这个程序占用2.5 兆字节的磁盘空间，可以在标准个人电脑上运行。
The program takes up 2.5 megabytes of disk space and can be run on a standard personal computer.
但如果字符串是一个地址或可选的字段，那么磁盘上可能会有成兆字节的零。
But if the string is an address or optional field, you may have megabytes of zeroes on disk.
若必须处理许多兆字节的XML文档，花费内存、磁盘空间和CPU开销来操作这么大的文档通常是不实际的。
If you must deal with many-megabyte XML documents, it's often impractical to spend the memory, disk space, and CPU overhead to manipulate such huge documents.
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