There are two things that keep me from expanding my collection of old computers: the cost and the space needed to store them. I have an old original TRS-80 and an old serial station (see video below). However, she abandons Data General's equipment and loses her old 1802 COSMAC Elf due to flooding. There have been many copies of older computers with varying degrees of accuracy, and they tend to be cheaper and smaller than the originals. I have an Altair replica, an Elf replica and a KIM-1 replica.
However, the cost and expense of real and replicas is hard to justify. The situation is even worse with really large machines, some of which require special power or cooling and are difficult to maintain. Another option, of course, is software emulation. Options like SIMH and Hercules work well, but they aren't always graphic and require a lot of work to set up a machine to play for hours or show a student how it was done in the good old days.
On the other hand, there are some older PC emulators that run right in your browser. No software to install, no hardware to set up, and a lot of it is graphics related. I know a lot of people don't want to post their work on a "cloud service", but I'm willing to risk a 30-line BASIC program guessing your number.
- PC/OSI are actually two different emulators, one for the IBM PC (which I can hardly call an old PC) and the other for the Ohio Scientific Challenger 1P. The site has many ready-made demos (including Windows 1.0) and you can also set up your own. Or maybe you prefer to play Wolfenstein and other games.
- Mac – If you don't like Windows, you might like Mac OS 7.
- Amiga. The Amiga had many features ahead of its time and you can try the Amiga 500 here.
- I still have the TRS-80 – Model III, but you can play VR in your browser.
- COSMAC Elf – The COSMAC Elf was the first computer I personally owned and this site contains a very detailed graphical version of the system along with some extras.
- KIM-1 was a very useful single computer that deployed the KIM 6502. This version of the browser gives you the feel of an old hobbyist computer.
- Altair – You need Java, but this emulator allows you to experience a computer that can start the home and hobby computer market.
- PDP/11 – Before Linux, there was Unix. This page allows you to run Unix 6 on a virtual PDP/11. The sixth version is so old that you should know that the cd command didn't exist yet (try chdir). Use the # key to go back and the @ key to delete a line (imagine you are using a vulture typewriter). If you are tired of capital letters, read the link on the site.
- EDSAC – Dr. Wilkes' EDSAC was one of the first modern computers to actually work. His team at Cambridge developed many of the approaches we take for granted today. This is a rare machine that can be programmed and you can refer to your computer emulator manual for more on how to program it.
- ENIAC. If you're having trouble programming EDSAC, try this (but you'll need a Java-enabled browser).
I'm sure there are others, but this is enough to get you started and I'm sure others will pick up on the comments. If you want to evaluate the difference between loading a web page and loading it on a real device, you can compare a PDP/11 recording with a real recording. There are also sites to connect to real old hardware, which can be the best of both worlds. For another crossover (modern simulator and old serial station) you can watch my video below where I try to save the galaxy from the Klingons.