Atari XL User Manual

CHAPTER 10
MEMORY MANAGEME'NT
The memory of a computer is built up from a large
number of storage units, each of which can hold one
number. Each storage unit is called a memory
location, and each location has a unique reference
number called its address. In a microcomputer like
the Atari XL, each memory location can hold an
eight-bit binary number, which can have a value
between 0 and 255. Larger numbers need more
than one location. (If you are not sure about binary
numbers, they are explained in Appendix 4.) Eight
bits of storage are called a byte in computer jargon,
so the memory locations of the XL hold one byte of
data each.
The microprocessor used in the XL, the 6502, is
able to make use of 65535 memory locations (65535
is 2
16
,
or 64k). Not all of this can be used for your
BASIC programs (the amount available depends on
which model XL you have), some of it is reserved
for use by the computer. The arrangement of
memory on the XL is shown in Appendix 13.
There are two types of memory used in a computer.
Random access memory, or RAM, is used to store
data, and its contents can be changed as the data
changes. Read only memory, or ROM, cannot be
altered and is used to store the programs the
computer needs to work at all; the BASIC
interpreter for example.
There are two BASIC commands, PEEK and
POKE, which are used to look at individual
memory locations. PEEK finds out the contents of
a location, and POKE writes a new number into
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Atari XL Specifications

General

Brand	Atari
Model	XL
Category	Desktop
Language	English