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The extra pins were forward-planning, on both Socket 2 and Socket 3. Most of the extra pins are used for power (Vcc) and ground (Vss), which is useful to provide more power to a CPU. The other pins are keys, a new INIT pin (F19), and signals used for enabling and controlling the write-back L1 cache. (See the socket 3 specifications in the 486 family ...

They were most likely wrinkled like that from the start, due to the way they were manufactured, and thus you should not be worried. Until the mid-90s, boards often went through an HASL, or "hot air solder leveling" process that put solder on the traces before the solder mask (a protective layer over the board) was applied. This initial solder over the PCB's ...

Preface The question is a bit unclear(*1) about the margins set regarding: Must it be a single motherboard or do separate assemblies qualify? Must it be PC-compatible or does any x86 system qualify? Must the board have been available separately (to the general public) or do complete assembled systems qualify? So answers do vary a lot depending on what ...

Most of the reference material for the Apple II that I have seen refers to the 4116 RAM chip which held 16x1 kbit. Jup, at the time the Apple II really took off, 4116 chips had already dropped to less than twice the price of 4104, making any use of 4104 impractical. Not many were delivered using 4104, and while some users may have had 4104, they all soon ...

If you’re looking specifically for motherboards directly supporting multiple x86 CPUs, in a multiprocessor configuration, and available for purchase outside the system they were designed for, a likely candidate for the first such motherboard is the Gigabyte GA-586ID, which supported two socket 5 Pentium CPUs in an SMP configuration. It was released in 1994. ...

Well, it could easy be a socket for a 387 type FPU. Size and number of pins would fit a 387 (or some pin compatible Cyrix FastMath) as PLCC carrier. On the other hand it's rather unusual to place it far from the main CPU, seen in the lower left. But without more information it's hard to say. Maybe some sharp close up can reveal markings supporting this?

The following information comes mainly from pages 70-72 of the Apple II Reference Manual, 1979 edition. The Apple II had three rows of eight sockets for DRAM: rows C through E from front to back. Each row could accept either 4116 16Kbit×1 or 4104 4Kbit×1 DRAM chips. Each row also had next to it a DIP socket for a 14-pin "memory configuration block" ...

Socket 3 did not have more pins than needed. It was designed to support the Pentium OverDrive CPUs that Intel released in the mid-1990s. These CPUs could have up to 237 pins, while the Socket 3 allowed 238 pins.

This is actually a comment, but images cannot be inserted in a comment, so I wrote an "answer", just to point out that this kind of trace looking is already known in other computers, like the ZX Spectrum. AFAIK, this is due to the wave soldering process used. This is how it looks like on the solder side:

Not a full identification, but a hint from the chipset: It's an Acer (ALI - Acer Lab Inc) M1429, a somewhat late (1993+) ISA/VLB chipset for 386 and 486 systems. South Bridge is M1431 of the same series. Sometimes called Aladdin II as well. This chipset was extremely common for low-end 386/486 consumer boards with VLB, back then, and Acer sold them to ...

If you expand the criteria to include systems where the two CPUs are not on the same circuit board, the Intel ISBC 86/12 from 1979 is a Multibus-compatible single board computer. Later, the Compaq SystemPro from 1989 supported up to two 33 MHz 386 processors, also on their own cards, and could run Windows NT 3.1, but this version of SystemPro only supported ...

The DEC Rainbow (1982) was built with two CPUs on the motherboard. One was an 8088 and the other was a Z80. It could run 8 bit CPM, 16 bit CPM, or MS-DOS. When running MS-DOS, the 8080 was used as an I/O processor for disk access. This doesn't quite fit your criterion, because only one of the two CPUs was x86, and because there was no OS that allowed ...

Original Apple II Rev 0 with 4K memory select blocks and 4K memory chips also pictured is an original Datanetics keyboard.

Does an Apple II motherboard count? Back circa early 1981, I used a design similar to that of the Z80 Softcard to prototype an 8088 softcard that could do asymmetric shared memory multiprocessing with the 6502 in an Apple II. Used it to demo using the 8087 as a math accelerator for the Apple II. Jobs was unimpressed, but didn’t fire me.

Some points that came in as comments support that this is likely due to a "just in case" design that would allow for heat sinking the packages through the motherboard if the need should arise. Presumably the additional cost of drilling the unused holes is minimal, whereas unnecessarily screwing down the packages, probably adding manual steps to the ...

AFAIK there is just one 14.318MHz crystal (not an oscillator) on the 5150 motherboard, right next to the 8284. It’s a flat metal component with two leads coming out of it from one side, probably marked with 14.318MHz. There might be a solid wire soldered to its housing, going across it. I’m pretty sure it was labeled as Y1 on the PCB.