71

TL;DR: It's the pipeline. The 80486 contains parallel operating stages for decoding, operand fetch, execution and write back. So while an ADD reg,reg does take 3 clocks to perform, as it did in the original 8086, its execution overlaps with the previous/next operation, so the CPU can crank out one ADD reg,reg per clock. The Long Read (Caveat, there's a whole ...


61

Having the display vertical reduces the width of the cabinet. This means that a game machine can be fitted into a smaller space in a pub/bar, or in an amusement arcade where machines are in rows you can get more machines (potentially a third more) into the same space. One-third more machines means one-third more revenue. The orientation may also have been ...


49

For the simple reason that until relatively recently, it was very difficult to make a rewritable optical medium, but it was easy to make a rewritable magnetic medium. Magnetic tape as a recording medium has been a practical technology since the late 1930s, predating the digital computer. For comparison, CD-RW was introduced only in 1997, more than a decade ...


46

After some more research, I believe I've stumbled across the real answer: The VIC-II and SID used a larger process node size because Commodore's fabrication line circa 1981 was uniquely positioned produce chips at that size at effectively no production cost whatsoever. Based on what I've read, here's my best guess at what Commodore's fabrication situation ...


45

When did computers stop checking memory on boot? Never. I remember my old 8088 used to do this (640K OK) but can't remember seeing anything like this since. Does this still happen and it's just not visible? Exactly. And it has been simplified and speed up as well. But more important, it's usually hidden under some manufacturer boot logo or whatsoever ...


45

TL;DR Because it needs the least chip count and thus makes it the cheapest. It's a Sinclair. Full Story: The Sinclair ZX80 used a Z80A running at 3.25 MHz. But this chip was rated for 4 MHz. Why was it run below rated speed? And the chip would have run for sure at more than 4 MHz. A computer design isn't about what a chip is rated, but what it's for. why ...


36

The PDP-10 had 'byte instructions' that could process a sequence of bytes of size 1 to 36 bits. The byte pointer was a word containing an 18-bit word address (and the usual index/indirect indications) plus position and size of the byte within the word. It was common to use 7-bit byte sequences for ASCII text, which gave 5 characters per word and one (...


32

Yes, it's possible to effectively change the volume if you're using Pulse Width Modulation (PWM), although the timbre of the note is also affected depending on playback hardware and psycho-acoustics. Dr. Blake Troise, who makes chiptunes under the moniker Protodome, describes how in a recent paper: The 1-Bit Instrument: The Fundamentals of 1-Bit Synthesis, ...


32

The main issue with the 80186 isn’t with the CPU core itself, but with its integrated peripherals: they aren’t compatible with those used in the IBM PC, and they aren’t integrated in the same way either. The IBM PC uses an 8237 DMA controller at offset 0x00 in the I/O address space, an 8259 PIC at offset 0x20, and an 8253 PIT at offset 0x40. The 80186’s ...


29

Your premise that the point of the Turbo button was originally to slow down the computer to be timing compatible to an IBM PC/XT is correct. There was demand for that function, because a some of software, mostly games, were not synchronized to any timing source, but just scaled with the CPU frequency. some examples I encountered at that time are: Bugs, 1982 ...


29

PIC: 7 bit address space The Microchip PIC family of CPUs specifically the 10, 12 and 16 series have 7 bits of address space. While 7 bits is not exactly 8 bits this shows that there are commercial CPUs still on sale and still widely used that have less than 8 bit address space (they are used for example for power management on some Macs and are the most ...


26

Write speed and endurance. Optical drive technology has been much slower to write to than magnetic Hard Disk Drives (HDDs). The erasable optical technologies that made it to mass market were much slower in write time than HDDs and in erase time. Their life before failure was in the 100's of erases. Optical drive use declined with the advent of USB flash ...


25

Classic RISC CPUs like ARM ... instructions execute in one cycle ... This assumption is not correct. The ARM-2 CPU (VL86C010, one of the first ARM CPUs) took: Only one cycle for most operations (as you expected it) Typically two cycles if a jump/branch was done Up to 4 cycles for shift/rotate operations Up to 16 cycles for multiply operations Up to 17 (or ...


24

If you watch enough YouTube videos of repairing old micros — and even ones that aren't that old (486s didn't come out that long ago, did they?) — you'll see a lot that have suffered some sort of damage due to storage over the years. Some damage, such as corrosion due to battery leakage or cracked circuit boards, is not due to climate. However ...


23

The [pre-AGA] Amiga: uses a planar frame buffer, stored in memory that is shared with the CPU (and which therefore reduces the CPU's speed); provides dual-playfield hardware scrolling, but the total bit fetch total per output byte doesn't stretch beyond six, so you end up with e.g. a 7 colour foreground and an eight colour background; provides 8 hardware ...


22

Short answer: If you are content with beeps, no. If you want arbitrary sound, yes. There's three ways to get sound out of the PC Speaker: Put the timer chip into square wave mode and send frequencies (actually countdowns) to the timer chip. This is cheap and what's used for most PC Speaker sound effects in games. 140Hz is a popular rate to do it at. Set up ...


22

The KENBAK-1 has 256 bytes of memory. I'm not certain whether it had an 8-bit PC. https://en.wikipedia.org/wiki/Kenbak-1


20

(From the perspective of the electronics, that means the displays were drawn sideways.) Not necessary. There is no inherent reason for drawing sideways. A video circuit can easy be made for either, as line width and number of lines can be defined either way. This is especially true for early games, where electronics were rather special to type and so was ...


19

The purpose of the switch is to support CPUs that can work at different clock frequencies. However, the presence of a turbo switch and a frequency display on a case, do not necessarily imply that the CPU can actually work at different clock frequencies, because the case is a generic case which has not been designed for one specific CPU. Background I ...


19

I think the best you could do in some cases was alter the pulse width of the basic square wave the hardware could produce. That wouldn't really change the volume, but you could make the tone "thinner" or "fatter" at the same frequency. One advanced technique used by some composers and sound drivers was "dithering", in which high-frequency random noise was ...


19

That paragraph should be understood in the context of the preceding paragraph: The PC speaker was often used in very innovative ways to create the impression of polyphonic music or sound effects within computer games of its era Effects such as those used in Pinball Fantasies in particular involve very rapid changes to the sound output by the PC speaker, ...


18

The ST-238R shown in the image is an RLL (Run Length Limited) drive and will not work correctly with a standard MFM controller, although it has the same ST506 electrical interface and cabling. To read back your data, you will need an RLL controller, which unfortunately are less common than MFM controllers and might not be easy to find. RLL is an encoding ...


17

Hardware of this sort has to be able to cope with the worst-case scenario in any given dot-clock cycle. So it has to look at the top layer pixel, determine whether that is transparent, and if so go down to the next layer and repeat. Only when it finds an opaque pixel (which may be the background) can it determine the colour to drive the video output with. ...


17

First, it is not true that the 486 executes instructions in a single cycle. The 80486 is a pipelined architecture, so it's more accurate to say that most instructions can start one cycle after the preceding instruction has started. The pipeline length of an 80486 is 5 stages (IF → ID1 → ID2 → EX → WB). This means that an instruction ...


17

Full disclosure: I worked on the x87 FPU of a 486-class CPU at a math-coprocessor company in the early 1990s and thereafter worked at AMD, where I was on the 3DNow! design team and the design team for the FPU of the AMD Athlon processor (also known as K7). The x87 FPU never acquired a flush-to-zero mode. In fact, denormal support was one of the major ...


16

It should be feasible to manufacture NMOS-process parts using 0.6µm equipment that is still in current use. WDC's W65C02S, as well as their other current products, are made at TSMC on 0.6µm, though they are CMOS chips. You would need to obtain examples of the original masks, have them converted to a format usable by the newer equipment (probably whole-...


16

'Jeff Porter realized it would not be possible to significantly cost reduce the Amiga 500 to get it into the $250 retail price range'. They could have cost-reduced the A500 - perhaps even to $250 retail - but they would have had to make some compromises that (thankfully) they weren't willing to do. There were a lot of chips on the board. They needed ...


16

The Nintendo 64 not only has full-perspective texturing, it can afford bilinear filtering — for each output pixel the PS1 samples the input texture exactly once. The N64 samples it four times and linearly interpolates according to how close it is to each (in two dimensions, hence bilinear). The Saturn has a couple of tricks up its sleeve: the primitive is ...


16

The amplifier input is biased to about half supply voltage. The SID output is also biased to about half supply voltage. You have little or no bulk/bypass capacitance on the 9V supply pins, so abruptly disconnecting the 9V supply from amp also abruptly shuts down the amp input bias. But as you have the quite excessively large 22uF coupling capacitor between ...


15

In short, 3 µm looks like it was available at the time, The questions are rather: to whom it was available and is it worth the investment. Processes aren't anything you'd buy from some supplier but develop in house. The fact that Intel got a 3 µm process does not translate to any other manufacturer being able to do so and more important doing so. ...


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