Section 2 - Commodore Computers

136 COMPUTEt tv1oy, 1982. Issue 24
136 COMPUTE) May. 1982. Issue 24
There are times when you will write a program that is so lmge large that it will need ev",)' every last meIlZ01)' memory cell in your
com/mler, computer. This (I,rtiele article shows several ways to Teduce reduce the size of yourIJ1'0!5"a.ms, programs. In general, geneml, thl'sl' these techniques a-/JI)I), apply 10 to
WI)' any computer rOIllI}//II''- using /lsillg BASIC, nol not just to the Ihe VIC-20,
VIC-20.
Putting The Squeeze
Putting The Squeeze
On Your VIC20: Getting The Most
Out Of 5000 Bytes
Out Of 5000 Bytes
Stanley M M. Berlin
Dallas,1X
IX
Five-thousand of almost anything seems like a lot;
a Christmas bonus of $5000 would make anyone
happy; 5000 jell y beans wo uld be more than even
happy; 5000jelly beans would be more than even
our Presidelll President could eat; 5000 days is over fourteen
years. However, there are otherr circumstances
when a quantity of five-thousand really is not so
when a quantity of fi ve-thousa nd really is not so
much, much. Five-thousand raindrops would probably go
unnoticed, unnoticed. The time when five-thousand is a reallyy
small quantity is when you are writing a program
and have onlyy five-thousand bytes (memory locations)
in which to do the job!
I remember working twenty years ago with a
4000 character IBM 1401I Computer and feeling
confident that if I had only another twenty-five
memory locations I would be able to complete the
program. program, Times have changed during the last
twenty years and there are many programmers
who now work with virtual memol)' memory systems. systems, [WheTe [Where the
computer can use disk memory as if il it weTe were RAM -— Ed.] Ed.}
where there is no such problem as being constrained
by the amount of memory, memory. With technology moving
as fast as it is, persons working on small microcomputers
probably y will not have to wait twenty
years for a virtual memory-like system. When that
tilne time arrives, people will not have to write articles
like this one. However, today, if you are writing
programs for the Commodore VIC-20 you will
have to li ve with the constraint of having only
have to live with the constraint of having only
5,000 bytes worth of memory in which to do your
work.
Anyone who has done any serious programming
Anyone who has done any serious programming
for the VIC20V I knows that it does not take many
BASIC statements before youu get that dreaded
"OUT OF MEMORY" message. Of course, the
VIC20 is nice enough to let you know when you
turn it on that by the time it gets through allocating
506 bytes for the video mapping, and another 506
bytes for color mapping on the screen, and reserves
memory space for such other things such as tape
cassette buffers, you have onlyy 3583 bytes of memory
in which to store your program.
So, there you are busily entering your new
BASIC program and VIC sends you the "OUT OF
MEMORY" message. What are your options? You
cann resign yourself to the factt that, no matter what
you do, the program will never fit into memory
and abandon your project. Surely, no programmer
worth his or her salt would exercise this option!
Another option is to run out and purchase a memory
expansion unit. unil. This is not too bad a solution
except, at the time this is being written, there is no
such item available. Even if there were, it is surely a
costly solution. The last option is to roll up your
sleeves and dig into yourr program with a finely
honed scalpel to perform surgery onn it. That is
certainly the most challenging option, and it is the
certainly the most challenging option, and it is the
purpose of this articlee to pass on a few points to
help you in your efforts.
The items discussed will be from a BASIC
programmer's point of view. Technical system
information will be avoided except when it is necessary
for a clear understanding of the issue. issue, Although
these suggestions are aimed at the VIC20
owner and the VIC20 is the computer used to
validate the data, much of the information is pertinent
to other computers using Microsoft BASIC.
One last point prior to moving to the meat of
this article; many of the suggestions presented
here are a tradeoff between good program docu­
here are a tradeoff between good program docu
mentation and the amount of memory used. Remark
(REM) statements li berall y scattered through­
mark (REM) statements liberally scattered through
out a program provide the roadmap when you are