AOH :: VMEXPLAN.TXT|
The Paging Game: IBM's attempt to explain virtual memory in nontechnical terms
The Paging Game
The following is a technical update to IBM's explaination of how virtual
memory works. It was written by Jeff Berryman of the University of British
Columbia and distributed at a share meeting shortly after IBM announced
virtual memory for the 370 series.
1.) Each player gets several million 'things'.
2.) 'Things' are kept in 'crates' that hold 4096 'things' apiece.
'Things' in the same 'crate' are called 'crate-mates'.
3.) 'Crates' are stored either in the 'workshop' or the 'warehouse'.
The workshop is almost always too small to hold all the crates.
4.) There is only one workshop, but there may be many warehouses.
Everybody shares these.
5.) To identify things, each thing has its own 'thing number'.
6.) What you do with a thing is to 'zark' it. Everybody takes turns
7.) You can only 'zark' your things or shared things, not anyone else's.
8.) Things can only be 'zarked' when they are in the workshop.
9.) Only the 'Thing King' knows whether a thing is in the workshop or
10.) The longer the things in a crate go without being zarked, the
grubbier the crate is said to become.
11.) The way you get things is to ask the 'Thing King'. He only gives
out things in multiples of 4096 (that is, 'crates'). This is to keep the
royal overhead down.
12.) The way you zark a thing is to give its thing number. If you give
the number of a thing that happens to be in the workshop, it gets zarked
right away. If it is in a warehouse, the Thing King packs the crate containing
your thing into the workshop. If there is no room in the workshop, he first
find the grubbiest crate in the workshop (irregardless of whether it is yours
or someone else's) and packs it off (along with its crate-mates) to a
warehouse. In its place he puts the crate containing your thing. Your thing
then gets zarked, and you never knew that it wasn't in the workshop all along.
13.) Each player's stock of things has the same thing numbers (to the
players) as everyone else's. The Thing King always knows who owns what thing,
and whose turn it is to zark. Thus, one player can never accidentally zark
another player's things, even though they may have the same thing numbers.
The Paging Game..... NOTES:
A) Traditionally, the Thing King sits at a large, segmented table,
and is attended by pages (the so-called 'table pages') whose job it is to
help the Thing King remember where all the things are and to whom they
B) One consequence of rule # 13 is that everyone's thing numbers
will be the similar from game to game, regardless of the number of players.
C) The Thing King has a few things of his own, some of which get
grubbier, just as player's things do, and so move back and forth between the
workshop and the warehouse. Other things are used too often to get grubby, or
are just to heavy to move.
D) With the given set of rules, Oft-zarked things tend to get kept
mostly in the workshop, while little-zarked things stay mostly out in the
warehouse. This is efficient stock control.
E) Sometimes even the warehouses get full. The Thing King then has to
start piling crates upon the dump out back. This makes the game slower because
it takes a long time to get thing off the dump when they are needed in the
workshop. In this case, the Thing King selects the grubbiest crates he can
find in the warehouses and sends them to the dump in his spare time, thus
keeping the warehouses from getting too full. This also means that the
least-often zarked things end up on the dump, so the Thing King won't have to
get things from the dump so often. This speeds up the game when there are a lot
of players and the warehouses are getting full.
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