UEFI BIOS Option

I have two options (CSM) or (UEFI) in my Toshiba Laptop BIOS. When I select UEFI the computer will not boot. I tried to get Toshiba's tech support to explain this to me but besides not speaking english I did not get a clear answer.

If anyone has the time and knowledge to explain this option and it's uses in simple terms I would greatly appreciate it.

Thank You

When CSM (Compatibility Support Module) is enabled it allows a modern EFI based PC to operate in a Legacy BIOS mode.

This allows for your operating system to be installed and run from a traditional MBR (Master Boot Record) disk and the advanced features of the EFI system are disabled.

Switching to UEFI mode enables the EFI system. UEFI PCs usually use the GPT file table, which includes a hidden SYSTEM partition and a Windows SYSTEM RESERVED partition.

I am assuming that what you meant to say is that with UEFI enabled Windows will not start, not that the PC will not boot. (If the PC did not boot you could not get into the BIOS settings to change it back.)

I believe that this is because Windows was installed in legacy BIOS mode. I believe that to run in UEFI mode you would need to reinstall Windows or make some alterations to the startup process. I do not know if Startup Repair would help in this case. Perhaps someone else here will know this and comment.

These systems are relatively new. I do not own one yet, so I have not had the opportunity to play with one to get hands on experience. What I know is what I've read.

Thank You!

It is a Laptop. And it took awhile before I even found out about that setting.

You are correct .. I get a "no bootable device" message when trying to change it.

I plan on putting in a SSD soon but I was not planning a clean install. I just did that to get rid of the bloatware.

So .. as far as I know .. it's ment for a 3 Terabyte hard drive and the GPT table. The SSD I plan on using is 128 Gig.

Thanks again !!

Just one small correction to keep the info straight for everyone.

You need to format a disk GPT to use a partition greater than 2.2TB this is true, but you can format a drive of any size GPT.
Not that you would want to or need to with the SSD, just that you could.

My daughter's laptop has a 750GB HDD that is formatted GPT and uses a hybrid UEFI Bios.

Thanks Again,

So .. If I format the SSD to GPT and enable it in the bios. I am guessing I would not be able to clone the current 750 Gig Hd to the SSD but would have to do a clean windows 7 install?

If so would I also need to format the 2nd 1 terabyte Hd to GPT?

Then the UEFI would be enabled and I would gain what?

I'm guessing a GUI interface to access the bios?

Thanks for the replys. I am starting to understand this now, I think.

Here is a link to the laptop -> Toshiba Qosmio X875-Q7290

Rockit said:

Thanks Again,

So .. If I format the SSD to GPT and enable it in the bios. I am guessing I would not be able to clone the current 750 Gig Hd to the SSD but would have to do a clean windows 7 install?

If so would I also need to format the 2nd 1 terabyte Hd to GPT?

Then the UEFI would be enabled and I would gain what?

I'm guessing a GUI interface to access the bios?

Thanks for the replys. I am starting to understand this now, I think.

Here is a link to the laptop -> Toshiba Qosmio X875-Q7290

No, not all correct.

From what I understand, if the BIOS is set to UEFI mode and then you install Windows 7 the installer will do all the hard work. It will set up the GPT, create the needed partitions, and install Windows.

I am not sure if you can alter an existing legacy BIOS installation to work on a UEFI BIOS, I don't have that experience. But I'm pretty sure cloning would be a no.

You do not need to create GPT on any other data drives. That is only necessary if you want partitions that are larger than 2.2TB. The extra drives can be MBR and work fine alongside the GPT disk and vice-versa.

Note that any and all partitions created will still be formated NTFS. That does not change.

UEFI will be enabled only by doing so in BIOS Settings. You do not gain anything immediately by doing so. It is probably not worth the effort if the laptop is all set up. If I can dig up an article explaining the benefits of a UEFI system I will do so (no time now). The GUI interface is not automatic. That has to be set up by the manufacturer. Most laptops use a hybrid BIOS - a UEFI platform but a legacy BIOS interface. I don't know if this can be changed or upgraded.

But if it's a new laptop I would not go changing things just yet. I would only make that change to gain something tangible.

Are we having fun yet?

I'm probably confusing things here, I have a board that only has UEFI available, no legacy BIOS. It is a really nice GUI where you can navigate with the mouse and keyboard. UEFI is also supposed to be more secure against threats infecting the board, I think.
Most UEFI systems allow the user to take a screenshot of the display with a USB drive attached by pressing F12 too.

My drives, SSD for OS, HDD for AppData and Users, are bot MBR partitions.

Thanks for that Britton.

Some other benefits:

• UEFI BIOS boots faster.
• Allows the native use of the GUID Partition Table (GPT)
• Allows for the use of device drivers at the BIOS level - so you can use a mouse in BIOS GUI for instance
• Allows for support of more processor platforms.

Some good reading:
UEFI - About UEFI
Understanding Disk Partitions
Unified Extensible Firmware Interface - Wikipedia, the free encyclopedia
Installing Windows on UEFI-based Computers


Enjoy!