By Tom R. Halfhill — originally published in Volume 1 – Issue 1 – June, 1983
Each month, COMPUTE!’s Gazette for Commodore will tackle some questions we are commonly asked by new VIC-20/Commodore 64 owners and by people shopping for their first home computer.
Q. After purchasing a Commodore 64, I am curious as to the differences in programming the VIC-20 versus the Commodore 64. Is the VIC-20 BASIC the same as the 64’s? If not, what changes must be made to run VIC-20 programs on the 64? I have seen several programs listed for the VIC-20, and have not read if they can be used on the 64 or not.
A. The Commodore 64 does indeed have the same BASIC programming language as the VIC-20. It is a version of the widely used Microsoft BASIC, originally written for Commodore by Microsoft, Inc. Most home computers use some version of Microsoft BASIC. To Commodore users, the version in the VIC-20 and 64 is known as Upgrade ROM, or sometimes, BASIC 2.0. Upgrade ROM derives its name from the fact that it is an upgraded version of the BASIC found in the original Commodore PET computer introduced in 1977. The BASIC is stored in a Read Only Memory (ROM) chip which was upgraded in later PETs. Commodore chose to equip the VIC-20 and 64 with this upgraded version. Some other Commodore computers have an even newer version, known as BASIC 4.0.
So what does all this mean to the VIC-20 and 64 programmer? Fundamentally, the BASICs are the same. But this does not mean that programs written for one computer will automatically run on the other.
The problem is that the VIC-20 and 64, though nearly identical in appearance, are very different computers inside. One major difference is their memories. Of course, the 64 comes with more than a dozen times as much memory as the standard VIC. But the differences go even deeper. The internal arrangement of the memory is not the same. For instance, the screen memory – an area of memory set aside for storing characters displayed on the screen – is not in the same place on both computers. This means programs which use screen memory will have to be adjusted, or they will not work.
Another difference is in the way the VIC and 64 create sounds. The 64 has an advanced synthesizer-on-a-chip which is much more flexible (and complicated) than the VIC’s tone generator.
Still another difference is in the two computers’ screen formats. The VIC can display only 22 characters across the screen, while the 64 displays 40. Programs written for one computer will not work, or at least will look very strange, if run on the other computer.
There are other, similar, differences. Translating programs between the two computers is basically a matter of tediously resolving these differences. It will be easier to convert VIC programs for the 64 than vice versa, since the 64 has special features not available on the VIC.
We intend to have continuing coverage of this subject in COMPUTE!’s Gazette for Commodore. Also, when we publish programs for the VIC and 64, whenever practical we will print a translated version for the other computer.
Q. Can the VIC-20 be upgraded to a Commodore 64? If so, does Commodore plan to make available such an upgrade?
A. The answer to both questions is a pretty certain “no.” Don’t underestimate the differences between the VIC-20 and Commodore 64. The two computers appear almost identical – sharing the same housing and keyboard – and some people mistakenly refer to the Commodore 64 as the “VIC-64.” But as explained above, the VIC and 64 have significant internal differences. “Upgrading” a VIC to a 64 could more accurately be described as “rebuilding.” It would probably cost more in parts and labor than what a new 64 sells for.
However, some upgrades for the VIC are theoretically possible. For instance, the 64’s synthesizer sound chip could be built into a plug-in cartridge for the VIC. Also, the microchip which is the VIC’s central “brain” is capable of addressing a total of 64K of memory, twice as much as the current maximum on the computer.
Commodore has hinted recently that an upgraded version of the VIC is at least a possibility. This might be something as simple as 16K standard memory instead of the current 5K. Whether it actually happens depends partly on the competitive situation in the low-end home computer market, partly on declining manufacturing costs, and partly on what Commodore perceives as gaps in its product line.