Check if Centris 650 has a fpu or not

[zoo]

Found a Centris 650 online. I read on wikipedia that the base model does not come with fpu. But I want to run A/UX on it, how would I go about asking a seller about that? Or are there any good tells from the exterior that it has an fpu? Pictures in this ad here:

Macintosh centris 650

Utropspris: 1500 kr. Typ: Auktion. Slutar: 2025-03-03 18:06:10. Köp & sälj begagnade & oanvända Övriga retrodatorer på Tradera.

www.tradera.com

 

[phunguss]

Hello,

Based on the photos in the listing, it says 16MB of RAM, and one RAM slot is populated. I don't know if a 12MB SIMM exists, so I assume it is an 8MB SIMM in the socket and 8MB on the motherboard... leading me to believe the FPU is integrated. There are 2 SIMMs in the Video RAM slots, so that is upgraded as well.

** O D D D U C K ** - In the photos, it appears there are 5 RAMS slots, all other references only show 4. So this is either a prototype, or somebody has done some work to it. Most references show the 4 RAM slots and an unpopulated pad area next to them where this 5th one appears. It appears that this 5th slot is a ROM socket. Being this listing is from the EU, maybe someone added that socket and did some experimentation on it. While this reference says "Most Centris/Quadra 650's have an unpopulated ROM SIMM socket (but not all, some early models have a socketed ROM)", which may mean it is an early model, I still believe it has 8MB on the motherboard and has an integrated FPU.

References:
Apple Centris 650 Specs (4 RAM slots, 2 Video RAM slots).
EveryMac Centris 650 (Says "**The entry-level M1207LL/A configuration has an 68LC040 processor, which does not have an integrated FPU.") I assume that "entry level" means the motherboard with 4MB of RAM built in.
Low End Mac Centris 650 (shows the motherboard with 4 RAM slots).
Apple-History listing 4 RAM slots.
Wikipedia listing the 5 different models.
Another motherboard photo showing the empty 5th RAM slot pads.

 

[zoo]

Thanks. I agree. The 230MB original Apple drive points in the same direction. It was for the higher spec models.

The ROM-socket is a funny one, since it is obviously running with it unpopulated it uses soldered on ROM. I wonder if I can just populate the socket with a ROM and it runs it from there. It can be a funny machine then....

 

[mdeverhart]

This unit has the on-board Ethernet (connector to the right of the SCSI port), which I’m 99% sure means it has the full 040 with FPU, rather than the LC040 without.

 

[dougg3]

The ROM-socket is a funny one, since it is obviously running with it unpopulated it uses soldered on ROM. I wonder if I can just populate the socket with a ROM and it runs it from there. It can be a funny machine then....

Some earlier models had the socket populated even though there were also onboard ROMs. My guess is they were trying to future-proof just in case there was a nasty ROM bug, and they stopped populating it after they were confident the ROM was good. Just a guess though.

Apple designed it so that installing a ROM SIMM will automatically disable the onboard ROM chips, although a lot of hobbyist ROM SIMM designs don't do it properly because they were designed based on the SE/30 and II series circuit, and Apple slightly changed how it worked with the Quadras. More info here.

 

[zoo]

I won the auction, no other bidders. And it works fine, A/UX and all. Thanks for your feedback all, without it I wouldn't have dared to buy it.