Timeline for Why isn't the BIOS' ROM chip made using CMOS technology?
Current License: CC BY-SA 4.0
5 events
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| Jul 10, 2018 at 1:14 | comment | added | Jules | ... also because the entire system was designed before flash was commonly available, so the BIOS was stored in either PROM (which uses fuses to determine whether each bit is a 1 or 0, and can only be changed from 1 to 0 but not back again) or masked ROM (which uses a layer of metal wires overlaid over the chip to program it and can't be modified at all after manufacture), so a separate device was necessary, and everything has needed to retain backwards compatibility since then. | |
| Jul 9, 2018 at 15:11 | comment | added | rackandboneman | @Kais because a flash memory cannot be arbitrarily overwritten, and managing rewriting whole pages of flash memory complicates things in an error-prone way. Also, there are things like event logs stored by some BIOSen, this comes with the hazard of wearing out your flash and/or ending up with corrupted data if the power fails in the wrong moment. True EEPROM memory would be possible - but a) it is SLOW to write, and b) you have a low-power battery for the clock anyway. | |
| Jul 8, 2018 at 17:46 | comment | added | user6039980 | "If you're asking why the BIOS isn't stored in volatile RAM rather than nonvolatile flash, that's because batteries fail" No, I mean the opposite - why the information on CMOS chip isn't stored in the BIOS flash. | |
| Jul 8, 2018 at 17:45 | comment | added | user6039980 | "So in a sense, your question is based on an invalid premise — the flash EEPROM is CMOS" - The phrase "Programs are stored on the system BIOS chip, while the changeable data is stored on a CMOS" confused me a bit, now I have understood. | |
| Jul 8, 2018 at 16:59 | history | answered | Dave Tweed | CC BY-SA 4.0 |