ASCII如何解释文本文件字节数？同内容文本文件大小不同的原因是什么？

Great questions! Let's break them down one by one:

ASCII is a character encoding standard where every single character—including printable ones like letters, numbers, and symbols, plus non-printable control characters like newlines, tabs, or carriage returns—is represented by exactly 1 byte.

This strict 1:1 mapping between characters and bytes makes it trivial to connect a plain ASCII text file's content to its byte size. For example:

• If your file has the text "Hello World" with no line breaks, that's 11 characters → 11 bytes.
• If you add a newline at the end, that's 12 total characters (11 visible + 1 invisible newline) → 12 bytes.

No fancy calculations needed—just count all characters (even the invisible ones that handle formatting) and you've got your file's byte count.

First off: creation time has absolutely nothing to do with a file's size. File size is determined by the actual data stored in the file, not metadata like creation timestamp, author, or file permissions.

The real reasons for size differences between "identical" text files almost always fall into these categories:

• Line ending inconsistencies: Windows uses a two-byte sequence (\r\n, carriage return + newline) to mark line breaks, while Unix/Linux/macOS uses a single-byte newline (\n). If your text has 5 lines, the Windows version will be 5 bytes larger than the Unix one—even though the visible content looks exactly the same.
• Character encoding mismatches: If one file is saved as ASCII (1 byte per character) and the other as UTF-16 (2 bytes per character) or UTF-32 (4 bytes per character), the size will jump dramatically. Even UTF-8 can cause differences: some editors add a 3-byte UTF-8 BOM (byte order marker) at the start of the file, while others don't—adding 3 extra bytes without changing the visible text.
• Hidden extra characters: It's common for editors to add invisible characters without you noticing: trailing spaces at the end of lines, extra blank lines at the end of the file, or special control characters from copy-pasting between different systems. These add bytes to the file even though the visible content seems identical.
• File system edge cases (rare): In some cases, the disk space occupied (not the logical file size) might differ due to how the file system allocates storage clusters. But this is a storage layer detail, not a difference in the actual data stored in the file.

内容的提问来源于stack exchange，提问作者Steven Chen