How many hard disk supported by intel pentium 4

You can chain 255 on a scsi chain, you can get sas controllers with support for 128 drives. You can hang a bunch of usb devices off of one port with a hub.

So the answer is practically unlimited. Your processor isn't what limits the number of drives, it is the OS and the motherboard.
 
If you are running a Pentium 4 then most likely you are also running IDE and PATA ribbion / master/slave/cs pinned hard drives. Those have a limit of 4 drives. Even the CD ROm is included.

As others have said USB and SCSI will add however many drives you wish.

I cannot elaborate anymore without knowing what Motherboard and OS you are running.