4 ms·

I believe it was in the mid-2000s that BIOSes started storing configuration data in the same SPI flash they occupied, and UEFI just continued that trend and exp

I believe it was in the mid-2000s that BIOSes started storing configuration data in the same SPI flash they occupied, and UEFI just continued that trend and expanded on it. That removing the CMOS battery no longer clears it automatically is both a good and bad thing, and another problem it's created is that flash has a limited number of write cycles - and every time the system is booted, and possibly even while running, writes occur.

Crosseye_Jack 2y ago
> another problem it's created is that flash has a limited number of write cycles SPI flash typically have somewhere between 10k to 100k write cycles. Without wear leveling, lets say a write is made on every boot, and lets say a machine is booted 3 times a day you are still going to have a 9+ year life on a flash chip with only 10k writes. EDIT: Did a search for a random "replacement SPI flash MSI" and found an MX25L25673G being used. Using that as an example it has 100k write cycles, using 3 writes a day, that's like 91 years. Basically flash memory is at the point where its "good enough" not to worry about.
- Cthulhu_ 2y ago
  While I agree this is good enough for 99% of purposes, it is a good thing to keep in the back of your head if you're doing e.g. archival or restoration work. I want to believe that in a hundred years, a PC museum employee finds this post and knows what they need to do to get their ancient 2025 era PC back up and running.
  - Crosseye_Jack 2y ago
    Well if long term archival is your concern, its not the write cycles you want to worry about (I was using an extreme example for a bios flash ic) but bit rot in general, which is a concern for pretty much every type of digital media. Spinning rust can seize, Optical and tape media can physically decay, flash media cells can gradually lose their electrical chare over time if they are not “exercised”. Edit: however its not unheard of for SPI flash to have specs of 500k write cycles and a 100 year data retention (below 500k write cycles) these days, so if a 2025 machine was using such a chip you just got to make sure the caps don't leak and erode the PCB, or the thin layer of epoxy bonding the multiple layers of the PCB breaking down causing it to delaminate.
kiney 2y ago
its a bad thing. Nothing good about it.
- zettabomb 2y ago
  It's helpful to not have to reconfigure everything after the battery inevitably runs out. Especially with more modern UEFI systems, there can be quite a lot of options which you might not remember the correct setting of.
gogusrl 2y ago
I found an point-of-sale minipc with a very nice integrated touchscreen (Pipo X10). As I kept getting unrecognized usb device on a usb-serial adapter I entered bios and played with a few usb-related bios settings. Save & Exit and I discovered I just disabled ALL my usb ports with no way to reset the bios or any other available port to plug an input device into. So yeah, the CMOS battery not clearing the bios + my own stupidity cost me ~150$.
- fensgrim 2y ago
  Looks like its easy to wipe and flash the bios chip by CH341A plus a couple diodes to get voltage down to 1.8V, likely without desoldering it too; yet finding the bios image seems to be somewhat impossible due to byte rot (adding extra steps to dump the image with the CH341A, locate the start of data blocks, wipe them).

Crosseye_Jack 2y ago

> another problem it's created is that flash has a limited number of write cycles SPI flash typically have somewhere between 10k to 100k write cycles. Without wear leveling, lets say a write is made on every boot, and lets say a machine is booted 3 times a day you are still going to have a 9+ year life on a flash chip with only 10k writes. EDIT: Did a search for a random "replacement SPI flash MSI" and found an MX25L25673G being used. Using that as an example it has 100k write cycles, using 3 writes a day, that's like 91 years. Basically flash memory is at the point where its "good enough" not to worry about.

Cthulhu_ 2y ago
While I agree this is good enough for 99% of purposes, it is a good thing to keep in the back of your head if you're doing e.g. archival or restoration work. I want to believe that in a hundred years, a PC museum employee finds this post and knows what they need to do to get their ancient 2025 era PC back up and running.
- Crosseye_Jack 2y ago
  Well if long term archival is your concern, its not the write cycles you want to worry about (I was using an extreme example for a bios flash ic) but bit rot in general, which is a concern for pretty much every type of digital media. Spinning rust can seize, Optical and tape media can physically decay, flash media cells can gradually lose their electrical chare over time if they are not “exercised”. Edit: however its not unheard of for SPI flash to have specs of 500k write cycles and a 100 year data retention (below 500k write cycles) these days, so if a 2025 machine was using such a chip you just got to make sure the caps don't leak and erode the PCB, or the thin layer of epoxy bonding the multiple layers of the PCB breaking down causing it to delaminate.

kiney 2y ago

its a bad thing. Nothing good about it.

zettabomb 2y ago
It's helpful to not have to reconfigure everything after the battery inevitably runs out. Especially with more modern UEFI systems, there can be quite a lot of options which you might not remember the correct setting of.

gogusrl 2y ago

I found an point-of-sale minipc with a very nice integrated touchscreen (Pipo X10). As I kept getting unrecognized usb device on a usb-serial adapter I entered bios and played with a few usb-related bios settings. Save & Exit and I discovered I just disabled ALL my usb ports with no way to reset the bios or any other available port to plug an input device into. So yeah, the CMOS battery not clearing the bios + my own stupidity cost me ~150$.

fensgrim 2y ago
Looks like its easy to wipe and flash the bios chip by CH341A plus a couple diodes to get voltage down to 1.8V, likely without desoldering it too; yet finding the bios image seems to be somewhat impossible due to byte rot (adding extra steps to dump the image with the CH341A, locate the start of data blocks, wipe them).