Before buying aforementioned hard disk I wanted a suggestion that will it work .
I have windows xp & my processor is 1Ghz,384MB RAM.
I heard that a computer can access limited size memory decided by BIOS. Is that just for internal disk ?
Is there no limit on memory size of USB powered disks ?
Hard disk inside my CPU is PATA & it is around 10 years old. It cannot boot from USB , that old.
I know that a USB port can provide 500mA so I think 1TB will draw power from 2 ports.
If somebody has CPU of this or lower specs & has been able to use 1TB USB hard disk . Please tell , it will be assuring.

Sorry, this question isn't about any linux distro . I just wanted expert advice on hardware.

I thought that the case was limited as far as booting the drive.
Grub related.

You are confusing memory (a.k.a. RAM) and diskspace. You can use any harddisks of any size on USB. If you need 2 ports to power the disk is dependend from the physical size of the disk, 3,5"-disks usually have an external powersupply, so that only one USB-port is used, while the smaller 2,5"-disks usually come with a cable that has two USB-connectors on one side for the supplying power.

The only drawback to mounting an external HD on a P111 is that the USB port is probably v1.1

You'll only get 12mb transfer rate. Big difference from the 400mb rate of USB 2.0
Transferring data to and from will be a little slow.

Some file systems will only allow limited partition sizes. Like fat, fat32 etc. So you can't have a 1TB Fat volume.

Most 3 1/2 in. external drives have a power adapter that powers them. There are also powered and non powered USB ports. You'll have to see what you have.

In my CPU there was no USB port then I got internal modem (PCI card) by chip for USB(2.0)

I bought 1TB hard disk .
It has external 220V plug for power & a USB port to computer.
It works without a hitch at max speed of 10-12MB/s.
Theoretical limit is 80MB/s.
USB 3.0 promises 4.8Gbit/s i.e 10 times of 2.0 version

If you are in control , you aren't going fast enough.