jheronimus wrote:

Why did AMD stop making their CPUs compatible with Intel motherboards starting with Slot A?

I believe Intel patented Slot 1 in an unsurprising asshole move to make sure nobody could release CPUs for it.

appiah4 wrote:

jheronimus wrote:

why did AMD stop making their CPUs compatible with Intel motherboards starting with Slot A?

I believe Intel patented Slot 1 in an unsurprising asshole move to make sure nobody could release CPUs for it.

Isn't Slot A physically just a mirrored (reversed) Slot 1? I mean, they are electrically different, but they are still basically the same parts to cut down costs for the motherboard vendors.

appiah4 wrote:

jheronimus wrote:

why did AMD stop making their CPUs compatible with Intel motherboards starting with Slot A?

I believe Intel patented Slot 1 in an unsurprising asshole move to make sure nobody could release CPUs for it.

Nope, at least that's not the prime reason. AMD based a lot of the Athlon design on the DEC Alpha 21264 EV6. The EV6 had a bidirectional 64b DDR system bus, so that's what AMD implemented on the Athlon. It offered twice the bandwidth of Intel's SDR FSB, so was technically superior. Additionally the Athlon had a completely different cache architecture compared to Intel's 686 design, so even if using SDR signalling on the bus for backwards compatibility had been considered, it still would not have been possible. The whole question of licensing the 686 FSB or the Slot1 form factor never came up.

jheronimus wrote:

why did AMD stop making their CPUs compatible with Intel motherboards starting with Slot A?

I think, that Wikipedia make a good summary of this:

Wikipedia wrote:

While AMD had previously always used Intel sockets for their processors, Socket 7 was the last one for which AMD retained legal rights. Intel had hoped by discontinuing Socket 7 development and moving to Slot 1 that AMD would be left with an outdated platform, making their processors non-competitive. By extending the FSB from 66 to 100 MHz, Super Socket 7 gave AMD the stopgap solution they needed while developing their own independent motherboard infrastructure, Slot A.

jheronimus wrote:

Isn't Slot A physically just a mirrored (reversed) Slot 1? I mean, they are electrically different, but they are still basically the same parts to cut down costs for the motherboard vendors.

VIA had a deal with intel concerning socket 370. So I figure that without such a deal, it would have been illegal for AMD to make processors for intel socket 370 and Slot 1.

Source - Legal issues
On the basis of the IDT Centaur acquisition,[5] VIA appears to have come into possession of at least three patents, which cover key aspects of processor technology used by Intel. On the basis of the negotiating leverage these patents offered, in 2003 VIA arrived at an agreement with Intel that allowed for a ten-year patent cross license, enabling VIA to continue to design and manufacture x86 compatible CPUs. VIA was also granted a three-year period of grace in which it could continue to use Intel socket infrastructure.