It's not 100 "mhz" but that's besides the point =).
You can tell if your drive is running at ATA100 in several different ways:
* The drive is configured for UDMA 5 (ATA/100) by default. You can make sure of this by looking at the BIOS info page that prints as your computer is booting. If you're using an external mass storage device, it should print UDMA 5 while initializing.
* Only Windows 2000 SP2 supports ATA/100. Windows 2000/SP1 has UDMA support up to ATA/66.
* Intel has an ATA/100 driver for Windows 2000/SP1, but there is no reason not to upgrade to SP2.
* Under your control panel, under Controllers->Properties, there is an "Advanced Setting" for each of your ATA controllers. There are 2 settings for your primary and secondary ATA controllers -- "DMA if possible" and "PIO only". If your controllers are set to DMA if possible (default), then you will see an "Ultra DMA Mode" textbox under the combo that you use to select the mode. This means that you are using the maximum available throughput for your controller. The possible things you can see in the textbox are:
- Ultra DMA Mode (DMA/66, DMA/100)
- DMA Mode (DMA/33)
- PIO Mode (PIO Modes 1-4)
* Using the MMC Performance tool for Win2k, you can monitor your disk transfer rates. You can also use performance benchmarks like SiSoft Sandra. Both ATA/100 and ATA/66 maintain speeds of roughly 35-37MB/sec, with ATA/100 having higher bursts.
Enjoy.