The Slot 1 socket was a departure from the prior sockets which housed only the CPU chip itself and relied on the installer to affix an appropriate thermal solution to it, and optionally cache on the motherboard.
Instead, the whole assembly of CPU and cooling solution were to be merged into one unit, which could be “plugged in”. This style of CPU was adopted for some Pentium II and Pentium III systems, and came in two variants.
SECC stands for Single Edge Contact Cartridge and the initial variant featured a full shroud around the cartridge edge contacts, and clip retention mechanism. The thermal solution varies depending on the cartridge, and in the case of some small form factor machines, the heatsink and fan were replaced with a larger heatsink instead and relied on system airflow for cooling. The connection pins were a double-row, similar to AGP.
Intel Pentium II SL2YK 300Mhz
This particular cartridge uses the Intel supplied thermal solution, the most common of the type.
Intel Pentium II SL2TV 333Mhz
This one appears to have an aftermarket cooling colution.
A second variant of SECC was made, primarily for Pentium III CPUs where the cartridge shrouds were changed, and the clip retention modified. Most of the SECC2 cartridges I have handled use the stock Intel cooling solution.
Intel Pentium III SL35E 500Mhz
This cartridge is easily disassembled and features a custom passive heatsink with thermal sensor cooling solution for a Compaq computer.
Intel Pentium III SL3E9 533Mhz
This is the default Intel cooling solution.
Inside the SECC
SECC cartridges can be taken apart, sometimes non-destructively for SECC and almost certainly destructively for SECC2 (due to plastic retention clip mechanism which likes to snap when disassembled). This is particularly useful when upgrading SFF SECC based systems where custom cooling solutions are used, and you need to transplant the PCB from a SECC2 into the previous SECC shell to use it.
As a result, I had a few unidentified PCBAs from SECCs.
I believe this is a Pentium II based SECC PCBA. The CPU itself appears to be a BGA version of a regular Socket 370 CPU, however, flanked by two cache chips running at half clock-rate and a Tag RAM chip marked SL2WF on the rear.
This one appears to be a more recent, possibly early Pentium III (about 500Mhz) based PCBA. Note the smaller package of the CPU, and the same sort of cache arrangement, although both chips are now to one side.
I’m not sure about this one, but it possibly is either a late Celeron or even a Pentium III chip. The lack of cache on the PCB indicates either no cache (Celeron) or cache integrated on-die as the later Pentium III models had.
The limited amount of choice in SECC CPUs, as well as the (generally) fixed cooling solutions meant that enthusiasts were generally left without an upgrade path once SECC was abandoned in favour of Socket 370. However, SECC is electrically compatible with Socket 370 at some level, and hence adapters (referred to as Slotkets) were available that provided a Socket 370 socket, allowing for Socket 370 CPUs and cooling solutions to be used in Slot-1 motherboards provided the BIOS supported it. However, due to the weight of the solution, mounting and securing could be awkward.
370CPU Rev 1.0 Generic Slotket
AC01 Ver 1.1 Generic Slotket
And here is a Socket 370 CPU sitting in the socket. A thermal solution (i.e. heatsink) has to be clipped over this before it is usable.
Higher end Slotkets were configurable, and featured jumpers to signal the motherboard as to what multipliers and bus speeds should be used, allowing for overclocking.