What system? The practical maximum depends mainly on the motherboard and OS.
E.g., some motherboards cannot detect a HDD larger than 32GB, and the RAM limit may be 256MB or 1GB per slot. Windows XP cannot use more than 127GB HDD without a Service Pack.
If you're talking about your own motherboard, read the manual.
Hi Guest we just wanted to alert you to a major change in the forum. We will no longer be allowing the posting of outgoing links. Please use the attachment feature to attach media to your posts.