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Memory Abstractions

Internal Apparatus

Adventure pioneered the three-part

structure which became typical:

1. The prologue is the above-ground
   region of the game, played at ease,
   leading to the sense of foreboding
   and claustrophobia found in the
   upcoming bulk of the game.


2. The transition is the middle game,
   the passage from the mundane to
   pure fantasy.


3. The end game or master game pres-
   ents the final puzzle or challenge.
   Skip forward to 1986. The original
   Nintendo Entertainment System^7 was
   just being introduced. The Legend of
   Zelda would appear the following year.
   I’d never heard of Nintendo, but I’d
   played and solved Zork^8 in addition to
   Adventure.

Text games, to be sure, are not as

interesting as video games. They’re

deterministic. You only need to solve

the game once. But it’s 1986, and I’m

in the midst of a text-based adven-

ture, and about to deal with memory

management.

Cray Research was building main-

frame computers. There were so few

in existence that customers sent their

programmers to Cray Research to learn

how to program the thing. There were

no other options. The months-long

training sequence optionally included

the operating system internals.

Figure 2 is a listing of (part of ) the

operating system’s memory allocation

function, and there’s a possible bug in

the code. We can learn something from

that bug, even though the source code

is CRAY-1 assembly language!

Focus on the comments. They begin

with * in the left column.

Note the comment at line A0255.975:

Verify that the requested size is not

larger than the pool

7 Nintendo Entertainment System:

https://phpa.me/wikip-history-nintendo

8 Zork: https://en.wikipedia.org/wiki/Zork

Figure 1

Figure 2. Operating System Listing