The hard disk space depends on the size of the RAM memory module installed. The size of the virtual memory paging file pagefile.sys is determined by the size of the installed memory at the time of restoring the computer. The default value of the virtual memory paging file is set to 1.5 times larger than the computer's RAM capacity.
If the computer is equipped with memory larger in size, the memory located for the virtual memory paging file also increases in size. Thus, the available free space in the hard disk drive becomes smaller. This symptom also occurs when RAM is added to the computer right after purchase.
To avoid this symptom, always reserve a larger hard disk space for the installation of the operating system.
For more details, please refer to the following solution in Microsoft's technical support website.
Article ID: Q308417
Last Reviewed: October 18, 2001
Title: [HOW TO] Set Performance Options