Apple Performa 6400/180 - Manual (Page 39)

Basics Dual In-Line Memory Modules (DIMMs) - 37
Dual In-Line Memory Modules
(DIMMs)
The 6400 and 6500 come with 16 MB of DRAM. Two 168-
pin sockets allow for memory expansion.
The 6400 and 6500 use DRAM Dual In-Line Memory
Modules (DIMMs) instead of DRAM Single In-Line Memory
Modules (SIMMs). Whereas SIMMs have 72 pins, DIMMs
have 168 pins. The extra pins provide a 64-bit data path,
compared to a 32-bit data path for SIMMs.