Don -

You're venturing into hazardous places here, I think, although the specs for the Omega don't really look all that hard to meet unless you've got a fairly old laptop(?).

Laptops generally do have slower rotation-speed hard drives than desktop machines, partly because higher rotation speed makes the drives more susceptible to damage when they're jostled about. An additional "slow-down" seems to happen with laptop hard drives since they usually appear to "hard park" the heads between each read/write excursion to keep them off the disks when not actually trading data. Desktop drives often just "float" the heads wherever they end up, waiting for the next transaction. The parking introduces a "latency time" that is ignored by the drive specs, but makes laptops generally as much as 10:1 slower (maybe 4:1 typical) than similarly spec'd desktops for sustained data transfers. The drive specs (what they'll tell you) may read identically, but the laptop drives will be much slower for actual data transfer, especially for "sustained transfer" of large files or large numbers of files.

An external USB hard drive will look, to your computer, just like an internally installed one, so you should be able to record directly to the external one - assuming that the software installed with the Omega lets you choose where to put the data. That may or may not completely eliminate the installed hard drive if the machine buffers data (including drive I/O) on the system disk.

System temp space, used by the computer for "virtual RAM" when needed, may be in the system folder on the internal drive even if you're writing to the external one, so the "latencies" that slow down the laptop internal drive may still not be separated completely from the handling of data intended for the external one.

The Omega spec includes a very low RAM requirement, and if you've got "enough" RAM the temp space location (the "virtual memory" thing) may not be a problem(?) if you can just arrange to not use any.

The spec for a 7200 RPM or better hard drive doesn't seem consistent with the "USB-1 or better" also in the spec for the Omega. USB-1 is a lot slower than USB-2, and it's hard to see why a good 5200 RPM drive wouldn't be able to keep up with typical USB-1 data rates. It's possible that the USB-1 speed is sufficient for getting the data from the Omega to the computer, but the software installed on the computer does some "processing" that requires higher disk speed(?). If you add an external USB drive, you would almost certainly need USB-2 (or better) for the external drive, in order to get any benefit from a faster external drive.

Theoretically, you can mix USB-1 and USB-2 devices on the same computer, and each will operate at it's own best rate - if the computer itself has a USB-2 port capable of both modes and can select the mode separately for multiple devices; but in practice any USB-1 device attached often slows all attached devices down to USB-1 rate - especially with "early USB-2" ports. (If the Omega is itself a USB-1 device, it could slow down a USB-2 hard drive attached to the same port(?); although USB-1 has been obsolete long enough that it's unlikely they'd use one, given their other component specs.)

Since you're using a laptop, the assumption would be that you're planning to be able to "take it out" with you(?). "External USB" IS NOT THE SAME THING as "TRANSPORTABLE External USB." Typical external USB drives are intended for use with desktop machines and DO NOT TOLERATE being moved about, no matter how carefully they're handled. If you're looking for something you can take with you, you should get an external drive that's specifically rated as "transportable." - and then STILL handle it gently.

The specs for the Omega look like it's intended to be "usable" with machines that meet pretty primitive specs, so there's a good chance it will work with what you've got, even if you ignore the disk speed minimum. If you have USB-2 ports on the computer, an external USB drive should act just like another internal one, but a "faster external drive" won't be much faster if it's tied into a USB-1 port, or to an "older" USB-2 port that's locked down to USB-1 speed by other connected devices.

More questions here than answers, but you'll have to do most of the thinking anyway.

John