54

R&D stuff isn't manufactured (at first). It's usually partially constructed, ripped up, and redone, multiple times, with long testing and debug cycles in between, all the while with payroll running up the tab. Tons (literally) of fried or used components and partial assemblies can go into the junk bin. The specifications then often evolve with the ...


37

there some particular design theory or constraint that made a 32-bit word size attractive for IBM to migrate to? It all comes down to the most basic data type, addressing constrains and, less important, reuse of existing memory technology. The byte size had to be a multiple of 4, as needed to accommodate BCD numbers without wasting space. So 8 was chosen ...


37

The early Apple Macintosh computers (original Mac, Mac 512K, Mac Plus) all came with a "Programmer's Switch" installed on the side. Yes and no. While the switch was there, it was on the inside, so, not really accessible. Only after being 'enhanced' with the so called 'Programmers Key Aid', a snap on after market piece of plastic, griping into the ...


24

The "programmer's switch" is more technically known as the NMI (Non Maskable Interrupt) switch. It is mapped to a priority 7 interrupt on the 68K CPU, which means it is capable of interrupting anything besides another priority 7 event. When pressed, the CPU saves all its state on the stack, switches to privileged mode, then looks at the interrupt ...


24

So what was the other $478,000 spent on? Paying people to design and build it would have been a fairly big component. People often underestimate the cost of labour, particularly if it is their own time. Also looking at the photos of it on wikipedia, there were a lot of components besides valves. There were racks and other cabinets and what looks like a ...


20

One of the biggest factors is that when you have a machine that requires 5,000,000 successful solder joints to function properly, you need to make sure that all of your solder joints are really really good. If 1 in 10,000 of your solder joints is subtly bad, that means that the first time you try to put everything together you will have 5000 bad solders and ...


19

Without detailed documentation on the PDP-8 design process, we cannot say for sure. I suspect that while they may have briefly considered it, it was never a serious prospect. The PDP-8 is just the PDP-5 redesigned electronically. The PDP-5 was introduced in 1963 as an even-more-reduced version of a computer compared to the PDP-1 and PDP-4. The PDP-1/4 did ...


10

Wire Wrap as used in computers is simply a later development then the ENIAC or vacuum tubes in general (*1). The Keller tools were first marketed in 1953 and it took a few more years until they made their way from telephone to computers. IBM might have been the first, around 1960, a bit before the /360 came which, used it a all over. *1 - In contrast, PCBs ...


10

It's simply how the 8086 works. it's a straight 16 bit CPU, isn't it? The CPU sees memory not as an 20 bit address space, only the BIU does (*1) when generating an access, but a 16 bit segment number, in CS, and a 16 bit PC in IP. The BIU uses a result derivated from CS and IP to access memory. When fetching instructions (without an MMU like in the 286) the ...


7

Here's a video about manufacturing UNIVAC 1108 (circa 1965, so a bit later but still illuminating). Notice how much is done by hand, even things like winding coils. According to the University of Minnesota the UNIVAC division employed about 10,000 people. Price list for some UNIVAC 1104 components (long page of text, search for "UNIVAC 1004 PRICE LIST&...


7

Very briefly: The way harddisks are addressed changed over time. Originally, you'd specify cylinder/head/sector (CHS), then it switched to logical block addresses (LBA), and the commands for those went through various versions with an increasing number of bits. As you can read on Wikipedia, LBA first used 22 bits, then 28, then 48. So you need to distinguish ...


7

I'm going to say no. The PDP-8 was chiefly designed for compatibility with the PDP-5, and this machine also had no hardware stack. There is not enough room in the instruction space to add push and pop instructions either.


6

Well, depends on the definition of dual port. After all, all 9918ff based machines can as well be classified as dual ported. Similar PC graphic cards, like VGA. Beside that, the most most important reason was No need to do so. Early 8 bit CPUs were not only slow enough (compared to RAM) to allow interleaved video and CPU access on a fixed schedule, it as ...


6

One small reason is that you can access memory as a bit array without needing to divide (or do a modulo). Just use the bottom N bits for the byte or word or data cache line position or shift, and the rest of the bits left over as a memory address offset. Which can be done in hardware for free if needed.


5

Worthy of mention is the rise of the microprocessor- notably the 4004 which was designed for mostly numerical operation in calculators. Whether the step to 8 bit architecture was inevitable is open to debate, but once memory ICs started being produced in 8-bit forms, it would be difficult to justify anything other than 16-bit as the next step. Looking at ...


5

That BIOS screen clearly says that it detects the drive as roughly 8 GB. The parameters say 16383/16/63 as so this BIOS cannot detect or provide the extended disk services that would allow the drive to be used beyond the 16383 cylinders, or the 8GB limit. It does not matter if another program can detect the size properly by communicating with the drive ...


5

But I'm used to a flip-flop being made of six transistors, which suggests it would need six triodes, Not really, a basic flip flop does not need 6 transistors. maybe there's a mix up with RAM cells? Two will do it quite fine (*1,*2). Similar the two triodes of a 6SN7 is all what's needed - well, plus two rather equal resistors between them and another two ...


4

Was it ever possible to take an actual existing punch card reader, and hack a connection to hook it up to a computer? No, why? The existing tabulating machine was all about parallel processing. Or was it the case that yes the existing cards could be reused, but to use them with computers required designing and building all new equipment? No. Of course not....


4

Comments have already covered that the CPU manual should answer all your questions, but above and beyond that, immediate observations: ld (nn), bc is encoded as ed43 so that's two reads; the actual address, 0x1000 is also two bytes long, so that's another two reads; bc is two bytes long, so that must be two writes. In total that's six memory accesses, from ...


3

The IBM PS/2 model 30 (and it's variant, model 25) use 64K of VRAM in their MCGA video system. They manage to display the 256-color VGA graphics mode (requiring around 12.6MB/s streaming to the monitor) with an 8-bit data bus, whereas the VGA card requires a 32-bit data bus with its single-ported data RAM to provide enough bandwidth. The video RAM chips are ...


3

Not sure I would trust 30 gauge wire wrap wire insulation with vacuum tube plate voltage. The cross-talk at the higher voltages plus digital edge speeds would also be far worse.


2

A conventional flip flop requires the following: Two inverting switching elements that will strongly pull their output in the direction opposite what's required to turn them on. Two elements that can weakly pull the output of whichever switching element isn't on in the opposite direction. Two elements that, in response to external stimuli, can pull those ...


1

Given packaged component costs at the time, for a given performance target, it was cheaper to time division multiplex either a wider or faster memory bus than to procure dual ported chips (much lower volume and/or higher pin count packages, synchronization circuit costs. etc). Pins were not free.


1

This is how my emulator stores this instruction: ---------------------------------------------------------------------- |opc T0 T1 MC1 MC2 MC3 MC4 MC5 MC6 MC7 mnem | |--------------------------------------------------------------------| |ED43L1H1 20 00 M1R 4 M1R 4 MRD 3 MRD 3 MWR 3 MWR 3 ... 0 LD (U16),BC| ----------------------------...


1

Reading a single punched card is not very difficult. You just need enough photodiodes or spring pins to sense all the rows in one column, and a mechanism to advance the card precisely from one column to the next. The tricky part is handling many cards in sequence, and keeping them in sequence in the output tray for later reuse. IBM had already solved these ...


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