Memory Module (Ddr-Dimm) Slots - Sony PCV-RX640 System Reference Manual

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VAIO Digital Studio System Reference Manual

Memory Module (DDR-DIMM) Slots

Both sides of each Double-data rate, Dual Inline Memory Module
(DDR-DIMM) look very similar. The side with pin 1 has a small "1" to the
left of pin 1. Be sure to orient the memory module correctly in the
DDR-DIMM slot (a small triangle on the slot indicates pin 1).
Memory module (DDR-DIMM)
1 1 1 1
Indicates pin 1