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Memory
The ThinkPad computers use the following types of memory:
Read-only memory (ROM)
Random access memory (RAM)
Real-time clock/complementary metal-oxide semiconductor RAM
(RT/CMOS RAM)
ROM Subsystem
The ROM subsystem consists of four banks of 128 KB memory.
ROM is active when power is turned on and is assigned to the top of
the first and last 1 MB of address space (hex 000F0000–000FFFFF
and hex FFFF0000–FFFFFFFF). After POST checks that system
memory is operating correctly, the ROM code is copied to RAM at
the same address space, and ROM is disabled.
RAM Subsystem
The RAM subsystem on the system board starts at address
hex 00000000 of the address space. The RAM subsystem for the
ThinkPad 770 is 64 bits wide.
The 32 MB base memory is on the system board. Two 144-pin
8-byte dual inline memory module (DIMM) connectors are provided
on the system board. Both connectors accept an 8 MB, a 16 MB, a
32 MB, a 64 MB, or a 128 MB DIMM. The memory capacity can be
increased up to 256 MB. When two 128 MB DIMMs are installed,
the base 32 MB memory on the system board becomes inoperative.
The total amount of usable memory is less than the amount of
memory installed because of ROM-to-RAM remapping and power
management.
2-16 System Board