Simply put what is the difference between the two 1. Ultra ATA-66/100/133 2. UDMA-66/100/133 IDE

Nothing. They are the same thing. UDMA Ultra Direct Memeory Access ATA Advanced Technology Attachment (the general term for the modern day IDE harddrive. All modern IDE hard drives are ATA (excluding SCSI and the new Serial drives). IDE Intelligent Drive Electronics or Integrated Drive Electronics one or the other! The 33, 66, 100, 133 refers to the speed the hard drive can communicate at. Your board needs to support the relevant 33, 66, 100, or 133 for it to talk at that speed. If you put an ATA133 on an ATA100 board, it will theoretically talk at ATA100 speed as that is the fastest the board supports.

Francis up there ^ did a very swell job of explaining, but I also wanted to ad the fact that you can install a ide to pci adapter card that can some times surpass the boards speeds :-)

Don't forget that you have to use the 80 wire/40 pin ide cable to have the drives work at the high speeds. Charles

They are the same. This started when IDE went to EIDE which was 16. Eide became UDMA 33 and later 66. Well Seagate and some others made the Eide switch but called it ATA. I have always wondered something: If the connector is to 40 pins how can an 80 wire cable make any difference? This is as confusing as the laptop battery Ray couldn't understand.

having two wires for each pin does something to the magnetic field of the cable making data pass throught it quicker, this works for the same reason cat 5 networking cable is made up of twisted pairs of wires.