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Not applicable
Posts: 1
Registered: ‎03-09-2018
Location: US
Views: 853
Message 1 of 3

Ideapad Y700-15ISK unable to start OS in UEFI after updating BIOS

Before I explain my current predicament, please note the following:

- Currently running OS on Legacy (UEFI does not launch the OS after the updated BIOS. It does not read the USB I used to install my OS either, so the only option for me right now is Legacy)

- I am not a PC professional by any means; I am, however, trying to figure things out on my own.


So, long story short:
- The keyboard of my laptop randomly began to crash (after a Windows 10 update a few months ago), causing failure to the whole system. Once it occurs the only option is to turn the Laptop off via Power Button, which in turn fries the hardware. (Event Viewer: Embedded Controller (EC) did not respond...Problem could be in BIOS/Firmware/Hardware)

- Gave my laptop for diagnostics at Lenovo, where they changed the motherboard. The issue remained unresolved.

- I tried re-installing the OS (to Win 10 Pro) from the official website, using Rufus (option 1. MBR partition scheme for BIOS or UEFI). The issue remained unresolved.

- I decided to update my BIOS to the latest version - CDCN54WW  (my previous was CDCN25WW). I followed the installation (no way to get it wrong), after updating the BIOS my laptop turned off and once it turned itself back on it could not start the OS; instead it takes me to the Boot Menu. By entering the BIOS Setup I managed to turn Legacy as the preferred boot method, which is how I got here.

I have yet to see if updating the BIOS has fixed the EC Error. I'd first like to know the following:
1. Does Legacy mode limit my RAM/Processor performance? (make my computer run programs slower compared to UEFI?)

2. How can I switch back to UEFI? I most probably have to re-install the OS; seeing as the Boot Menu can't read my current Rufus USB, do I need to use other settings when creating a bootable USB?

3. Has my BIOS updated successfully? I believe so, since my BIOS Setup shows my current version as "CDCN54WW"; but I do not understand where this issue with the OS came from after the update...



Excuse my poor English.

Not applicable
Posts: 13
Registered: ‎05-10-2017
Location: CA
Views: 655
Message 2 of 3

Re: Ideapad Y700-15ISK unable to start OS in UEFI after updating BIOS

Here is the MS tool to convert from MBR to GPT (UEFI)

Not applicable
Posts: 1,049
Registered: ‎07-13-2010
Location: CA
Views: 643
Message 3 of 3

Re: Ideapad Y700-15ISK unable to start OS in UEFI after updating BIOS

To answer your primary question, there's no measurable performance difference between UEFI and BIOS, apart from boot speed. The basic difference is that in UEFI, the hardware addressing is assigned by the OS, whereas in BIOS, the OS needs to query the BIOS for the IRQs, interrupts, etc. There may be a ram limitation in BIOS, but it's well outside what the onboard chipset could handle anyways.


If you cannot install a UEFI OS, make sure Secure Boot is set to off in the BIOS until the OS has completely been installed, otherwise it'll throw errors.

Tap that kudos button if I helped ^^

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