Annotated ES5. Annotated ECMAScript 5. An auto- generated. HTML version is available, too: http: //ecma- international. This is an annotated, hyperlinked, HTML version of Edition 5. ECMAScript Specification. A. key to the markers explains the different types. However, this document itself may not. Ecma International, except as needed for the. Ecma. International. The. limited permissions are granted through the standardization phase. Ecma International or its successors or. This. document and the information contained herein is provided on an . The. language was invented by Brendan Eich at Netscape and first appeared. Do More Than Create Web Pages Do more than 'learn how.' Do more than merely putting up yet another site or blog that 'sits there.' Start and build a real business. It has appeared in all. Netscape and in all browsers from Microsoft. See GPG Chapter II.C.2.j for additional guidance on mentoring and data management plan requirements for collaborative proposals. FastLane will combine the proposal. C interview questions and answers for freshers. It is basic c language technical frequently asked interview questions and answers. It includes data structures. Internet Explorer 3. The first. edition of this Ecma Standard was adopted by the Ecma General. Assembly of June 1. The Ecma General Assembly of June 1. In an effort to gain some control over the documentation nightmare that modern medicine has become, this site was created as a repository for. There are several ways to create an array of strings in C. If all the strings are going to be the same length (or at least have the same maximum length), you simply. ECMA- 2. 62 to keep it fully aligned. ISO/IEC 1. 62. 62. Changes between the first and the second edition. The third edition of the. ECMAScript standard was adopted by the Ecma General Assembly of. December 1. 99. 9 and published as ISO/IEC 1. June 2. 00. 2. Significant work was done to. ECMAScript. Although that work was not. The present fifth edition of ECMAScript (published. ECMA- 2. 62 5th. edition) codifies de facto interpretations of the language. Such features include accessor. JSON object encoding format, and a strict. Significant technical enhancement will continue with. Scope #. If the adopted. ISO/IEC 1. 06. 46- 1 subset is not otherwise specified, it is presumed to. BMP subset, collection 3. If the adopted encoding form is. UTF- 1. 6 encoding form. In particular, a conforming. ECMAScript is permitted to provide properties not. In particular, a conforming implementation of. ECMAScript is permitted to support program syntax that makes use of. For dated references, only the edition cited. For undated references, the latest edition of the. ECMAScript as defined here is not intended to be. Instead, it is expected that the computational environment. This is a reference manual for the C programming language as implemented by the GNU Compiler Collection (GCC). Specifically, this manual aims to document. Node:The compiler, Next:Errors, Previous:Basic ideas, Up:Introduction The Compiler. A C program is made by running a compiler which takes the typed source program and. How to declare and access a variable with global scope. America's national educational facility with 18 museums, 9 research centers and 120 affiliates around the world. ECMAScript program will provide not only the objects and other. ECMAScript. program. In such systems, useful functionality is already. In. this way, the existing system is said to provide a host environment. A scripting language is intended for use by both. ECMAScript can provide core scripting capabilities for. Addison Wesley Publishing Co., 1. Self: The Power of Simplicity. OOPSLA. '8. 7 Conference Proceedings, pp. IEEE Std 1. 17. 8- 1. Web Scripting #. Further, the host environment provides a. Scripting code appears within the. HTML and the displayed page is a combination of user interface. The scripting code. By using browser- side. Web- based application. This overview is not part of the. An ECMAScript object is a collection of. Properties are containers that hold other objects. A. primitive value is a member of one of the following built- in types. Object; and a function is a. A function that. is associated with an object via a property is a method. These built- in objects. Object object, the Function object, the Array object, the String object, the. Boolean object, the Number object, the Math object, the Date object, the Reg. Exp object, the JSON object, and the Error objects Error, Eval. Error, Range. Error. Reference. Error, Syntax. Error, Type. Error and URIError. ECMAScript. operators include various. ECMAScript syntax. For example, a variable is not required to have its type. Objects #. Each constructor is. Objects are created by using. Date(2. 00. 9,1. 1) creates a new Date object. Invoking. a constructor without using new has consequences that depend. For example, Date(). Furthermore, a prototype may have a non- null implicit. When a reference is made to a property in an object, that. In other. words, first the object mentioned directly is examined for such a. Figure 1 . In ECMAScript, the state and. Figure 1. illustrates this: CF. Five objects have been. The dashed lines. The property named CFP1. CFp is shared by cf. CF), as are any. properties found in CFp. That is, constructors are. In the above diagram, one could. CFp. 4. 2. 2 The Strict Variant of ECMAScript #. They might do so in the interests of. The strict variant of the language excludes some. ECMAScript. language and modifies the detailed semantics of some features. The. strict variant also specifies additional error conditions that must. Strict mode selection and use of the. ECMAScript is explicitly made at. ECMAScript code units. Because strict mode. In this case, strict mode. In addition, an implementation must support the. Definitions #. The prototype may be the null value. Alternatively, a. Object. create. built- in function. Some native. objects are built- in; others may be constructed during the course of. ECMAScript program. Every. built- in object is a native object. A built- in constructoris a built- in object that is also a constructor. The resulting. object has an internal property whose value is the Boolean value. A. Boolean object can be coerced to a Boolean value. String value#. Each integer value in. UTF- 1. 6 text. The resulting. String value. A. String object can be coerced to a String value by calling the String. Number value#. The resulting. Number value. A. Number object can be coerced to a Number value by calling the Number. Infinity#. An. implementation may provide implementation- dependent built- in. This. grammar has as its terminal symbols characters (Unicode code units). Source. Character. Clause 6. It defines a set of productions, starting from. Input. Element. Div. Input. Element. Reg. Exp. that describe how sequences of such characters are translated into a. These tokens are the reserved words. ECMAScript language. Simple white space. A. Multi. Line. Comment. This grammar. also has as its terminal symbols the characters as defined by. Source. Character. The lexical and. Reg. Exp grammars share some productions. The Numeric String Grammar #. This. grammar is similar to the part of the lexical grammar having to do. Source. Character. This grammar has ECMAScript tokens defined by the lexical. It defines a set of. Program. that describe how sequences of tokens can form syntactically correct. ECMAScript programs. The. program is syntactically in error if the tokens in the stream of. Program. with no tokens left over. Certain additional token. The JSON grammar is given in. The JSON lexical grammar is used to translate. ECMAScript lexical grammar. The JSON syntactic grammar describes how. JSON lexical grammar can form. JSON object descriptions. The JSON lexical grammar. ECMAScript lexical grammar. The JSON. syntactic grammar is similar to parts of the ECMAScript syntactic. Productions of the JSON syntactic grammar are distinguished. These are to appear in a program exactly as. All terminal symbol characters specified in this way are to. Unicode character from the ASCII. Unicode ranges. The definition of a nonterminal is introduced by the name of. For example, the syntactic definition: While. Statement : while(Expression )Statement. While. Statement. Expression. followed by a right parenthesis token, followed by a Statement. As another example, the syntactic. Argument. List: Assignment. Expression. Argument. List. ,Assignment. Expression. that an Argument. List. may represent either a single Assignment. Expression. or an Argument. List. followed by a comma, followed by an Assignment. Expression. The result. Argument. List. may contain any positive number of arguments, separated by commas. Assignment. Expression. The. alternative containing the optional symbol actually specifies two. This means that: Variable. Declaration: Identifier. Initialiseropt. convenient abbreviation for: Variable. Declaration: Identifier. Identifier. that: Iteration. Statement: for. (Expression. No. Inopt. ; Expressionopt. Expressionopt. convenient abbreviation for: Iteration. Statement: for. ( ; Expressionopt. Expressionopt. (Expression. No. In. ; Expressionopt. Expressionopt. in turn is an abbreviation for: Iteration. Statement: for. ( ; ; Expressionopt. Expressionopt). (Expression. No. In. ; ; Expressionopt). Expression. No. In. Expressionopt). in turn is an abbreviation for: Iteration. Statement: for. ( ; ; )Statementfor. Expression. ; )Statementfor. Expression. No. In . Statementfor. (Expression. No. In . (Expression. No. In . ; )Statementfor. Expression. No. In . Iteration. Statement. For. convenience, the set can also be written as a nonterminal, in which. For example, given the definitions. Decimal. Digit : :one. Decimal. Digits: :Decimal. Digit. Decimal. Digits. Lookahead. Example: :n. For example. the production: Return. Statement: return. For example. the lexical grammar for ECMAScript contains the production: Non. Zero. Digit : :one. Non. Zero. Digit : :1. For example, the. Identifier: :Identifier. Name but. not Reserved. Word. that the nonterminal Identifier. Identifier. Name. Reserved. Word. These algorithms are used to precisely specify the. ECMAScript language constructs. The algorithms. are not intended to imply the use of any specific implementation. In practice, there may be more efficient algorithms. The notation Result(n). Substeps are indented and may themselves be. For example. Substep. If a step or substep begins with. Algorithms in this standard that model. If a. mathematical operation or function is applied to a floating- point. The calling. algorithms are also terminated, until an algorithm step is reached. Once such an algorithm step has. Source Text #. The text is. Unicode Normalised Form C. Unicode Technical Report. Conforming ECMAScript implementations are not required to. Such a source text may include. UTF- 1. 6 character. If an actual source text is encoded in a form other than. UTF- 1. 6. Source. Character : . Unicode code unit. Within a comment, such an escape. Within a. string literal or regular expression literal, the Unicode escape. In a Java program, if the Unicode escape. A. for example, occurs within a single- line comment, it is interpreted. Unicode character 0. A. is line feed) and therefore the next character is not part of the. Similarly, if the Unicode escape sequence \u. A. occurs within a string literal in a Java program, it is likewise. RAID - Wikipedia, the free encyclopedia. RAID (originally redundant array of inexpensive disks, now commonly redundant array of independent disks) is a data storage virtualization technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both. The different schemas, or data distribution layouts, are named by the word RAID followed by a number, for example RAID 0 or RAID 1. Each schema, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives. History. Gibson, and Randy Katz at the University of California, Berkeley in 1. In their June 1. 98. Although failures would rise in proportion to the number of drives, by configuring for redundancy, the reliability of an array could far exceed that of any large single drive. Most use simple XOR, but RAID 6 uses two separate parities based respectively on addition and multiplication in a particular Galois field or Reed. For example, a fast SSD can be mirrored with a mechanical drive. For this configuration to provide a significant speed advantage an appropriate controller is needed that uses the fast SSD for all read operations. These are called levels. Originally, there were five RAID levels, but many variations have evolved, notably several nested levels and many non- standard levels (mostly proprietary). RAID levels and their associated data formats are standardized by the Storage Networking Industry Association (SNIA) in the Common RAID Disk Drive Format (DDF) standard. The capacity of a RAID 0 volume is the sum of the capacities of the disks in the set, the same as with a spanned volume. There is no added redundancy for handling disk failures, just as with a spanned volume. Thus, failure of one disk causes the loss of the entire RAID 0 volume, with reduced possibilities of data recovery when compared to a broken spanned volume. Striping distributes the contents of files roughly equally among all disks in the set, which makes concurrent read or write operations on the multiple disks almost inevitable and results in performance improvements. The concurrent operations make the throughput of most read and write operations equal to the throughput of one disk multiplied by the number of disks. Increased throughput is the big benefit of RAID 0 versus spanned volume. Data is written identically to two (or more) drives, thereby producing a . Thus, any read request can be serviced by any drive in the set. If a request is broadcast to every drive in the set, it can be serviced by the drive that accesses the data first (depending on its seek time and rotational latency), improving performance. Sustained read throughput, if the controller or software is optimized for it, approaches the sum of throughputs of every drive in the set, just as for RAID 0. Actual read throughput of most RAID 1 implementations is slower than the fastest drive. Write throughput is always slower because every drive must be updated, and the slowest drive limits the write performance. The array continues to operate as long as at least one drive is functioning. All disk spindle rotation is synchronized and data is striped such that each sequential bit is on a different drive. Hamming- code parity is calculated across corresponding bits and stored on at least one parity drive. All disk spindle rotation is synchronized and data is striped such that each sequential byte is on a different drive. Parity is calculated across corresponding bytes and stored on a dedicated parity drive. This level was previously used by Net. App, but has now been largely replaced by a proprietary implementation of RAID 4 with two parity disks, called RAID- DP. As a result, more I/O operations can be executed in parallel, improving the performance of small transfers. Unlike RAID 4, parity information is distributed among the drives, requiring all drives but one to be present to operate. Upon failure of a single drive, subsequent reads can be calculated from the distributed parity such that no data is lost. RAID 5 requires at least three disks. Double parity provides fault tolerance up to two failed drives. This makes larger RAID groups more practical, especially for high- availability systems, as large- capacity drives take longer to restore. RAID 6 requires a minimum of four disks. As with RAID 5, a single drive failure results in reduced performance of the entire array until the failed drive has been replaced. The larger the drive capacities and the larger the array size, the more important it becomes to choose RAID 6 instead of RAID 5. The elements of a RAID may be either individual drives or arrays themselves. Arrays are rarely nested more than one level deep. When the top array is RAID 0 (such as in RAID 1+0 and RAID 5+0), most vendors omit the . If a single drive failure occurs then one of the stripes has failed, at this point you are running effectively as RAID 0 with no redundancy, significantly higher risk is introduced during a rebuild than RAID 1+0 as all the data from all the drives in the remaining stripe has to be read rather than just from 1 drive increasing the chance of an unrecoverable read error (URE) and significantly extending the rebuild window. The array can sustain multiple drive losses so long as no mirror loses all its drives. Such configurations include the following: Linux MD RAID 1. RAID driver that in its . Regular RAID 1, as provided by Linux software RAID, does not stripe reads, but can perform reads in parallel. A software solution may be part of the operating system, part of the firmware and drivers supplied with a standard drive controller (so- called . Software RAID can be implemented as: A layer that abstracts multiple devices, thereby providing a single virtual device (e. Linux kernel's md and Open. BSD's softraid)A more generic logical volume manager (provided with most server- class operating systems, e. Veritas or LVM)A component of the file system (e. ZFS, GPFS or Btrfs)A layer that sits above any file system and provides parity protection to user data (e. As it always stripes over top- level vdevs, it supports equivalents of the 1+0, 5+0, and 6+0 nested RAID levels (as well as striped triple- parity sets) but not other nested combinations. ZFS is the native file system on Solaris and illumos, and is also available on Free. BSD and Linux. Open- source ZFS implementations are actively developed under the Open. ZFS umbrella project. A particularity is the dynamic rebuilding priority which runs with low impact in the background until a data chunk hits n+0 redundancy, in which case this chunk is quickly rebuilt to at least n+1. On top, GPFS supports metro- distance RAID 1. Some of the Microsoft desktop operating systems support RAID. For example, Windows XP Professional supports RAID level 0, in addition to spanning multiple drives, but only if using dynamic disks and volumes. Windows XP can be modified to support RAID 0, 1, and 5. For instance, consider a computer whose disk is configured as RAID 1 (mirrored drives); if the first drive in the array fails, then a first- stage boot loader might not be sophisticated enough to attempt loading the second- stage boot loader from the second drive as a fallback. The second- stage boot loader for Free. BSD is capable of loading a kernel from such an array. However, hardware RAID controllers are expensive and proprietary. To fill this gap, inexpensive . During early bootup, the RAID is implemented by the firmware and, once the operating system has been more completely loaded, the drivers take over control. Consequently, such controllers may not work when driver support is not available for the host operating system. An advantage of this model over the pure software RAID is that. This detects bad blocks before use. Consequently, using RAID for consumer- marketed drives can be risky, and so- called . A utility called WDTLER. The utility enabled TLER (time limited error recovery), which limits the error recovery time to seven seconds. Around September 2. Western Digital disabled this feature in their desktop drives (e. Similar technologies are used by Seagate, Samsung, and Hitachi. Of course, for non- RAID usage, an enterprise class drive with a short error recovery timeout that cannot be changed is therefore less suitable than a desktop drive. Many studies cite operator fault as the most common source of malfunction. An array is also vulnerable to controller failure because it is not always possible to migrate it to a new, different controller without data loss. Since many drive failures are due to mechanical issues (which are more likely on older drives), this violates the assumptions of independent, identical rate of failure amongst drives; failures are in fact statistically correlated. In a study of about 1. The probability of two failures in the same 1. The associated media assessment measure, unrecoverable bit error (UBE) rate, is typically guaranteed to be less than one bit in 1. SCSI, FC, SAS or SATA), and less than one bit in 1. IDE/ATA/PATA or SATA). Rebuilding a RAID set after a drive failure fails if such an error occurs on one or more of the remaining drives, and increasing drive capacities and large RAID 5 instances have led to the maximum error rates being insufficient to guarantee a successful recovery. Thus, an URE during a RAID 5 rebuild typically leads to a complete rebuild failure. The recovery of UREs involves remapping of affected underlying disk sectors, utilizing the drive's sector remapping pool; in case of UREs detected during background scrubbing, data redundancy provided by a fully operational RAID set allows the missing data to be reconstructed and rewritten to a remapped sector. Therefore, larger- capacity drives may take hours if not days to rebuild, during which time other drives may fail.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2016
Categories |