Cloud computingクラウドコンピューティング is a way of using IT resources such as servers and software that are set up across the network (usually in a provider's facilities), drawing on them only when you need them and only as much as you need.
On-premises
Renting a provider's cloud
Owner of the equipment
Your company
Service provider
Cost to get started
Equipment must be bought and installed first
You can start without buying equipment
How charges work
Costs of owned equipment keep running
Pay by amount or period of use
Changing capacity
Add or remove equipment
Change the contract or settings
Charges are usually based on how much or how long you use the service, which makes it easier to keep the up-front cost of buying equipment low. Offerings are grouped by how many layers the provider supplies, and each such type is called a service modelサービスモデル. A setup where a company places its information systems in facilities it owns and manages, and runs them itself, is called on-premisesオンプレミス.
AnalogyIt is like hooking up to the water mains instead of digging your own well, then paying for however much comes out of the tap.
How to rememberNetwork diagrams have long drawn the internet side as a cloud shape, so "cloud" became the name for using resources without caring where they actually sit.
Exam points
ExamCloud computingクラウドコンピューティング names a model for providing and using resources, in which a provider prepares computer resources and lets users work with them.
ExamUsers reach the resources over the network without caring where they are located, obtain them at the moment they are needed, and can scale the amount up or down later.
Mix-upOn-premisesオンプレミス means keeping information systems in your own facilities and running them yourself; what separates it from renting a provider's resources is who owns the equipment.
SaaS (Software as a Service) is a model in which users rent, over the network, the functions of application softwareアプリケーションソフトウェア running on a provider's servers.
The provider takes care of installing and updating the software and managing the servers it runs on, so users only need to call up its functions from a browser or similar. Many client companies share the same software, and each pays according to how much or how long it uses it.
AnalogyIt is like subscribing to a streaming service instead of buying a shelf of movie discs, and playing whatever you want whenever you want.
How to rememberThe leading S stands for Software. Since the product is the software itself, the only job left for the user is to use it.
Exam points
ExamSaaS is the service model in which the provider supplies everything up to the application layer, so users neither develop nor install the business software themselves.
PaaS (Platform as a Service) is a model in which a provider offers, over the network, the platform基盤 for building and running applications.
The platform includes the OS and middlewareミドルウェア, software such as a database management system that works between the OS and applications, and the provider also supplies the servers they run on. Users build and run their own applications on top, leaving maintenance and updates of the platform to the provider.
AnalogyIt is like renting a kitchen already fitted with cookware and a stove, then cooking from your own recipes.
How to rememberP stands for Platform, the same word as a railway platform. The railway company builds the platform, while the trains that leave from it (the apps) are the user's own.
Exam points
Mix-upSaaS lets you use a finished application as it is, while PaaS rents the platform on which you place your own applications. The two differ in whether the provider or the user supplies the application.
IaaS (Infrastructure as a Service) is a model in which a provider offers, over the network, hardware resourcesハードウェア資源 such as server processing power, storage and network lines.
Layer
IaaS
PaaS
SaaS
Application
User
User
Provider
OS and middleware
User
Provider
Provider
Servers, storage, lines
Provider
Provider
Provider
Users choose and rent the number of machines and the capacity they need, then install and manage the software from the OS up on their own. They are free to decide the configuration, but in exchange more of the operating work stays on their side.
AnalogyIt is like renting a building where only the frame and walls are finished, and fitting out the interior and furniture yourself.
How to rememberI stands for Infrastructure, the things like roads and water mains that hold everything up from below. It points to the bottom layer of the service models.
Exam points
Mix-upWith PaaS the provider supplies everything up to the OS and middleware, while with IaaS it supplies only the hardware resources and the user sets up everything from the OS up.
DaaS (Desktop as a Service) is a model that runs a PC's desktop environmentデスクトップ環境, including the OS, applications and data, on a cloud server and delivers it over the network to the user's device.
Processing and data storage happen on the server, while the device shows the screen and sends keyboard and mouse input to the server. Because no data needs to stay on the device, losing it is less likely to leak information, and the same environment can be called up from another device.
AnalogyIt is like leaving your study in a distant building and, wherever you are, working at its desk through a window.
How to rememberD stands for Desktop. What arrives is not a single app but everything on top of the desk.
Key points
With cloud computingクラウドコンピューティング, you use IT resources over the network; when you rent them from a provider you need not own the equipment, and you can change the amount you use later.
Service models differ in how many layers the provider supplies, and the less the provider supplies, the more the user has to manage.
DaaS lets you use a desktop environment without keeping data on the device, which helps prevent information leaks when a device is lost.