Running on one SIMM

[CTho9305]

I was under the impression this was impossible, but an HP vectra my friends and I are rebuilding seems to boot AND RECOGNIZE the full 16 meg SIMM. you can load OS'es and everything. How is that being done???

 

[IamDavid]

Ummm, did you see this for yourself or did they tell you about it?

 

[AndyHui]

SIMMs are only required to be in pairs on Pentium motherboards.

A Pentium has a 64-bit datapath to RAM; SIMMs only provide a 32-bit datapath. 2 SIMMs are put together and multiplexed to get the 64 bit datapath.

A 486 only has a 32-bit datapath and can run with a single SIMM.

The other possible situation is that there is already RAM soldered to the motherboard. In such a case (with Pentium motherboards) I have seen it possible for just one SIMM to be present.

 

[Gunbuster]

Some pentium mainboards were designed to double bank a single SIMM it worked but was very slow
CTX was the main offender back in the day

 

[CTho9305]

<< SIMMs are only required to be in pairs on Pentium motherboards.

A Pentium has a 64-bit datapath to RAM; SIMMs only provide a 32-bit datapath. 2 SIMMs are put together and multiplexed to get the 64 bit datapath.

A 486 only has a 32-bit datapath and can run with a single SIMM.

The other possible situation is that there is already RAM soldered to the motherboard. In such a case (with Pentium motherboards) I have seen it possible for just one SIMM to be present. >>



thanks, i didn't know that.

IamDavid - i used it myself

 

[CZroe]

My friend's Acer computer had a custom mobo that could "Double-Bank." It was some form of AT/ATX hybrid with a mobo power switch (ATX), but an AT PSU and PS2 ports in a row on the back (ATX) and a riser card with ISA and only 1 PCI slot (NLX?).
Weird how someone goes through the engineering to make something like this, but the user manual still says you have to upgrade in pairs (?). I never knew 'till some guy gave him a bucket of old SIMMs and he started popping them in with abandon (He doesn't know what he's doing, but "It worked" he told me, which I didn't believe untill I saw it). Some of the SIMMs were faulty though and wound up permanently screwing his computer when he's always missing 1MB from three of his SIMM slots (Yeah, it's weird like that). He swapped the bad one around into three different slots trying to find out why it said he had 63MB until he noticed it then said 62 and then 61, even with known good RAM so it permanently fried an ~1MB address range or something.

 

[Whitedog]

Was it a 486? Just curious... you never mentioned that part.

 

[CTho9305]

<< Was it a 486? Just curious... you never mentioned that part. >>



oh. yeah, 486. the heatsink says its an sx 33 overdrive... the bios calls it a 66mhz overdrive. i have no clue what it is, except that it is some type of 486.

 

[CZroe]

My friend's was an AMD K5 PR166 (133Mhz, "Pentium rated" at 166)
But, more importantly, it was a Socket 7 board (Late generation Pentium compatible).