How to Recognize Slotted CPUs
There was a time when slots ruled the motherboard ecosystem. Most modern processors mount directly to the motherboard using some variant on the socket system, instead of going inside cartridges.
What's the Difference Between Athlon and Pentium Cartridges?
The original AMD Athlon introduced in a slotted form factor. This made it possible to do things like add external level 2 cache modules to the processor through a back-side bus rather than having to deal with the shared front-side bus:
- Slot A: Slot a uses a 242-pin physical connector to communicate between the CPU and motherboard over the EV6 interface. This interface and its supporting chipsets was the first to use a double data rate connection at 100 MHz, making it effectively faster than a 133 MHz Pentium P6 bus.
- Slot 1: Slot 1 uses the same 242-pin physical connector as Slot A, but it physically reverses so that the Pentium II cannot fit on an Athlon motherboard and vice versa. Its GTL+ interface runs at the same 100 MHz as the EV6, but only offers single data rate transfers for half the bandwidth.
Why Did They Move Back to Sockets?
The original reason for using Slot a was that the processor cartridge form factor made it easier to include L2 cache in the processor packaging without paying the performance penalty of going through the main chipset interface. AMD had three main reasons for moving back to socketed processors.
- Performance: In order to improve performance, the second level cache moved onto the processor die with the Thunderbird series Athlon processor. This boosted its speed to match that of the CPU, rather than limiting to no more than half the CPU speed, causing a significant performance boost.
- Production: While the SC-242 was simple to construct, a CPU cartridge was far more difficult and time-consuming to manufacture than a single processor die. Shifting back to socketed processors was a huge step in improving manufacturing efficiency.
- Cooling: Because the heatsink and CPU cooler mount sideways over the motherboard, heavier cooling solutions place undue stress on the SC-242 connector that supports the processor. Going back to sockets enables users to securely mount heatsinks directly to the motherboard without stress. This also makes overclocking easier.
What Did the Athlon Mean?
The most important thing the Athlon did was bring competition back into the computer industry, the first to follow after another major brand in the industry. It was a huge step forward for motherboard makers and chipset designers as well, because it gave them two customers to serve and helped prevent a monopoly.
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