The Multi-Boot Configuration Handbook

Preparing Disk Space

After you've trimmed any fat from your existing OS, you'll be in a much better position to judge how much space to devote to your old OS and your new one. You can use space requirements as specified by the OS's producer, combined with those for any major applications you want to install, as a starting point in estimating how much space you need. Keep in mind, however, that these space requirements are often extremely optimistic. For a more realistic assessment, consider how much space you use in your current OS, compared to how much space that OS claims it needs. If your current OS claims to need 200MB but it actually consumes 2GB (including applications and data files), a similar tenfold-size adjustment might be in order ...