Z/OS --- Why so different?

Data Sets        vs        Files
Manually Allocated        Automatically
Flat Directory            Hierarchy
Named Partitions          Block at a time
All due to Memory

Simplest  S/360  8KB    Simplest PDP-11 for Unix 28 KW = 56 KB
             >>>>BIG DIFFERENCE<<<<<

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Kestrel-2

 111  Lookup Tables and Variables
1535  Framebuffer
2048  Font
 786  Cursor
 564  TTY
1916  Keyboard
 716  Command-Line Interface (CLI)
2410  Forth implementation

Total: 10086 bytes
  RAM: 16384 bytes total
 Left:  6298 bytes