There are actually 6 of them on the motherboard this picture is from. The SIMM slots are less user-friendly than DIMM slots, but luckily, most boards today use DIMM slots. SIMMs are old school. Notice that the SIMM slots are basically symmetrical. Things used to be so unfriendly.
DIMM slots are asymmetrical for easier mounting.
Also, SIMM slots require you to angle the SIMMs and snap them into the socket, an error-prone procedure. All rights reserved.