5 ms·

> In any case, I did not find the protected mode. Because, unless I'm misunderstanding the video, it doesn't exist until you add a whole bunch of external hard

> In any case, I did not find the protected mode. Because, unless I'm misunderstanding the video, it doesn't exist until you add a whole bunch of external hardware (which is why the video is clickbait - a fact he acknowledges later.)

visarga 4y ago
Just a flip flop and an OR gate.
qwerty456127 4y ago
> until you add a whole bunch of external hardware Why mind this if the hardware to add is the same level of technology like Z80 itself? I would be glad to build a computer as advanced as possible combining some Z80s and additional HW.
- zimpenfish 4y ago
  > Why mind this if the hardware to add is the same level of technology like Z80 itself? But it's not "the Z80's protected mode" - it's "the Z80 + an extra circuit to emulate protected mode". It's a super clever hack, yes! But filthy clickbait also.
  - mannykannot 4y ago
    There’s a small irony in your clickbait complaint containing a misrepresentation of the content.
moron4hire 4y ago
It's not uncommon for chips to support configuring different features by wiring in external components. Though usually they are passive components, this isn't completely absurd.
korfuri 4y ago
I mean, true, but "a whole bunch" is kind of misleading. It's a really clever hack using really a tiny amount of extra gates. It's still a very cool and innovative hack that nobody really had thought about before.
- kazinator 4y ago
  Using external signals for some sort of protection isn't innovative. This is a documented feature of the Intel 8086: the S3 and S4 pins expose which memory segment is being accessed: code, data, stack or extra segment.
- vintermann 4y ago
  Reminds me of the printer interrupt hack Darklite/Offence used for their Tiki-100 demos. The Tiki-100 is an obscure Norwegian 8-bit computer from 1984, also Z80-based. It had nice graphics for its time, with 16 colours from a 256-colour palette. However, it was very hard to use productively, since the machine had no video sync interrupts. What the guys in the demogroups figured out, was that it did have parallel port interrupts, and with a tiny hardware mod (just a wire from the expansion port to the parallel port), they could "steal" those for Commodore 64-style raster interrupts.
  - actionfromafar 4y ago
    Heck, one could connect a Commodore 64 to the Tiki and get synced frames.
- rep_lodsb 4y ago
  It certainly has been thought of before. Using external circuitry to remap the address space was common with lots of different processors, and once you have that (and a way to jump to a controlled address from hardware) it's a logical next step. That it wasn't something usual with microcomputers of the time wasn't because it would have required some uniquely clever design. Rather it had to do with them being single-user/single-task, with simple operating systems where programs were expected to have full access to the machine.
II2II 4y ago
Sure, but if memory serves me correctly, many early workstations used a microprocessor with an external MMU. It is misleading in the sense that it is not part of the Z80, but it is in the character of the times. (And MMUs are not the only CPU feature that was originally external. The FPU is an example that more people will be familiar with since it was an upgrade path available on many personal computers.)
- jandrese 4y ago
  I don't think MMUs were common on machines that ran on a Z80 however.
  - NegativeLatency 4y ago
    For example a Programmable MMU was an optional add on for the Macintosh II (which wasn’t a z80 but serves to illustrate the time when they began to become available to home computers)
  - DonHopkins 4y ago
    The home-brew pager (MMU) of the MIT-MC PDP-10 KL10 was appropriately called "KL-UDGE". (KL was the prefix of the PDP-10 model). https://en.wikipedia.org/wiki/Kludge https://en.wikipedia.org/wiki/Kludge It's on display at the Paul G. Allen Living Computer Museum. https://sites.google.com/site/mthompsonorg/Home/pdp-10/pdp-10-serial-numbers https://sites.google.com/site/mthompsonorg/Home/pdp-10/pdp-1... https://donhopkins.com/home/catalog/images/mc-console.jpg https://donhopkins.com/home/catalog/images/mc-console.jpg Lars Brinkhoff has taken photos of the KL-UDGE blinken lights panel and naked wire wrap boards: https://twitter.com/larsbrinkhoff/status/1128601896619524097 https://twitter.com/larsbrinkhoff/status/1128601896619524097 >Photo 6/7: KL-UDGE lights panel >Photo 7/7: KL-UDGE boards. Real-time time of day clock?
    - wk_end 4y ago
      Was on display. The LCM closed due to COVID and there's no indication that it's coming back, sadly.
  - 4y ago

visarga 4y ago

Just a flip flop and an OR gate.

qwerty456127 4y ago

> until you add a whole bunch of external hardware Why mind this if the hardware to add is the same level of technology like Z80 itself? I would be glad to build a computer as advanced as possible combining some Z80s and additional HW.

zimpenfish 4y ago
> Why mind this if the hardware to add is the same level of technology like Z80 itself? But it's not "the Z80's protected mode" - it's "the Z80 + an extra circuit to emulate protected mode". It's a super clever hack, yes! But filthy clickbait also.
- mannykannot 4y ago
  There’s a small irony in your clickbait complaint containing a misrepresentation of the content.

moron4hire 4y ago

It's not uncommon for chips to support configuring different features by wiring in external components. Though usually they are passive components, this isn't completely absurd.

korfuri 4y ago

I mean, true, but "a whole bunch" is kind of misleading. It's a really clever hack using really a tiny amount of extra gates. It's still a very cool and innovative hack that nobody really had thought about before.

kazinator 4y ago
Using external signals for some sort of protection isn't innovative. This is a documented feature of the Intel 8086: the S3 and S4 pins expose which memory segment is being accessed: code, data, stack or extra segment.
vintermann 4y ago
Reminds me of the printer interrupt hack Darklite/Offence used for their Tiki-100 demos. The Tiki-100 is an obscure Norwegian 8-bit computer from 1984, also Z80-based. It had nice graphics for its time, with 16 colours from a 256-colour palette. However, it was very hard to use productively, since the machine had no video sync interrupts. What the guys in the demogroups figured out, was that it did have parallel port interrupts, and with a tiny hardware mod (just a wire from the expansion port to the parallel port), they could "steal" those for Commodore 64-style raster interrupts.
- actionfromafar 4y ago
  Heck, one could connect a Commodore 64 to the Tiki and get synced frames.
rep_lodsb 4y ago
It certainly has been thought of before. Using external circuitry to remap the address space was common with lots of different processors, and once you have that (and a way to jump to a controlled address from hardware) it's a logical next step. That it wasn't something usual with microcomputers of the time wasn't because it would have required some uniquely clever design. Rather it had to do with them being single-user/single-task, with simple operating systems where programs were expected to have full access to the machine.

II2II 4y ago

Sure, but if memory serves me correctly, many early workstations used a microprocessor with an external MMU. It is misleading in the sense that it is not part of the Z80, but it is in the character of the times. (And MMUs are not the only CPU feature that was originally external. The FPU is an example that more people will be familiar with since it was an upgrade path available on many personal computers.)

jandrese 4y ago
I don't think MMUs were common on machines that ran on a Z80 however.
- NegativeLatency 4y ago
  For example a Programmable MMU was an optional add on for the Macintosh II (which wasn’t a z80 but serves to illustrate the time when they began to become available to home computers)
- DonHopkins 4y ago
  The home-brew pager (MMU) of the MIT-MC PDP-10 KL10 was appropriately called "KL-UDGE". (KL was the prefix of the PDP-10 model). https://en.wikipedia.org/wiki/Kludge https://en.wikipedia.org/wiki/Kludge It's on display at the Paul G. Allen Living Computer Museum. https://sites.google.com/site/mthompsonorg/Home/pdp-10/pdp-10-serial-numbers https://sites.google.com/site/mthompsonorg/Home/pdp-10/pdp-1... https://donhopkins.com/home/catalog/images/mc-console.jpg https://donhopkins.com/home/catalog/images/mc-console.jpg Lars Brinkhoff has taken photos of the KL-UDGE blinken lights panel and naked wire wrap boards: https://twitter.com/larsbrinkhoff/status/1128601896619524097 https://twitter.com/larsbrinkhoff/status/1128601896619524097 >Photo 6/7: KL-UDGE lights panel >Photo 7/7: KL-UDGE boards. Real-time time of day clock?
  - wk_end 4y ago
    Was on display. The LCM closed due to COVID and there's no indication that it's coming back, sadly.
- 4y ago