Sony PCV-RX550 - Manuel (Page 60)

VAIO Digital Studio System Reference Manual 48
Memory Module (DIMM) Slots
Both sides of each Dual Inline Memory Module (DIMM) look very
similar. The side with pin 1 has a small "1" to the left of pin 1. Be sure to
orient a DIMM correctly in the DIMM slot (a small triangle on the slot
indicates pin 1).
DIMM1 DIMM2
Indicates pin 1
Memory module (DIMM)
1 1 1 1