IBM 600 manual Memory, ROM Subsystem, RAM Subsystem

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

600

computer

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,

or

a

64-MB

DIMM. The

memory capacity

can

be

increased

up

to

160 MB.

The total amount of usable memory is less than the amount of memory installed because of ROM-to-RAM remapping and power management.

System Board 2-15