Is an ATA133 HDD ok on ATA33 system?

[Sylvander]

With regard to this thread (http://www.pcguide.com/vb/showthread.php?t=35109).

Would it be ok to fit the [80GB version of the] "Hitachi Deskstar 7K80" (manufacturers part number 13G0310)?
See it here at ebuyer (http://www.ebuyer.com/customer/products/index.html?rb=5410794779&action=c2hvd3N1YmNhdGVnb3J5X3NlYXJjaA==&cat_uid=4&stid=2), where they say it's ATA100 yet here at Hitachi (http://www.hitachigst.com/portal/site/hgst/?epi_menuItemID=984274a23736408aa5a8f2b6aac4f0a0&epi_menuID=8d237906f078b6fd25ad4e8060e4f0a0&epi_baseMenuID=22f0deefa8f3967dafa0466460e4f0a0) they say it's "ATA Ultra 133 (Parallel)" [whatever is the significance of "Parallel"?]
So which is it, any idea?

Is ATA 100 or 133 backward compatible with an ATA 33 system?
Would I need to use an 80 wire signal cable, or would 40 wire be ok?

[Sylvander]

Found this (http://www.pcguide.com/ref/hdd/if/ide/unstd_Ultra.htm) [click on "Making Sense of IDE/ATA"] here at the PC-Guide.
Notice it says:
"The folks who create the IDE/ATA standards always ensure backwards compatibility. This means that a drive corresponding to a newer standard will still work on an IDE channel in an older PC. Similarly, older drives will work on newer systems, in most cases. When older and newer hardware are mixed, the newer hardware will just run at whatever the maximum speed is of the older hardware."

[Sylvander]

Found this (http://www.pcguide.com/ref/hdd/if/ide/modes_UDMA.htm) on the topic of 80 versus 40 conductor ribbon cables and Ultra ATA modes.

Notice where it says:
"For Ultra DMA modes over 2, an 80-conductor cable must be used. If an 80-conductor cable is not detected by the system, 66 MB/s or 100 MB/s operation will be disabled.

On new systems there are few issues with running Ultra DMA, because the hardware is all new and designed to run in Ultra DMA mode. With older systems, things are a bit more complex. In theory, new drives should be backwards compatible with older controllers, and putting an Ultra DMA drive on an older PC should cause it to automatically run in a slower mode, such as PIO mode 4. Unfortunately, certain motherboards don't function well when an Ultra DMA drive is connected, and this may result in lockups or errors. A BIOS upgrade from the motherboard manufacturer is a good idea, if you are able to do this. Otherwise, you may need to use a special Ultra DMA software utility (available from the drive manufacturer) to tell the hard disk not to try to run in Ultra DMA mode. The same utility can be used to enable Ultra DMA mode on a drive that is set not to use it. You should use the utility specific to whatever make of drive you have."