2018年3月7日 · The PDP-8/S, which arrived shortly after the original PDP-8, was in this category; however, because it used a serial arithmetic unit, it was slow and of limited popularity. The PDP-8/L, a computer using the same technology as the PDP-8/I, but with fewer available options, also had its logic behind the front panel.

2018年3月2日 · The PDP-8 designers wanted memory reference instructions (MRI) like TAD to be able to address zero-page, indirect, current-page, and zero-page-indirect memory references, which requires 2 bits in the instruction word: 00, 10, 01, and 11, respectively. That leaves 7 bits for MRI instructions, which gives the PDP-8 page size of 2⁷ = 128 words.

2016年10月20日 · The PDP-8 designers clearly had some foresight. Notice that multi-word addition uses RAL to get the carry into the accumulator and clear the link bit. I can't see how that trick can be applied to subtraction due to the need to complement the accumulator.

2014年5月31日 · "The PDP-8's magnetic core memory required write after read since the read operation was destructive and zeroed the read memory location." Very true; I believe this was true of all practical core memory, since writing a bit to a known state was the only practical way to read it.

2024年1月12日 · This answer is written from information sourced from PDP-8/E & PDP-8/M & PDP-8/F Maintenance Volume 1 (PDF warning). Here is a description of the datapath allowing the program counter to be incremented on the PDP-8/E, this is figure 3-2 in the book):

2024年1月12日 · The possibility of faulty or malicious code freezing the machine was common in those days, even for machines much more complicated than the PDP-8. Except for the rare specialized machines designed specifically for time sharing, nobody worried about needing occasional operator intervention to get the machine back on track.

2024年1月12日 · The PDP-8 was a popular 12-bit minicomputer of the late sixties. It used word addressing, so that it always dealt in 12-bit words, of which it could address 4096 with a full bank of core memory. In ...

2024年2月4日 · The PDP-8 had only a single user-accessible register, AC, besides the program counter, and so all operations using more than one data value had to take the second value from memory. Oral Histories Chuck Peddle worked on the development of the 6800 microprocessor at Motorola before he (rather more famously) went on to design the 6502 (which used ...

2024年1月10日 · I'm trying to find a single clear statement of the limits to the numbers represented in the PDP-8's three-word format. I found the original documents on this, but they are, ahem, not exactly forthright with this information. Page 3.10 shows the format with the exponent in the first word and the mantissa in the next two, but the exact format of ...

2025年2月2日 · All the PDP-8 I know have magnetic core, and you can see in the OS/8 manual that the manual authors also made the assumption "it's magnetic core, and keeps the value". If you have any information about existing installations with semiconductor memory, then the next question would be what other periphery they were using, and if they were using ...