BIOS software is save on a non-volatile ROM chip top top the motherboard. ... In contemporary computer systems, the BIOS contents are stored on a flash storage chip so the the contents can it is in rewritten without removing the chip native the motherboard. This permits BIOS software program to be conveniently upgraded to add new features or resolve bugs, yet can make the computer system vulnerable come BIOS rootkits.

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Since ROM way Read-Only Memory, why have the right to the BIOS materials be rewritten?

Does the "flash storage chip" median the same as the "non-volatile ROM", both an interpretation where BIOS is stored?

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edited may 24 "15 at 21:04

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asked jan 26 "14 in ~ 16:14

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To add to Varaquilex"s answer, the BIOS software application is stored in one Electrically Erasable and also Programmable ROM (EEPROM) which allows firmware to update to be performed electronically. Really old BIOS chips were in reality UV-EPROM chips which required erasing through UV irradiate exposure before they might be reprogrammed.

Edit: As has actually been mentioned in the comments, even previously than that single use Programmable ROM (PROM) chips were sometimes used which might not it is in reprogrammed in ~ all once configured and also required finish replacement to upgrade (although this was hardly ever required).

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edited jan 27 "14 at 2:03
answered jan 26 "14 at 16:23

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ROM is review only, therefore why is the BIOS materials can it is in rewritten?

BIOS program chin is save in an EEPROM (which have the right to be lectrically rasable and

rogrammable) or a flash-memory. So the read-only here is about the chip gift non-volatile. The contents of the storage stays when the power is reduced off, unlike volatile RAM. The ROM being EEP helps the BIOS deserve to be re-written or updated. Back then for such operations, you had to remove the BIOS chip indigenous the board, put a new one (if its not PROM or EPROM), or if the EPROM you have actually to obtain it come the manufacturer and let them re-program the chip and re-attach it come the board. After the existing advances, many thanks to EEPROMs, you execute not need to remove chip to carry out such operations, you just make the computer do the project electrically.

Does the "flash memory chip" median the exact same as the "non-volatile ROM", both definition where BIOS is stored?

from Wikipedia:

Flash memory is an digital non-volatile computer system storage tool that can be electrically erased and reprogrammed.

Flash memory was emerged from EEPROM (electrically erasable programmable read-only memory). There room two main varieties of flash memory, i beg your pardon are named after the NAND and also NOR logic gates. The internal characteristics of the separation, personal, instance flash memory cells exhibit characteristics similar to those of the corresponding gates. Conversely, EPROMs had to be totally erased prior to being rewritten, NAND form flash memory may be written and read in block (or pages) i m sorry are typically much smaller than the whole device. NOR kind flash allows a single machine word (byte) to it is in written—to one erased location—or check out independently.

EEPROM and flash memory carry out not refer to same thing: they are two comparable memory species as one is developed from the other and also contain different type/configuration of MOS transistors. However, they space the memory wherein BIOS regime resides.

To deal with another ofradiation I want to mention this CMOS-BIOS relationship:

The BIOS settings room stored in the CMOS chip (which is retained on power via the battery ~ above the motherboard). That is why the BIOS is reset once you eliminate the battery and re-attach it. The same routine runs yet the settings are defaulted. Watch this answer for a detailed view of memories used throughout the booting process.

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To extend the CMOS-BIOS topic, thanks to
Andon M. Coleman, I want to include his comment to the answer:

It is worth pointing out that the BIOS settings execute not have to be save in volatile CMOS memory. There space plenty of embedded systems that save their setups in NVRAM. The just reason computers have gained away with using volatile CMOS over every these year is the they currently had a battery to store the interior real-time clock ticking if the power is off (recall that as soon as you pressed the strength switch ~ above a PC-AT, the literally reduced all strength off come the motherboard). This intended that cheaper volatile memory might be used to store system settings. So that is greatly for historical purposes.