143

Simple: Complexity. A 8088 had about 29,000 transistor functions, while an 8087 with 45,000 is almost double that. Integrating the FPU within the CPU would have made it three times as big, putting production at a >5 times higher failure rate, resulting in a price tag way higher than 3 times the CPU alone. More like 5-8 times. When closing in to what is ...


64

So these math chips (I assume you're talking about floating point units, such as the 8087 and other coprocessors) were not always/usually included in the CPU because they were not required by most users. When you don't need floating point maths, you also don't need the FPU, and that was the commonest case. So to make the CPU cheaper they leave it out. Then ...


50

Another point not addressed in the existing answers relates to the latency associated with accessing an external coprocessor. The first math coprocessors, while much faster than doing the same work on a CPU, still took many clock cycles to complete each operation. The overhead (bus cycles) associated with transferring data between the two chips was "lost in ...


38

The differences between PC floppy drives and Amiga floppy drives are as follows: PC floppy drives normally answer to drive select 1 (DS1), internal Amiga drives answer to DS0 pin 34 on the connector is used for disk change on the PC, disk ready on the Amiga pin 2 on the connector is used for high-density detection on the PC, disk change on the Amiga So ...


38

It seems to me there are a number of factors involved, some of which have been addressed in other answers: design complexity cost (which largely results from the complexity) feature necessity time-to-market Regarding complexity, as Raffzahn explains, early FPUs were much more complex than the CPUs they complemented. This meant that they needed more ...


34

No, there is no simple one-to-one mapping for the pins. (Bolded signal names will be active-low.) For example, while the 286 has two physical pins for interrupts (INTR and NMI), 68000 has three (IPL0, IPL1 and IPL2), encoding a total of 7 interrupt levels. So the interrupts are handled differently, and also the signaling for acknowledging an interrupt at ...


28

If you look into real hardware (like a Motorola/Freescale/Rochester 68060, which is long out of mass production): Modern CPUs (mainly Intel) boosted to several GHz clock frequency have one main technical limit: how to get the heat away from the sensitive silicon. There is a lot of clever technological magic involved to do that: powering down parts of the ...


24

It all depends on the computer to be modified and its RAM system. For now, let's focus on the pure RAM expansion issue and drop the part about bank switching; as this is completely machine-dependent, a generalized answer, as requested, will be impossible. Even so, there are still many hurdles to overcome. One after the other: RAM Type Some machines, like ...


21

Nothing stops anyone from creating faster accelerator cards (assuming Amiga or Atari ST - the only two platforms allowing for proper expansion cards), but there would be at least 3 major things to consider: CPUs: as far as I know, the fastest "classic" 68k CPUs are about 60 MHz, with some revisions that can go as fast as 80 or even 100 MHz. For, ...


19

Most obvious question first: why not puting itn on a ISA Card and take over the bus instead? Given, there would be still some work to be done after asking for DMA and pulling /MASTER, but way less than emulating a totally different CPU protocoll. More like adapting to a weired memory subsystem. But for your points First, most obviously, they are completely ...


15

Nothing actually prevents anybody of creating 2GHz 68060-like CPU. Or even highly-speculative out-of-order 68k-compatible one. All you need is tens (if not hundreds or more) of millions dollars to be able to spin a production process at (for example) TSMC and a talented team that would be able to create RTL for such a processor, do a proper verification for ...


13

This simple answer is not enough room on a chip for the total transistor count given the limitations of the process technology of the day. As per Wikipedia on the Intel 8087: The 8087 was an advanced IC for its time, pushing the limits of period manufacturing technology. Initial yields were extremely low. This for the coprocessor all by itself. ...


11

The 4116 and 4164 have different pin allocations for the reason you'd expect: the 4164 has an additional address line (for two more bits of address in total because row and column are multiplexed). So you can't just drop one in, in place of the other. The 4116 also receives a 12v signal, which the 4164 doesn't. So you can't perform a straight substitution. ...


11

Memory beyond 48 KB on 8-bit Ataris is all based on bank-switching, since the 6502 processor only has 16 address lines. The CPU can address 64 KB total, and that has to include ROM and memory-mapped I/O (0xD000-0xD7FF) as well as RAM. On XL/XE Ataris, PIA Port B, at address 0xD301, is used to swap parts of physical memory in and out of various banks, so ...


11

Like anything else, in the end, it was "ease of use" for some value of "ease" and "use". The primary motivator was performance, the specialized processors are just an extension of the maturity of micro electronics and CPU design. Recall that the original computer were just discrete components. Then, as the ICs evolved, gates out of transistors, and flip ...


11

You can absolutely do this, I've used a 6 foot extension like this before on my 128DCR with no signaling issues. You are correct that you need all 25 pins wired straight through which a normal DB25m/f cable for serial / modem won't provide (and a normal Centronics cable obviously has the wrong connector on one end). You need to look for a IEEE 1284 DB25 M/...


9

Many small CPUs available and used today for embedded designs do not have an onboard floating point unit - most of the AVR and PIC series, MCS51, some ARM ... 8 bit single-chip microprocessors were meant at least as much, if not more, for the same market that microcontrollers and embedded CPUs target today. In that market, cost and power efficiency are ...


9

We're so used to hugely complex and dense chips these days it's easy to forget that there was a time when the 8086, with "only" 29,000 transistors (no on-chip cache of any kind), was at the edge of what could be done. To put it simply: It wasn't feasible because the chip would be too big to produce cost-effectively (die size, yield) Everything a math chip ...


8

I've seen a lot of information on CDTV ROM switchers, but it is still unclear to me what is the actual purpose of it. The CDTV is essentially an Amiga 500 sans keyboard and floppy but with CD and other additions. It uses an of the shelf Kickstart 1.3 ROM plus an extension ROM providing CD access, audio player and alike. But development didn't end with ...


8

A proper ISA IDE interface is quite simple, but not as easy as it might sound. There are some strange corner cases you should consider for full AT compatibility. You can find schematics for ISA IDE interface adapters in service manuals of computers slightly newer than you MFM portable computer. For example, check volume II of the Compaq Deskpro 386 technical ...


7

I haven't looked at the architectures, but I suspect that one factor will be that the architecture sometimes will have implicit assumptions about the micro-architectural implementation. To achieve a GHz clock frequency, modern processors use maybe between 8 and 15 pipeline stages - with the expectation that typically all of the stages can be in use by a ...


7

Many would agree that Motorola was in a much better position to develop their 68k into something fast and modern than Intel with their crufty x86 ;) But Motorola stopped and abandoned the 68k in favour the PowerPC (which today still is at the heart of IBM's 5+ GHz POWER CPUs). Most users of 68k CPUs switched to Intel or various RISC CPUs. Commodore and Atari ...


7

As you mentioned, you could upgrade TRS-80 Model 100's RAM to 32k. You can also get a REX chip, which uses the ROM expansion slot to provide additional flash memory. The TRS-80 Model 100 had several peripherals available (in addition to the acoustic coupler) including a cassette recorder, an external drive, a barcode reader, printers, and even a "Disk/...


7

The datasheet for that part can be found here, it lists the maximum for VBAT as 4.0 V, so yes you do need to regulate down from 5 V.


7

I think it may be as easy as connecting male pins from one side to corresponding female pins on the other side, Exactly that. but need reassurance please. Would be shame to blow something up. For what? I mean, which logic gives that a strict 1:1 connection can blow up anything? After all, i1:1 means that there are no other connections made, doesn't it? I ...


6

Many older architectures were designed so that the speed of internal operations would be well-balanced with the speed of memory technologies that were available at the time. They were also designed to balance the cost of circuitry within a microprocessor or microcontroller with the cost of required support circuitry. As technologies have changed, the ideal ...


6

A PC 1.44 drive, can be converted for use in an Amiga, in fact ANY Amiga can use it, but it will be limited to 880k (720k PC). The reasoning, is because PC 1.44 drive motor spins the disk at a different rate. Amiga HD (1.76MB) spins at 150RPM, where a PC drive rotates at 300RPM.


6

In general on old computers, the whole address space will be used in some way or other, even with less than 64 KB RAM (for ROM or I/O). So you'll have to do bank switching of some kind, or you loose the ability to use original software. That said, a common method to do RAM (or ROM) extension is "piggybacking": You solder a second RAM chip of the same type ...


6

That's CN13. The pins are documented here and have address and data lines as you would expect for memory, not the signals you would need for a floppy drive. I would connect a Gotek to the DB-23 connector on the rear panel.


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