual memory when a computer's real storage resources are ''overcommitted'', leading to a constant state of paging and page faults, slowing most application-level processing. This causes the performance of the computer to degrade or even collapse. The situation can continue indefinitely until the user closes some running applications or the active processes free up additional virtual memory resources. After initialization, most programs operate on a small number of code and data pages compared to the total memory the program requires. The pages most frequently accessed at any point are called the working set, which may change over time. When the working set is not significantly greater than the system's total number of real storage ''page frames'', virtual memory systems work most efficiently, and an insignificant amount of computing is spent resolving page faults. As the total of the working sets grows, resolving page fa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process (computing)
In computing, a process is the Instance (computer science), instance of a computer program that is being executed by one or many thread (computing), threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions Concurrency (computer science), concurrently. While a computer program is a passive collection of Instruction set, instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same progra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
I/O-bound
In computer science, I/O bound refers to a condition in which the time it takes to complete a computation is determined principally by the period spent waiting for input/output operations to be completed, which can be juxtaposed with being CPU bound. This circumstance arises when the rate at which data is requested is slower than the rate it is consumed or, in other words, more time is spent requesting data than processing it. I/O bound as an inherent problem in computing The I/O bound state has been identified as a problem in computing almost since its inception. The Von Neumann architecture, which is employed by many computing devices, this involves multiple possible solutions such as implementing a logically separate central processor unit which along with storing the instructions of the program also retrieves actual data usually from main memory and makes use of this more accessible data for working. When the process is terminated it writes back the results to the original st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Compression
A disk compression software utility increases the amount of information that can be stored on a hard disk drive of given size. Unlike a file compression utility, which compresses only specified files—and which requires the user to designate the files to be compressed—an on-the-fly disk compression utility works automatically through resident software without the user needing to be aware of its existence. On-the-fly disk compression is therefore also known as transparent, real-time or online disk compression. When information needs to be stored to the hard disk, the utility compresses the information. When information needs to be read, the utility decompresses the information. A disk compression utility overrides the standard operating system routines. Since all software applications access the hard disk using these routines, they continue to work after disk compression has been installed. Disk compression utilities were popular especially in the early 1990s, when micr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Compression Ratio
Data compression ratio, also known as compression power, is a measurement of the relative reduction in size of data representation produced by a data compression algorithm. It is typically expressed as the division of uncompressed size by compressed size. Definition Data compression ratio is defined as the ratio between the ''uncompressed size'' and ''compressed size'': : = \frac Thus, a representation that compresses a file's storage size from 10 MB to 2 MB has a compression ratio of 10/2 = 5, often notated as an explicit ratio, 5:1 (read "five" to "one"), or as an implicit ratio, 5/1. This formulation applies equally for compression, where the uncompressed size is that of the original; and for decompression, where the uncompressed size is that of the reproduction. Sometimes the ''space saving'' is given instead, which is defined as the reduction in size relative to the uncompressed size: : = 1 - \frac Thus, a representation that compresses the storage size of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embedded Device
An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or Electronics, electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. , it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems. Modern embedded systems are often based on microcontrollers (i.e. microprocessors with integrated memory and peripheral interfaces), but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also common, especially in more complex systems. In either case, the proc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
WKdm
WKDM (1380 AM) is a commercial radio station licensed to New York, New York. The station is owned by Multicultural Broadcasting and broadcasts in Mandarin Chinese on weekdays. Most shows are brokered programming, where the host pays for the time and may sell commercials to support the broadcasts. On weekends, programming switches to Spanish language Christian radio. WKDM operates at 5,000 watts by day, using a directional antenna to protect other stations on 1380 AM. After being granted a Federal Communications Commission (FCC) construction permit to increase night power, it operates at 13,000 watts after sunset, using a different directional pattern. The station's transmitter is located in Carlstadt, New Jersey. History The station began operation in 1926, as WKBQ. The original call sign was randomly assigned from a sequential roster of available call letters. One of the station's first permanent homes was inside Starlight Park, an amusement park located on the east bank ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LZ4 (compression Algorithm)
LZ4 is a lossless data compression algorithm that is focused on compression and decompression speed. It belongs to the LZ77 family of byte-oriented compression schemes. Features The LZ4 algorithm aims to provide a good trade-off between speed and compression ratio. Typically, it has a smaller (i.e., worse) compression ratio than the similar LZO algorithm, which in turn is worse than algorithms like DEFLATE. However, LZ4 compression speed is similar to LZO and several times faster than DEFLATE, while decompression speed is significantly faster than LZO. Design LZ4 only uses a dictionary-matching stage (LZ77), and unlike other common compression algorithms does not combine it with an entropy coding stage (e.g. Huffman coding in DEFLATE). The LZ4 algorithm represents the data as a series of sequences. Each sequence begins with a one-byte token that is broken into two 4-bit fields. The first field represents the number of literal bytes that are to be copied to the output. The s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lempel–Ziv–Oberhumer
Lempel–Ziv–Oberhumer (LZO) is a lossless data compression algorithm that is focused on decompression speed. Design The original "lzop" implementation, released in 1996, was developed by Markus Franz Xaver Johannes Oberhumer, based on earlier algorithms by Abraham Lempel and Jacob Ziv. The LZO library implements a number of algorithms with the following characteristics: * Higher compression speed compared to DEFLATE compression * Very fast decompression * Requires an additional buffer during compression (of size 8 kB or 64 kB, depending on compression level) * Requires no additional memory for decompression other than the source and destination buffers * Allows the user to adjust the balance between compression ratio and compression speed, without affecting the speed of decompression LZO supports overlapping compression and in-place decompression. As a block compression algorithm, it compresses and decompresses blocks of data. Block size must be the same for comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
