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The ZX81 Turns 40

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Re: The ZX81 Turns 40

#21

Post by forinti »

klelatti wrote: post #20

One of the things that distinguished the ZX81 from its predecessor the ZX80 was the fact that the screen didn't go off when your program was running, which made it much more useful. The CPU was still driving the screen but interrupts ensured that it was doing so when needed so actual code execution was limited to times when it wasn't needed for the screen. This of course made it exceedingly slow. Not helped by the fa…

You could, for 170 pounds, get an Acorn Atom. It had 2KB of RAM (twice as much!), a proper keyboard, an excellent BASIC, and a video chip.

Re: The ZX81 Turns 40

#22

Post by ourcat »

I had one of these at age 10. I still have it (at age 50) and it still works. Also the printer and a roll of paper.

Whenever people ask me what my earliest memory is, I say the 16k RAM Pack. :)

Re: The ZX81 Turns 40

#23

Post by klelatti »

forinti wrote: post #21
klelatti wrote: post #20

One of the things that distinguished the ZX81 from its predecessor the ZX80 was the fact that the screen didn't go off when your program was running, which made it much more useful. The CPU was still driving the screen but interrupts ensured that it was doing so when needed so actual code execution was limited to times when it wasn't needed for the screen. This of course made it exceedingly slow. Not helped by the fa…

You could, for 170 pounds, get an Acorn Atom. It had 2KB of RAM (twice as much!), a proper keyboard, an excellent BASIC, and a video chip.

Wikipedia says that would be over £700 in 2019 money - too much for a 15 year old!

Besides the £170 Atom only had Integer Basic - we had real (sort of) floating point.

I'm still jealous of anyone who had an Atom though.

Re: The ZX81 Turns 40

#24

Post by TacticalCoder »

nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

> I’m glad I still have it, and the Spectrum and Amiga’s that followed.

I wonder how many of us still have them all... I probably sound like a broken record at this time but I still have my Atari 600 XL, Commodore 128 (which I was only using in C64 mode) and Commodore Amiga.

The 600 XL and 128 are still working and the Amiga is probably easy to fix.

Re: The ZX81 Turns 40

#25

Post by cesaref »

TacticalCoder wrote: post #24
nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

> I’m glad I still have it, and the Spectrum and Amiga’s that followed. I wonder how many of us still have them all... I probably sound like a broken record at this time but I still have my Atari 600 XL, Commodore 128 (which I was only using in C64 mode) and Commodore Amiga. The 600 XL and 128 are still working and the Amiga is probably easy to fix.

I ditched almost all my old computers as I upgraded, but i've still got my ZX-81 with a dk'tronics graphics rom, that was a killer combination in 1982 or whenever!

The ones that have left the building include C64, C128D, Amiga 1000, Amiga 500, before I got my first 'proper' computer, a Mac IIcx which I had for many years running Logic. I'd like to say those were the days, but actually i get much more done and have more fun with modern computers, it's really just nostalgia for simpler times...

Re: The ZX81 Turns 40

#26

Post by bm98 »

criddell wrote: post #15
nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

I asked for a TI-99/4A because that's what my best friend had and we would make games and share them with each other. When I think back to the microcomputers of the early 80's, I'm kind of astounded that they sold in the numbers they did. They were pretty useless.

1982 Atari 800 here (was 8 years old at the time). I remember thinking the same thing at the time. When we first bought the thing, there just wasn't much I/O beyond the tape drive (and later the disk drive), and therefore the things we could do seemed very limited. It wasn't until we got a printer (a Star Micronics SG-10 dot matrix tractor feed) and a 300-bps modem that the world really opened up!

Re: The ZX81 Turns 40

#27

Post by [deleted] »

nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

[deleted]

Re: The ZX81 Turns 40

#28

Post by rwmj »

trynton wrote: post #19

According to something I read somewhere. The ZX81 floating routines did incorperate some unique math: (2^32) - ((2^32)-1) did not return 1 And the group of Cambridge mathamaticians that wrote the ROM turned out to be one man. "ZX81 ROM Assembly Listing" https://www.tablix.org/~avian/spectrum/rom/zx81.htm

I just tried it on the ZX81 online emulator: http://www.zx81stuff.org.uk/zx81/jtyone.html

You have to type the following sequence of keys:

  P  [Shift]I  2  [Shift]H  3  2  [Shift]O  -
  [Shift]I  [Shift]I  2  [Shift]H  3  2  [Shift]O
  -  1  [Shift]O  Enter
which should appear as:

  PRINT (2**32)-((2**32)-1)
It prints 0 which is not the expected answer! (The 0/0 at the bottom of the screeen is an OK message, the answer is printed in the top left corner). I think this isn't necessarily a bug, it's because the computer used something similar to modern single precision floating point.

Also try this (SQR is entered as: [Shift]Enter H):

  PRINT SQR 0.25
On the emulator it looks like the bug has been fixed, but on early models of the real hardware it would give a completely bogus result.

I think what was interesting was it used a kind of bytecode to run maths routines (similar to the Apple II's SWEET16 code).

Re: The ZX81 Turns 40

#29

Post by MaxBarraclough »

FabHK wrote: post #18
nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

> Incredibly, the ZX81 hardware and software scene is still alive. Indeed. Here the German ZX81 User group: http://www.zx81.de/ http://www.zx81.de/zxcms/English.html They’ve managed to turn a ZX81 into a web server: http://zx81-siggi.zx-team.org/ZxTeaM (I hope it survives being HN‘d…)

> (I hope it survives being HN‘d…)

Looks like we sunk it.

Re: The ZX81 Turns 40

#30

Post by TheOtherHobbes »

criddell wrote: post #15
nickt wrote: post #11

In terms of ROI, the best £69.95 I ever spent (I still have the receipt from WH Smith). It wasn’t the first computer I ever used, but it’s the first one I ever owned at age 9 and it led me down the path that’ll be familiar to many here... I’m glad I still have it, and the Spectrum and Amiga’s that followed. Incredibly, the ZX81 hardware and software scene is still alive. You can get parts for it quite easily, includi…

I asked for a TI-99/4A because that's what my best friend had and we would make games and share them with each other. When I think back to the microcomputers of the early 80's, I'm kind of astounded that they sold in the numbers they did. They were pretty useless.

They were imagination amplifiers. The computer itself didn't do much so you had to fill in the gaps by imagining the things it wasn't doing - often guided by some exciting cover art on books and games packaging.

You could also expand your imagination by thinking of the things you might do if you worked hard at it, or if it was only slightly bigger/faster/better.

Modern computing is the opposite. It does so much it doesn't leave any gaps for your imagination to fill - the creative equivalent of a distracting wall of noise for you to consume.

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