Memory

(Before you study this chapter, you may need to read chapter 18, Numbering systems.)

Bits

A "bit" is the smallest piece of data stored in your computer's memory. The value of a bit can be either 0 or 1. All data in your computer has a certain number of bits.

Bytes

A "byte" is 8 bits, and can have a value between 0 and 255 (or, in binary, between 0 and 11111111). A character, such as Q, takes up one byte of memory. This is because there are 256 different characters.

( If you don't fully understand bits and bytes, don't worry about it. )

How data is stored

Data is stored in RAM at a certain memory address, as explained in chapter 3 (Variables) . Each address takes up 1 byte of memory. Therefore, it can only have a value between 0 and 255.

A memory address (on a 32-bit computer) can be somewhere between 0 and 4,294,967,295. In hexadecimal, this is between 0 and FFFFFFFF.

Each memory address is divided into two parts: segments and offsets. See the figure below.

Segments and offsets

A memory address such as 12345678 (in hexadecimal) has a segment of 1234 and an offset of 5678.

A segment can have a value between 0 and 65535 (or between 0 and FFFF) . An offset can be within the same range.

You can find out a memory address of a piece of data by multiplying its segment by 65536 (or 10000, in hexadecimal) and then adding its offset to the result. In QBasic, you can get a variable's segment by using VARSEG and its offset by using VARPTR.

segment = VARSEG(x) offset = VARPTR(x)

' This prints the memory address of "x" (in decimal):

PRINT (segment * 65536) + offset