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MOnSter 6502 - Prototype sized MOS 6502 Microprocessor

Updated 17 October 2019


The really exciting thing about retro computing is the interesting and occasionally zany maker projects people get up to. The MOnSter 6502 is a case in point. The legendary MOS 6502 microprocessor is one the great microcomputer chips of all time. It is one thing to reproduce the chip and a totally different experience to making an life-sized prototype on a motherboard. If you are not aware of the microcomputers that were built around the 6502 then you should make yourself aware of them.

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Why are we interested in the Monster 6502?

We find the Maker culture fascinating. It is a bunch of normal people doing extraordinary things that would have been considered pure science fiction only a few decades ago. Remember when your father used to tinker in the garage on his car? Well now the kids have grown up and they are doing their own creations. The Monstor 6502 is a project of this variety.

What is a microprocessor?

Before we delve into discussing the Monster 6502, it is worth starting at the beginning. Inside every computer there is a Central Processing Unit, or CPU. The CPU is a minature peice of circutry that processess information. All those 1s and 0s into other 0s and 1s. The CPU also handles in the input and output controls to get the information to where it needs to be. CPUs haven't changed in fucntion all that much since the dawn of the computing age. It's just that they have got smaller, faster, cheaper and ubquitous.

Believe it or not, the CPU isn't all that useful by itself. Over time, designers up more functionality and circitry on the chip so it has more capability on the single chip. Functionality like memory controllers, device controllers, maths coprocessors can be added onto the same chip. While this increaseses the cost of fabricating the processor, it decreases the overall cost to manufacture the computer motherboard becuase the number of parts on the motherboard decrease. The multi-function CPU circuits are called microprocessors.

In very basic terms, microprocessors have been getting more advanced circuit technology, leading to these chips have more capacity to process data. Instead of processing one data bit (0 or 1) at a time, the microprocessor can handle groups of 0s and 1s, known as data objects. These data objects have increase over time from 4-bit, 8-bit, 16-bit, 32-bit and now commonly 64-bits in size. Of course, users do not see how many bits your computer is using because it has become irrelevant to the normal computer use nowadays. Early on though, the processing capacity was very limited. The smaller processors could only handle small numbers, meaning that they could only address a small amount of memory and had a limited number they could count up to. The largest 8-bit whole number that can be counted in a measly 255 (counting from 0 to 255, or 256 numbers). A 16-bit computer can count whole numbers up to 65535. That is one reason why many microcomputers back in the day came with 64kb of memory. As always, there are ways to get around this limitation, like with memore controllers and page mapping, but these come with performance and price penalties.

Common microprocessors today use 64-bit technology. The most common examples we can find in the marketplace are the Intel Core i5 processors (wayback, AMD Ryzen processors (wayback), and the Qualcomm Spandragon processors (wayback). As you can see, things have certainly got more complicated than just discussing the data object size that a microprocessor can handle. It is also obvious that the current market is working in the 64-bit bit space and trying to solve other problems, rather than jumping to the next obvious step, a 128-bit solution.

Why make the Monster 6502?

The best way to learn about something and become intimate with it is to sketch up and build one yourself. Engineering is full on compromises. Going through the design process and working through the design assumptions, choices and compromises; then progressing into frabrication and assembly will give the Maker the best feeling for what it was like to develop one of the most successful micrprocessors ever made.

The project is hosted on the MOnSter 6502 website. The site is a bit sparse on image and video but the description is approachable for the novice and it gives an open perspective of the project itself.

Fun Fact: the lifesize version of the chip is slower than the original 1970s original.

Our favourite microcomputers using the MOS 6502 processor family

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