One of the many reasons why Linux is such a popular operating system is that it can give new life to older computers. Instead of chucking an aging desktop into the trash, you can install a lightweight Linux distribution on it, and it will run like a champ.
But what if that old computer is from 1971? Would it be possible to install an operating system that was invented almost 30 years later? Dmitry Grinberg has shown it is possible to do just that.
The chip in question is a 4-bit Intel 4004 processor, which was the first commercially produced microprocessor and includes only 2,600 transistors and can handle a very limited number of operations. The CPU doesn’t support hardware interrupts, which means multitasking isn’t exactly an option.
Of the Intel 4004 chip, Grinberg said, “…the 4004 does not perform any memory operations – the other chips on the bus are expected to decode them and perform them if they are selected. The ‘selection’ is made of a few parts. First is the CM-ROM line needs to indicate that this ROM bank is active during bus phase A3 (for code read) or X2 (for I/O ops).” He continues, “In the 4004, there is only one ROM back, so this is always the case. The 4040 has two CM-ROM lines and thus one bank may be not selected. The second part of ‘selection’ is whether the current chip in the bank is selected. This is determined from the last SRC instruction performed while this bank was selected. The chip thus addressed remembers this until another SRC instruction is observed while this bank is selected.”
Grinberg had to lean heavily into emulation and overclock the CPU to a 790 kHz clock speed. Once he had it running, at it took 9 days to boot the Linux kernel on the Intel 4004 CPU. He was eventually able to get the boot time down to 4.76 days.
You can watch a demo video of the boot process here.
