雲端運算的五四三，關於雲端運算的定義

近年來關於雲端運算，不斷有各種討論及應用出現，甚至李家同教授也提出所謂"雲端"就是以後大家都會去的地方，呵，這個定義是滿好笑的。不過李家同教授是平行演算的行家，這肯定是開玩笑的，不必當真了。

簡單地說，雲端可以拆成 雲 跟 端 兩個部份
來解讀，
雲 當然是遠處摸不到的那個服務，端其實便是client（使用者這一端），由這樣的角度來看雲端便有一種Web service的感受出現了，其實Web servie本身也正是雲端運算下的一種商業服務。未來3C產業也會在這兩端去發展，舉凡手機，PDA,筆電 因為是使用者端所必備的工具，硬體商便要提供更輕便的上網工具給使用者；而深處另一端-雲，像 Google ，Yahoo，Amazon 等服務商 便要研究如何將軟體及硬體的結合上，以至於提供用戶端更快速便利的服務，由此來看雲端可謂無處不在。

這邊美國 NIST 有一篇文章雲端運算的定義一文很值得一讀，他們將Cloud computing 定義分成五四三的口訣，
我認為這五四三正代表了雲端運算 如何由構成 經 佈建，最終至 運用 三大階段及領域。

構成：五種必備特徵 
(On-demand self-service, Broad network access, Resource pooling, Rapid elasticity, Measured Service)
建置：四種部署型態 Public,Private,Community,Hybrid cloud,
功能：提供三種類型的服務  (Cloud Software as a Service (SaaS), Cloud Platform as a Service (PaaS), Cloud Infrastructure as a Service (IaaS))

看完這篇文章 相信對於雲端運算的涵蓋及定義不只是"升天"一說了！（偷笑）
原文如下：

NIST Cloud Computing Program

Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics (On-demand self-service, Broad network access, Resource pooling, Rapid elasticity, Measured Service); three service models (Cloud Software as a Service (SaaS), Cloud Platform as a Service (PaaS), Cloud Infrastructure as a Service (IaaS)); and, four deployment models (Private cloud, Community cloud, Public cloud, Hybrid cloud). Key enabling technologies include: (1) fast wide-area networks, (2) powerful, inexpensive server computers, and (3) high-performance virtualization for commodity hardware.
The Cloud Computing model offers the promise of massive cost savings combined with increased IT agility. It is considered critical that government and industry begin adoption of this technology in response to difficult economic constraints. However, cloud computing technology challenges many traditional approaches to datacenter and enterprise application design and management. Cloud computing is currently being used; however, security, interoperability, and portability are cited as major barriers to broader adoption.
The long term goal is to provide thought leadership and guidance around the cloud computing paradigm to catalyze its use within industry and government. NIST aims to shorten the adoption cycle, which will enable near-term cost savings and increased ability to quickly create and deploy enterprise applications. NIST aims to foster cloud computing systems and practices that support interoperability, portability, and security requirements that are appropriate and achievable for important usage scenarios.
http://www.nist.gov/itl/cloud/index.cfm

雲端計算另一定義， 李家同有趣的的"升天說" (看樣子古人Ancient古早就懂得雲端了)