• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

CMOS ram/RTC past and present

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.


Premium Member
Dec 6, 2010
CMOS ram chips.

This is the 1st CMOS ram/Real Time Clock chip.

This CMOS ram/RTC chip has built in battery and crystal.

This is a DIP through hole 8 pin CMOS ram/RTC chip

SMT version

I don't know if the last 2 are used on PC MB's as some time in the past the CMOS ram and RTC was moved to the chipset but I like to think that some manufacturers might be using them.
Last edited:
May we ask why you want to know this information?
For grins, like this one?

For grins, like this one?

Yes, I've been in to computers from the late 70's and have seen the progression of computer tech and just thought I would show how the BIOS and the CMOS/RTC have changed over the years.
Here is a bit more, back in the late 90's with the AMD K5/6 and Pentium MB's I found where the RTC/CMOS ram is located, it's in the SIS 5595 North Bridge/South Bridge chip (see pic)
Integrated Real Time Clock(RTC) with 256B CMOS SRAM in the SIS 5595 chip.

Last edited:
I don't recall any issues with chipsets :), anyway regardless of the manufacture, the RTC/CMOS ram was moved in to the chipset in the late 90's like 97 or 98 .
wow whata fancy board!
simm's and dimm's! AGP! AT and ATX PSU connectors! DIP switches for the CPU multiplier! COPIOUS AMOUNTS OF DUST!

anyway i had a catastrophic failure of one of those Dallas RTCs. Had one on an an expansion card for an Apple IIe, not sure what the card was but the battery in it ruptured some how while it was in storage and it ate away the traces down to the edge connector and ate a bit of the traces on the main board. it was in storage for a long time because i got it right before i moved out and then i forgot about it.

it was pretty sad, that cards probably worth a ton of money now in the collector market. it was really weird though, it wasnt like a transwarp card it was almost like a SBC
That pic is not mine, I pulled it off the internet, here is 1 of my old MB's, it's a 486 MB, I still have this 1.

Picture 005.jpg
oh interesting, did that board combine the two types of simms to run at once or was it either or?

also VLB, i never had any thing that used it, kinda seemed like a wasted effort

i'll have to snap a few pics of the old stuff i still have when i am diggin around the next few days looking for things to sell/trade at portland retro gaming expo
1st pic has a VLB Video card and VLB IO card, bottom pic is old SB card and modem card.

Picture 003.jpg

Picture 004.jpg