Conventional memory is the first 640kb of your system memory. Typically, this is where DOS and DOS applications ran from. Another section of your system memory is the Upper Memory. The upper memory, is the 384kb after the conventional memory. After the upper memory, is the extended memory. The first 64kb of the extended memory is called the High Memory. Maybe it might be best to find an article about this but basically, as programs got bigger and bigger, MS made some changes to DOS and had DOS load itself in the high memory area instead of the conventional memory in order to free up space. XP doesn't rely on DOS in order to boot as Windows 3.1, 95 and 98 did. This is why you really don't use these terms that often anymore.
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