OLD-COMPUTERS.COM : The Museum

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It uses material from the Wikipedia article "Galaksija" (see this entry for uptodate text)
Mainly written by Aleksandar Šušnjar

GALAKSIJA

The Galaksija (pronounced Galaxiya, meaning Galaxy) was originally a build-it-yourself computer designed by Voja Antonic. It was featured in the special edition Racunari u vašoj kuci (Computers in your home) of a popular science magazine of the same name, published late December 1983 in Yugoslavia. Kits were available but not required as it could be built entirely out of standard off-the-shelf parts. It was later also available in complete form.

HOW IT BECAME

At the time various laws in Yugoslavia prevented importing computers into the country. At the same time, even the cheapest computers available on the west were nearing average monthly salaries. This meant that, regardless of interest, only a relative minority of people owned one - mostly ZX Spectrum or Commodore 64.

According to his own words, some time in 1983, Voja Antonic, while vacationing in hotel Teuta in Risan he was reading the application handbook for CDP1802 CPU and stumbled upon CPU-assisted video generation. Since CDP1802 was very primitive, he decided that Z80 can do it as well.

Before he returned home, to Belgrade, he already had the conceptual diagrams of a computer that uses software to generate video picture. Although significantly reduces computer peformance it also simplifies the hardware and reduces its cost.

Next step was to find the magazine to publish the diagrams in. Obvious choice was SAM Magazine published in Zagreb, but due to prior bad experiences he decided otherwise.

Popular science magazine Galaksija appeared unrelated but, after he heard that they were working on a special issue dedicated to computers he found his answer. He proposed publishing entire do-it-yourself diagrams, instructions, etc to the author of the issue, Dejan Ristanovic. Everything made its way into the special issue called Racunari u vašoj kuci. It was released late December 1983, although it was dated January 1984.

They tried to guess the number of Galaksijas that will be built this way. Their estimates ranged from a hundred to a thousand (a number that sounded so optimistic it provoked laughter). Actual number built by "do-it-yourselfers" - was around 8000! This number may in reallity be greater if people who did not purchase any kits (including PCB and *ROMs) are accounted for.

IMPACT

Galaksija was almost not comparable by any measure of features to the commercially available computers at the time. However it may sound - that was not important. What it did is sparked the minds of many people. Many (incl. the author of this text) have learned how computers actually work by looking at Galaksija's schematic diagrams and Voja's great descriptions. It was a great learning tool. Making a computer yourself boosts confidence and brings on the challenges of making the best out of it.

Computer's popularity because significant enough that it became commercially available. Many educational institutions were given some. Although many of them were not ready for the experience, many others used it as a great tool to teach computer science (computer architecture and programming) even in elementary schools (in 1984!).

BASIC in 4 KB ROM

Galaksija has a BASIC interpreter that was originally based on Microsoft Level 1 BASIC. However, after extensive modifications to include video generation code (as the CPU was a major participant to reduce the cost of hardware) and improve the language, what remained from the original is said to be mainly flow-control and floating point code.

ROM A BASIC keywords :

ARR$(n) - (need details here)

BYTE serves as PEEK when used as a function (e.g. PRINT BYTE(11123)) and POKE when used as a command (e.g. BYTE 11123,123).

CALL n (e.g. CALL 100+4*X)

CHR$(n) converts an ASCII numeric code into a corresponding character (string)

DOT x,y draws (command) or inspects (function) a pixel at given coordinates (0<=x<=63, 0<=y<=47).

DOT * displays the clock or time controlled by content of Y$ variable.

EDIT n causes specified program line to be edited

ELSE standard part of IF-ELSE construct (Galaksija did not use THEN)

EQ - (need details here)

FOR standard FOR loop

GOTO standard GOTO command

HOME equivalent of standard BASIC CLS command - clears the screen

HOME n protects n characters from the top of the screen from being scrolled away

IF standard part of IF-ELSE construct (Galaksija did not use THEN)

INT(n) a function that returns the greatest integer value equal to or lesser than n

KEY(n) test whether a particular keyboard key is pressed

LIST lists the program. Optional numeric argument specifies the first line number to begin listing with.

MEM returns memory consuption data (need details here)

NEW clears the current BASIC program

NEW n - (need details here)

NEXT - standard terminator of FOR loop

OLD - loads a program from tape

OLD n (need details here)

RND - function (takes no arguments) that returns a random number between 0 and 1.

RUN - runs (executes) BASIC program. Optional numeric argument specifies the line number to begin execution with.

SAVE - saves a program to tape. Optional two arguments specify memory range to be saved (need details here).

STEP - standard part of FOR loop

STOP stops execution of BASIC program

UNDOT x,y "undraws" (resets) at specified coordinates (see DOT)

! - begins a comment (equivalent of standard BASIC REM command.

& - prefix for HEX numbers

Approximatelly 70% of CPU time was used just to generate video, which made Galaksija relatively slow in normal operation. This was unacceptable while saving or loading data from the tape so video generation was disabled during tape operations. There is also a way to disable (and re-enable) video generation from BASIC when "fast computation" is required. With video disabled, built-in BASIC interpeter was in many instances able to outperform interpreters of other home computers of the time.

Galaksija's BASIC has slightly different names for standard commands (e.g. BYTE instead of PEEK and POKE, OLD instead of LOAD, etc). This was done to assure that most commands begin with different letters. Not only this helps the intepreter in recognizing the command but also allowed all commands to be abbreviated to a single letter followed by a dot (e.g. "P." instead of "PRINT") and, thus, take less memory for the same program, albeit with reduced readability.

Galaksija's intepreter can report only a few error messages - notably "WHAT?" and "HOW?". This made more ROM space available to code.

"READY" prompt (bytes in ROM representing it) is also used as code in video generation routine.

To simplify "do-it-yourself" building and reduce cost, the Printed circuit board was designed as single-layer (single-side) board. This resulted in a relatively complicated design requiring many components-side connections to be made using wires.

Among standard ways of distributing software, Galaksija programs used to be broadcasted over FM Radio "Beograd 202" in a show Ventilator 202, hosted by Zoran Modli. At 280 bit/s, a mere 2 KiB program would take a whole minute of characteristic noise that only computer enthusiasts enjoyed.