Type of Data Storage

Storage Background:
Computer memory, or storage, is divided into groupings called bytes. This page runs through all the types of storage used in assembler.

Each byte of storage is uniquely addressable:


 * Smallest address = 0


 * Largest address = 00FFFFFF or 7FFFFFFFF


 * or FFFFFFFF:FFFFFFFF depending on hardware/software

History:
The original s/360 series machines only had real memory, and the maximum address used was 00FFFFFF or 16,777,215 bytes of storage.

The XA series computers had virtual storage, and the maximum address used was 7FFFFFFF or 2,147,483,647 bytes of storage

For z series computers the maximum address used is FFFFFFFF:FFFFFFFF or 18,446,744,073,709,551,615 bytes of storage

Address 16,777,216 is known as the “line” separating 24-bit addresses from 31-bit addresses.Storage below the line is addressable by 24 bits; storage above the line needs 31 bits. Address 2,147,483,648 is know as the “bar” separating 31-bit addresses from 64 bit addresses