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ROM and RAM

By rajankanth ·
can we discuss about the thing of ROM and RAM

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what's to discuss?

by Jaqui In reply to ROM and RAM

read only memory = ROM
random access memory = RAM
should be obvious.


edited to fix typo for DE.

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Jacqui, Jacqui It's Read ONLY memory, you forgot your ly

by Deadly Ernest In reply to what's to discuss?

ROM - Read Only Memory is loaded with code at the factory and can't be changed. At one time BIOS chips were ROM chips. The code is burnt into the chip and a change of BIOS meant a new chip, they soon switched to EPROMS for BIOS.

RAM - Random Access Memory is dynamic and used by the computer, the memory stays in place only while an electrical charge is passed through it.

Another common memory is the EPROM - Erasable Programmable Read Only Memory - this is placed in a UV source and the coding is erased, you can then cover the access window and load new coding into it with a special burner. At one time nearly all BIOS chips were of this type, most 386 486 and P1 BIOS chips. The current BIOS chips are developed from this type of memory, the erase method is different now.

Edit to fix typo.

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yup

by Jaqui In reply to Jacqui, Jacqui It's Read ...

a typo

and the cmos data for the bios is what gets the updates and changes, the chip itself is always what the factory sent out.
[ which is why the tamed trojan killcmos will reset the bios to factory when run, it does exactly the same as switching the jumper around does. ]

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OK I don't design modern chips, but my understanding

by Deadly Ernest In reply to yup

based on decades of experience and reading is:

1. BIOS chip has the Basic Input Output System information on it. This chip used to be a ROM chip, then became an EPROM. The modern ones are reprogrammable by Flash Programming. When you use the special Flash program and load the new BIOS upgrade, it erases the old one and loads the new one, and then acts as a ROM again.

2. CMOS is a low power RAM chip that is kept alive by the CMOS battery. It stores the individualised setting information that you entered into the BIOS when you set the system up. This fine tunes the info in the BIOS, it does not change what is stored in the BIOS chip, just the details of what is loaded into the system from the BIOS. Things like date, time, drive settings, boot order etc.

You can clear the CMOS by removing the battery, or letting the battery get flat.

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essentially

by Jaqui In reply to OK I don't design modern ...

yup.

but there is a jumper that will clear the cmos data if changed.

and killcmos actually wipes the cmos and bios, including any updates, back to factory.

the bios is stored on two chips, one is an eprom, the other is a rom, you can always get back to the original factory bios. This is because of the known bios viruses, they had to have a non corruptible bios version on the boards.

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Any BIOS chip that can be "flashed"

by NickNielsen In reply to Jacqui, Jacqui It's Read ...

is an EEPROM - Electrically Erasable PROM. These have been around since the late 80s.

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There are 2 types

by w2ktechman In reply to Any BIOS chip that can be ...

EPROM and EEPROM
EEPROM is the latest version, and has been in use for many years
EPROM was its predecessor, which led to EEPROM development due to flaws.
That is what I have heard, but I dont remember where exactly. Also, not sure about the flaws themselves.
I was going to bring this up, but you beat me to it.

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The flaw was the erasing bit was done by UV light, and

by Deadly Ernest In reply to There are 2 types

the chip had a window that allowed the light in. After burning it, you placed a sticker over the window. Should the sticker glue be too strong, you couldn't get it off to erase it to reuse. If the glue is too weak, the sticker fell off and the first time any sunlight fell on it, it got erased. Place I worked in the early 1980's used heaps of them, and this was a constant concern.

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