LITTLE ENDIAN vs BIG ENDIAN

"Little Endian" means that the low-order byte of the number is stored in memory at the lowest address, and the high-order byte at the highest address. (The little end comes first.)

For example, a 4 byte LongInt

    Byte3 Byte2 Byte1 Byte0

will be arranged in memory as follows:
   
Base Address+0   Byte0
   
Base Address+1   Byte1
   
Base Address+2   Byte2
   
Base Address+3   Byte3

Intel processors (those used in PC's) use "Little Endian" byte order.
"Big Endian" means that the high-order byte of the number is stored in memory at the lowest address, and the low-order byte at the highest address. (The big end comes first.)

Our LongInt, would then be stored as:
   
Base Address+0   Byte3
   
Base Address+1   Byte2
   
Base Address+2   Byte1
   
Base Address+3   Byte0

Motorola processors (those used in Mac's) use "Big Endian" byte order.

In "Little Endian" form, assembly language instructions for picking up a 1, 2, 4, or longer byte number proceed in exactly the same way for all formats: first pick up the lowest order byte at offset 0.

      Also, because of the 1:1 relationship between address offset and byte number (offset 0 is byte 0), multiple precision math routines are correspondingly easy to write.

In "Big Endian" form, by having the high-order byte come first, you can always test whether the number is positive or negative by looking at the byte at offset zero.
You don't have to know how long the number is, nor do you have to skip over any bytes to find the byte containing the sign information. The numbers are also stored in the order in which they are printed out, so binary to decimal routines are particularly efficient.

Common file formats and their endian order are as follows:
Adobe Photoshop -- Big Endian
BMP (Windows and OS/2 Bitmaps) -- Little Endian
DXF (AutoCad) -- Variable
GIF -- Little Endian
IMG (GEM Raster) -- Big Endian
JPEG -- Big Endian
FLI (Autodesk Animator) -- Little Endian
MacPaint -- Big Endian
PCX (PC Paintbrush) -- Little Endian