Do the 3.3V Pentiums work on 3.4V? \ VOGONS

Do the 3.3V Pentiums work on 3.4V?

Topic actions

Post a reply

First post, by demiurge

Posted on 2024-01-21, 03:56

demiurge Offline

Rank Newbie

Rank: Newbie
Posts: 80
Joined: 2024-01-21, 03:06
Location: Onterrible

So I am a new member of the retrocomputing scene and my collection was just sound and vga cards until I needed some test benches.

I bought this ABIT AB-PG5 because it is the only system built for an obscure VGA card.

The system came with an MMX Pentium which uses a 3.3V core voltage. However, the motherboard only lists a 3.4V option and a 3.5V option.

I know it is it within 3.3V±5% below 3.465V is this intended for this motherboard?

AFAIK there were no 3.4V CPU made. Does the extra voltage degrade the chip?

This motherboard clearly had an intent of having a lower voltage, but why wouldn't there be a 3.3V option instead? It doesn't make sense that there were only for overclocking options for 3.3V chips.

I have been looking for a copy of the manual but the internet doesn't have it indexed and the ABIT FTP never had it. So if someone could dig that up for me that would be great.

Reply 1 of 7, by majestyk

Posted on 2024-01-21, 07:30

majestyk Offline

Rank Oldbie

Rank: Oldbie
Posts: 1352
Joined: 2020-12-04, 09:13

Are you sure it´s a Pentium MMX 3.3V single voltage CPU? (I cannot remember having seen one.)
MMX usually are 2.8V core voltage, so if this is the case, you would indeed overvolt it @ 3.4V.

If it´s a regular - non MMX - 3.3V Pentium, the 3% "overvolting" at 3.4V will not hurt it.

Reply 2 of 7, by mkarcher

Posted on 2024-01-21, 08:39

mkarcher Offline

Rank l33t

Rank: l33t
Posts: 2618
Joined: 2019-01-19, 16:29
Location: Germany

majestyk wrote on 2024-01-21, 07:30:

If it´s a regular - non MMX - 3.3V Pentium, the 3% "overvolting" at 3.4V will not hurt it.

Also, the MMX pentiums are "split voltage", with a "core voltage" of 2.7 or 2.8V, and an "I/O voltage" to communicate to the mainboard. The I/O voltage of the MMX processors is the same as the core voltage of the classic Pentium processors, and may be 3.3V to 3.6V (some processors required 3.45V to 3.6V). The jumper that configures the single voltage of Pentium processors usually also configures the I/O voltage of Pentium MMX processors, and supplying 3.4 volts at that place is perfectly fine.

Reply 3 of 7, by dionb

Posted on 2024-01-21, 10:39

dionb Offline

Rank l33t++

Rank: l33t++
Posts: 5765
Joined: 2017-12-23, 15:35
Location: Amsterdam

This board doesn't support split voltage, so that 3.4V/3.5V is fed to the core too.

The only Pentium MMX that supports that is the Overdrive. If this is a non-overdrive MMC it's being overvolted by at least 0.6V, which is over 20% and so and way out of spec.

The P55C core is so robust it (pretty uniquely) can survive that for a while, but it's not good and will shorten the lifespan of the chip, particularly if cooling isn't optimal.

Reply 4 of 7, by demiurge

Posted on 2024-01-21, 13:28

demiurge Offline

Rank Newbie

Rank: Newbie
Posts: 80
Joined: 2024-01-21, 03:06
Location: Onterrible

Thanks all for the replies

majestyk wrote on 2024-01-21, 07:30:
If it´s a regular - non MMX - 3.3V Pentium, the 3% "overvolting" at 3.4V will not hurt it.

That is something that was a bit confusing to me on the meaning of split voltage. The board has only two voltage options for "CPU" and I have no idea if that is just I/O voltage

dionb wrote on 2024-01-21, 10:39:

This board doesn't support split voltage, so that 3.4V/3.5V is fed to the core too.

Sounds like I really need to get a 3.5 V CPU in there sooner than later because 3.3V and split voltage seems to be unsupported.

So this is the CPU https://www.cpu-world.com/sspec/SL/SL27K.html

Attachments

Filename

20240120_203114.jpg

File size

257.95 KiB

Views

339 views

File comment

SL27K

File license

CC-BY-4.0

Reply 5 of 7, by watson

Posted on 2024-01-21, 14:53

watson Offline

Rank Member

Rank: Member
Posts: 101
Joined: 2018-01-05, 12:36

Yeah, that CPU is slowly being cooked at 3.4 V.
Any "regular" Pentium (non-MMX) should be a good replacement.

Reply 6 of 7, by dionb

Posted on 2024-01-22, 17:18

dionb Offline

Rank l33t++

Rank: l33t++
Posts: 5765
Joined: 2017-12-23, 15:35
Location: Amsterdam

demiurge wrote on 2024-01-21, 13:28:

[...]

Sounds like I really need to get a 3.5 V CPU in there sooner than later because 3.3V and split voltage seems to be unsupported.

There's a huge difference between running 3.3V spec CPU at 3.4V (no problem, in spec and actually done quite frequently to improve stability) and running 2.8V spec CPU at 3.4V (long slow toast). Just stick in a 3.3V CPU, it will be fine.

So this is the CPU https://www.cpu-world.com/sspec/SL/SL27K.html

That is a 2.8V CPU requiring split voltage. Don't run that at 3.4V (or 3.3V) for a long time. Any non-MMX Pentium will be fine on this board.

Reply 7 of 7, by demiurge

Posted on 2024-01-23, 02:41

demiurge Offline

Rank Newbie

Rank: Newbie
Posts: 80
Joined: 2024-01-21, 03:06
Location: Onterrible

dionb wrote on 2024-01-22, 17:18:

Any non-MMX Pentium will be fine on this board.

I'm going to go Cyrix just for fun.

Go to top of page Go to top of page

Back to General Old Hardware

Main menu

Common searches