Re: Retrieving JPG and GIF file data in an AS/400 program

Bob Crothers wrote:
> 
> Rob,
> 
> Little/Big Endian refers to the byte ordering.
> 
> In the AS/400 world (Aka: Big Endian), integer data is stored with the high
> order bytes first and low order bytes last.  As you would expect.
> 
> In the Intel (and others) world, they use little endian.  Eg: the LOW order
> bytes come first followed by the high order bytes...in reverse order than
> you would expect.
> 
> The result is in the as/400 world, a integer (binary) 16 bit value of 1
> looks like hexadecimal x'0001' in memory/disk.  In the Intel or little
> endian world, the same data would be x'0100'.
> 
> These issues become very important when doing cross platform stuff.
> 
> Why is this done?  Beats me.  Has something to do with the hardware level
> and efficiency.  I just know this is the way the world is.
> 

I believe this can be traced back to the original 8 bit processors for
intel.  The first one I worked on was an 8008.  It was all direct coding
in octal.  As I recall to process two numbers you had to load the low
order bytes first and then use the carry flag on the high order bytes. 
So the little endian order made more sense.  All the intel processors
after that kept the same byte order (Z80, 8080, 8088, 8086, 80286,
etc.).   

John Hall 
Home Sales Co.
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