Archive for April, 2020

Intel 4004 μ-Computer (SIM4-01)

April 19, 2020

Some time ago, there was an Intel 4004-based singleboard computer for sale on ebay. The name of this computer was printed on the board: “Intel 4004 μ-Computer”. I did not buy it (also because the price was too high), but I never had heard about it, plus it was based on the first commercially available microprocessor, the Intel 4004. Now, the Intel 4004 is not only well known for its historical importance, but also that it was not really meant to be the heart of a small computer as it was designed to be used in a calculator. So what is this “mu-Computer” contraption?

Intel designed the 4004 as the CPU chip in its 4-chip family from 1971, the MCS-4. The other MCS-4 chips were the 4001 (masked-programmed) 256 bytes ROM, the (80 x 4 bit) 4002 RAM, and the 4003 shift register. The 4003 was meant as the basis to provide MCS-4-based systems output ports e.g. in order to control displays or other peripheral devices. The MCS-4 chips used a 4-bit data bus (although the 4004 supported 8 bit commands). The clock frequency of the 4004 was 500 – 740 kHz.

In 1971 Intel was mainly a RAM and ROM manufacturer who sold only components to their customers. (Mask-programmed) ROMs were ROMs whose content needed to be set during the actual manufacturing of the chip silicon, so a change in ROM contents needed several weeks until a new ROM with the new content was available. This was of course a problem for the software developers because they could change their software quickly, but then had to wait weeks until the new version could be used. Therefore, also in 1971 Intel announced a new product, the first EPROM. This was a ROM type whose content can be changed in a matter of minutes as it was stored in a re-writable manner on the chip (EPROMs are the chips with the glass window in the middle and often a sticker on top of that window). So, developers could program their system, create a new version of their software on their system, and when the software was stable, a traditional (and much cheaper) ROM could be produced without the need of many iterations.

Therefore, Intel felt the need to support developers using their MCS-4 products with first, a development system based on the MCS-4 that accepted either ROM or EPROM chips and second, with an EPROM programming device that allowed to load new content to an EPROM (an EPROM burner in today’s technology). The first development system is the 4004 μ-Computer. “mu” like the greek μ sign for “micro”. How did that device look like (that later on basically every CPU manufacturer would produce and sell for promoting their own design)?

The 4 large sockets on the top left corner can hold either a ROM or an EPROM chip each. The small chip on the bottom left corner is the 4004 CPU (tiny because of the 4 bit bus), and the 4 sockets to the right of it can hold a 4002 RAM chip each, giving it a whopping maximum of 160 bytes of writable memory. The other chips on the board are not really interesting (at least from my point of view). I read that the board actually has no 4003 chip on it, probably because there is no real standard design in a MCS-4 computer for it as this depends on what devices you want to connect. There are no recognizable interfaces on the board, just an edge connector of no recognisable standard at the bottom. So how do you connect something to this card? Meet the Intel MCB4 (Micro Computer Connector Board) chassis:

The chassis (the box on the bottom helds an 4004 mu-Computer on the front slot, and the second device, the EPROM burner on the back slot. It offers some switches, some lights, some interfaces and one (E?)PROM socket. You connect a TTY to the chassis, and voila: an entire microcomputer, ready to use.

Now, if you looked at the first picture and wondered where it said “mu-Computer”, well it doesn’t, it says “SIM4-01”. This is the (slightly) later name for the board. See, the problem was that Intel did feel that it was a component manufacturer, not a producer of computers, and that it should not be perceived (especially by its computer manufacturing customers) as such. Therefore, after some management thinking, this was not the 4004 micro-computer, this was the MCS-4 simulation device (SIM4-01), and you will find it much more often under that latter name. If you are interested in the history of the 4004 mu-Computer and especially the aspect of Intel shying away from being perceived as a computer manufacturer, I can wholeheartedly recommend the excellent article of Zbigniew Stachniak on exactly this topic (see [Stachniak] in the references).

The 4004 mu-Computer was probably the first computer with a 4004 CPU, the first microprocessor. Therefore, one can probably also call him the first microcomputer (if its definition requires a microprocessor). It (and its descendants like the twin brother SIM4-01 and the younger, healthier brother SIM4-02) can even be the only historic, commercially available, programmable computer with a 4004 CPU.

Technical Data

Manufacturer: Intel
Model: 4004 mu-Computer (a.k.a. SIM4-01)
CPU: Intel 4004
ROM: 4 sockets for 256 bytes Intel 4001 ROM, or 1701 or 1702 EPROM each
RAM: 4 sockets for Intel 4002 RAMs (80 x 4 bit = 40 bytes each)
Interfaces: 72-pin edge connector, allowing for 6 I/O ports (2 in and 4 out), and TTY
Released: 1971
Initial price: ???


The Value of a Computer over its Lifetime

April 13, 2020

I’m currently in the process of compiling a presentation on “Collecting Old Computers as a Hobby” for the upcoming VCFB 2020 event. I’m not sure whether it really fits in that presentation, but I made a highly speculative, subjective chart on, what I think, the value of a computer over its lifetime looks like. Here it is:


Let me explain. First, I differentiate the lifetime of a computer into 4 phases.

The “phase of usefulness” starts when the model comes onto the primary market, i.e. when it’s new. Obviously, the manufacturer thinks that it will be bought because it offers some benefit to the buyer. It is sold at the initial price (which typically will decrease over the time the model is offered by the manufacturer). I think it is not unreasonable to assume that the value of the computer, once bought, drops exponentially in this phase, especially when it it a state-of-the-art model. As it approaches the end of the usefulness phase, it typically drops to a more symbolic value that is basically determined by the minimum amount a seller is willing to accept in order for the entire transaction to make sense at all (i.e. compensating for the effort of the seller to offer, handle, and sell the thing. If the offered price would be any lower, it would not be worth the effort of the seller to do anything. If this computer model was bought originally by a company, it is most probably written off since some time anyway, to the company cannot put any value on it. The length of this phase depends probably on different factors, but maybe something like 10 years is not completely wrong for a computer. This phase transitions into

The “garbage phase“. The computer has no usefulness anymore, but it is not so old already that there are sentimental feelings connected to it. In this phase, the value is minimal and probably quite stable around the symbolic value I tried to establish in the last paragraph. Maybe in this phase it is not handled by the original owner, but by traders who specialize in surplus goods, making the price of the computer maybe even a tad lower because such traders are more efficient at low prices. I put a length of this phase also at around 10 years and try to substantiate that in the next paragraph, because the next phase is

The “sentimental phase“. This phase has a lot to do with the average age of a typical collector of a computer. Typically, they either had this computer model when they where young, or they were around when this model was fresh on the market. Since this phase probably 20 years or more has passed and they remember this time in retrospect with positive feelings (who does not remember his/her youth with joy? The music was much better than nowadays, the world was not that complicated and there was much less hatred and selfishness in the world). Also, being his his/her late 30s, 40s, and early 50s, things start to settle down for yourself. Often, there is less shortage of money, and less time needed to find a partner. For sure you don’t have a midlife crisis, but all this urge to buy a motorcyle… 🙂 Now, this is the time to feel young again with the dream machines of your youth, to fulfill unfilled dreams of owning cool stuff for a bargain. As a result, people start collecting computers. This process starts slowly, only a few people start collecting, but now the prices raise again. More and more people collect computers, maybe collecting becomes cool, and , with the raising prices, maybe even a good opportunity to invest money.

My theory is that the prices of a computer a collector wants to buy are:

  • not dependent on the initial price
  • dependent on a bunch of other factors, e.g.
    • how rare the model is
    • how many other collectors the model want
    • and, almost more importantly, what the buyer is willing to pay for a sentimental, or decorative, or conversation piece

I have also the impression (although I did not invest time into this to prove it) that these new values are clustered (and I put some estimation of how large these clusters are in the figure). Also, these price clusters increase over time as inflation and salaries increase over time. Finally, people think that the prices will go up forever and start thinking of them as investments (which will draw in also non-collectors that will act as investors).

This phase ends when the majority of the collectors starts getting so old, cool stuff from one’s youth is getting less important. This happens when no younger collectors replace the old ones, e.g. because the age of computers being cool stopped at some point. There are some areas where new collectors seem to continously “re-grow”, e.g. art and antiquities. There are other areas that flourished over many years, but suddenly came to a lack of collectors, e.g. stamps. My assumption is that, as computers became utilitarian in the 2000s instead of being fresh and not understood by parents, they aren’t as magical to millenials as they are to earlier generations (this is probably different to consoles and game-related computing, these will probably thrive much longer). If my prediction is correct, then prices at the end of this phase will drop dramatically as the market vanishes and the budget per collector gets much smaller.

It is also no clear to me what the next phase after the sentimental one is, and how this changes the prices for old computers.

In summary, here some conclusions:

  • most computers have their highest value when they are sold initially
  • the best phase to buy an old computer is the garbage phase (which is long gone for computers up to the year 2000)
  • do not buy old computers as a long-term investment

So, here you have it, my wild, highly speculative look into a crystal ball. What do you think?