An OS (Operating System) is the basic software (基本ソフトウェア) that manages the hardware and provides common functions to applications.
Users
Application software (apps)
OS (basic software)
Hardware
An application only has to ask the OS to draw the screen or read and write storage, so it does not need its own control logic for each device. Multitasking (マルチタスク), where several programs run side by side, also works because the OS divides up processor time. Right after a PC is switched on, a separate program called BIOS runs to set up the hardware before the OS takes over.
AnalogyIt is a bit like a railway company. It looks after all the tracks and signals, so passengers (apps) just pick a destination, get on, and arrive.
How to rememberTo operate a machine is to run it. The system whose job is running the machine is the Operating System.
Exam points
ExamThe OS hands out resources such as the processor and main memory (主記憶) to each running program.
ExamMultitasking (マルチタスク) is an OS function that slices processor time finely and passes it to several tasks in turn, so they appear to run at once.
ExamWhen a PC is powered on, BIOS runs before the OS, and only then is the OS loaded.
Virtual memory (仮想記憶) is an OS mechanism that uses part of auxiliary storage as an extension of main memory, making it look as if there is more memory than is physically installed.
A program too big for main memory
Move unused parts to auxiliary storage
Bring needed parts back to main memory
A program larger than main memory runs
By repeating this moving out and back in, programs larger than main memory can run.
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The OS moves the parts that do not fit in main memory out to auxiliary storage and brings them back when their turn comes. This swapping lets programs run without being bound by the physical size of main memory, though main memory itself does not grow. When swapping becomes so frequent that processing slows to a crawl, the state is called thrashing (スラッシング).
AnalogyThink of backstage and the stage. Only so many actors fit on stage, but when actors whose scene is over step back and the next ones come on, a play with a large cast can go ahead. With too many changeovers, though, the play stalls.
How to rememberVirtual means "in effect". It is not real main memory, but in effect it works as memory, hence virtual memory.
Exam points
ExamThe aim of virtual memory (仮想記憶) is to let programs larger than the physical capacity of main memory run.
ExamThrashing (スラッシング) comes from a shortage of main memory (主記憶), so adding main memory removes it.
ExamOne way to choose which part to push out of main memory is the LRU method, which picks the part that has gone unused the longest.
User management (ユーザー管理) is the OS function that registers an account (アカウント) for each user and checks at login whether the person is really that user (authentication, 認証).
Register an account
Check ID and password at login
Work as an identified user
Once confirmed, the OS treats the operations as that user's.
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Even when several people share one computer, separate accounts let the OS tell who is operating it. Users can also be gathered into groups (グループ), such as by department, and handled together. A user identified in this way is the "who" in the access rights covered later.
AnalogyIt works like the front desk of a members-only gym. You register as a member when you join, and on each visit your membership card is checked to confirm it is you.
How to rememberThe login screen is the front door of user management.
Exam points
Mix-upAuthentication in user management (ユーザー管理) is the step that confirms who the person is; what they may do is decided by the access rights (アクセス権) settings.
File management (ファイル管理) is the OS function that handles data in named units called files (ファイル) and organizes them in a hierarchy of folders (フォルダ, also called directories).
Top-level folder
Documents folder
Meeting minutes file
Schedule file
Photos folder
Trip folder
Image file
Users can open or save a file just by giving its name, without knowing where on the storage device the data physically sits. Because folders can hold further folders, files can be sorted into a hierarchy that branches like a tree.
AnalogyIt resembles the classified shelves of a library. Narrow down from the subject shelf to a smaller section within it, and you reach the book you are after.
How to rememberIn a path, "/" or "\" (shown as "¥" on Japanese systems) is the separator for stepping down one folder level.
Access rights (アクセス権) are settings that define which users may perform which operations, such as read (読取り) and write (書込み), on a file or folder.
Users of the sales summary file
Read
Write
Accounting staff
Yes
Yes
Sales staff
Yes
No
Guest account
No
No
Kinds of operations include read, which views the content, write, which changes it, and execute (実行), which runs it as a program. Permissions can be granted per user or per group, and the basic idea is to give only what the job requires (least privilege, 最小権限).
AnalogyIt is like the different keys in an apartment building. A resident's key opens both their own unit and the shared areas, while the code given to couriers opens only the parcel lockers.
How to rememberR, W and X stand for Read, Write and eXecute: viewing, changing and running.
Exam points
ExamTo make a new file by copying an existing one, the person copying must have permission to read the original.
ExamOpening a file to read it requires read permission (読取り権限), and saving changes over it requires write permission (書込み権限) for that file.