The root directory (ルートディレクトリ) is the directory at the top of a hierarchical directory structure (階層型ディレクトリ構造), which organizes files in the shape of a tree.
Root
home
taro
memo.txt
work
data.csv
A directory is a container for files and lower-level directories, and since a directory can hold further directories, the whole structure forms an upside-down tree. Showing a location by writing the route from the root down to the target file is called an absolute path (絶対パス); because its starting point never moves, the notation stays the same wherever you are working.
AnalogyIf you write an address in full, from the region down to the house number, a letter reaches the same house no matter where it is posted from. An absolute path, written from the root, works the same way.
How to rememberA "root" is where a tree begins. Draw the tree upside down and the root ends up at the top.
Exam points
ExamAn absolute path (絶対パス) is written from the root, so the same location always has the same notation, wherever the current directory (カレントディレクトリ) happens to be.
ExamA location is fixed by the whole path, so directories with the same name can exist side by side as long as their parent directories (親ディレクトリ) differ.
The current directory (カレントディレクトリ) is the directory a user or program is working from right now, and it changes when you move to another directory.
Current: 2026
Parent: photo
One more up: home
b.mp3 in music
Go into music under home and arrive at b.mp3.
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Writing the route from the current directory to the target is called a relative path (相対パス). In most systems, "." stands for the directory you are in and ".." for its parent, one level up. Even for the same file, the relative path may have to be written differently once the current directory changes.
AnalogyDirections such as "go back two corners from here, then turn right" only make sense from where the speaker is standing.
How to remember"Current" means "present", as in current events: the news that is happening now.
Exam points
ExamIn a relative path (相対パス), each ".." moves up one level, and from there you follow the lower-level directory names in order to reach the target.
ExamRewriting the location a relative path points to as a route traced down from the root gives the absolute path (絶対パス).
Mix-upThe current directory (カレントディレクトリ) moves as you work, while the root directory (ルートディレクトリ) stays fixed at the top of the hierarchy.
A file extension (ファイル拡張子) is the string after the last period in a file name that shows the file's type or format.
Example extension
File type
.txt
Plain text only
.png
Image
.mp4
Video
.zip
Files bundled and compressed together
The OS uses the extension to decide which application opens the file and which icon to show. Because the extension is only part of the name, changing it does not convert the format of the data inside. When you search by replacing part of a file name with a symbol that stands in for any characters, that symbol is called a wildcard (ワイルドカード).
AnalogyIt is like writing "Invoice enclosed" on the front of an envelope. Anyone can tell at a glance what is inside, but rewriting those words does not change the document in the envelope.
How to rememberTo "extend" something is to make it longer. Think of the extension as the bit that lengthens the file name at the end.
Exam points
ExamWhen searching by name, the wildcard (ワイルドカード) "?" matches exactly one character and "*" matches a string of zero or more characters, and both work the same way on the extension (拡張子) part.
Fragmentation (フラグメンテーション, also 断片化) is the state in which the data of one file is recorded in separate places spread across a storage device.
Files stored contiguously
Deletions leave gaps
A new file is split into the gaps
Rearranged into contiguous space
Rearranging the data into contiguous areas makes reading faster on a hard disk.
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As files are created and deleted over and over, free space breaks into small pieces, and new data can no longer be written in one continuous stretch. Reading split data means seeking out distant locations one after another, so reads take longer on a hard disk. The process that fixes this by rearranging scattered data into contiguous areas is called defragmentation (デフラグ).
AnalogyWhen a parking lot has only scattered empty spaces, a group arriving in several cars cannot park together, and collecting them later means driving all over the lot.
How to rememberA "fragment" is a broken-off piece. Picture a file shattered into pieces.
Exam points
ExamOn storage devices that read by moving a read position, such as hard disks, leaving fragmentation (断片化) alone slows down reading. Defragmentation (デフラグ) fixes it by rearranging the data into contiguous locations.
An archive (アーカイブ) means bundling several files into one file, or the single file that results.
Once bundled, a large number of files can be handled as a single file when you save, store or hand them over. The ZIP format, for example, can also compress the data while bundling it to make it smaller.
AnalogyWhen you move house, packing small items into a cardboard box lets you carry them as one parcel.
How to remember"Archive" originally meant a place where records are kept. Picture putting all your papers away in one spot.
Exam points
ExamAn archive (アーカイブ) is a way of bundling many files into one so they are easier to save and store.
Mix-upArchiving (アーカイブ) reduces the number of files to one, while compression (圧縮) reduces the amount of data. Many formats do both at once, but they are separate functions.
A backup (バックアップ) is a copy of data kept on a separate medium or in a separate place, in case the data is lost through a failure, a user's mistake or a disaster.
Method
What each run copies
What a restore needs
Full backup
All target data
That full backup
Differential backup
Changes since the last full backup
The full backup plus the differential taken at the point you want to restore to
Incremental backup
Changes since the previous backup
The full backup plus every incremental up to the point you want to restore to
Bringing lost data back from a copy is called a restore (リストア, also 復元). Methods include, for example, a full backup (フルバックアップ) that copies everything, a differential backup (差分バックアップ) that takes the changes since the last full backup, and an incremental backup (増分バックアップ) that takes only the changes since the previous backup.
AnalogyIt is like leaving a spare house key with a relative who lives somewhere else. Even if you lose your key at home, the spare one gets you back in.
How to rememberTo "back up" someone is to support them from behind. The copy stands behind the original data, ready to step in.
Exam points
ExamTo restore under the incremental backup (増分バックアップ) method, you use the base full backup (フルバックアップ) and every incremental backup taken from then up to the point you want to restore to.
ExamTo restore under the differential backup (差分バックアップ) method, the minimum you need is the last full backup (フルバックアップ) and the differential backup taken at the point you want to restore to.