Can't Boot from a 2GB USB flash drive

I have a problem booting from 2GB USB flash drives. I have no problem with
4 GB USBs. I've tried 3 different 2GB flash drives (2 brands Lexar, Toshiba)

Examples include the USB bootable system repair and the Hirens boot USB.
Both are under 500MB! Both are fine with 4GB USBs.

The computer's an Acer Aspire desktop.
I can't see anything obvious in the BIOS settings - I'm totally puzzled.

does bios see it during POST?

The BIOS sees it. I'm bios booting with F12 (in my case) and selecting the USB.
I have an option in the bios which USBs under 2GB as floppies. I have changed this to view all USBs as HDD - still doesn't work. Do exactly the same thing with a 4GB and it always boots.

I realize these are boring questions, but have you tried the created 2GB flash drives in another setup to verify they are actually bootable?

What else could be different between them? Are the 2GB drives being formatted as FAT16 vs 32 for the 4GB?

Ageeb,
No other (computer) system to try but I don't think it would prove that much.
Because these are live boot USBs the BIOS bypasses the windows disk MBR (& disk) all together. So the key elements are I think

BIOS---On board USB controller..................CPU+memory
...........................|
........................USB Flash drive

Still trying to figure it out. Anything windows (eg. System repair disk) works fine on 4GB USB although it only needs 200MB!
On the 2GB USB anything linux works. I have Linux Mint 9 Isadora (800MB) installed boots works perfectly.
Done the usual
Clean, create partition primary, select partition 1, active, format fs=ntfs
+ format fs=fat32.

Comes back with Disk read error occurred - Ctrl+alt+del to restart
(Probably a bios generated error message).
So it looks like something to do with the BIOS and USB controller????

I really can't think of what's not jiving. It would be interesting if you could repartition a spare 4GB as 1x 2GB active partition (rest whatever) and repeat procedure. I agree it has to be BIOS related.

Is there a legacy USB option in BIOS? is it Enabled/Disabled?

Golden said:

Hi Guys,

I think the reason is there is an insufficient amount of space on a 2GB USB for Windows 7 to "unpack" the installation files - it requires some temporary working space too.

As far as I am aware, to install from USB, the mimimum size is 4GB. See this tutorial Windows 7 USB/DVD Download Tool

Regards,
Golden

I don't recall it being a specific problem to creating a windows 7 USB installer. Or I misunderstood something...

mjr said:

Examples include the USB bootable system repair and the Hirens boot USB.
Both are under 500MB! Both are fine with 4GB USBs.

Golden,
The Windows 7 installer I think you're referring to is for the full deal - OS. I'm talking about the system repair dvd which you can install (for convenience) on a USB and is of the order of 200MB.

I used Partition Wizard to create a lot of unallocated space on the (system repair) bootable usb, leaving around 700MB. Booted fine. But then that's probably to be expected since a 4GB USB is still detected.

If I flip the bit on a 4GB USB it will change it to removable HDD which can be partitioned. But I don't think it's really proving much.

There is a setting in the (AMI) BIOS which treats a USB like a HDD or a floppy. In the auto mode (default) anything less than it 2GB treats like a floppy anything greater than 2GB is treated as a HDD. I changed this mode to HDD for all sizes before posting the problem.