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47 votes
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Why did Sinclair choose the Z80 for its range of home computers?

Sinclair didn't always use the Z80 for its computers. The MK14 computer, sold in kit form (like the ZX80 was), used a National Semiconductor INS8060. The ZX range of home computers have a video ...
mcleod_ideafix's user avatar
46 votes
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Why did the ZX80 CPU run at only 3.25 MHz?

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 ...
Raffzahn's user avatar
  • 224k
45 votes
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Why does this BASIC program declare variables for the numbers 0 to 4?

These tricks are usually done to increase speed or reduce space. For most (especially Microsoft) BASIC, constants are stored within a tokenized line as ASCII (as entered), and converted to a floating ...
Raffzahn's user avatar
  • 224k
44 votes
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Why does the ZX81 not have user definable characters without extra hardware i.e. why could the character ROM not be in RAM?

The ZX80 and ZX81 use the Z80’s opcode fetch bus cycle for graphics collection — the opcode fetch is appropriated to obtain a character index and the refresh cycle is used to obtain a row of pixels. ...
Tommy's user avatar
  • 37.3k
39 votes
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ZX Spectrum tokenisation

Contrary to other answers, obliging the user to enter BASIC tokens directly doesn't really save meaningful amounts of RAM. Many of its contemporaries such as the BBC Micro had BASICs where you typed ...
pndc's user avatar
  • 11.4k
33 votes

What made some 8-bit BASIC interpreters especially slow?

"Atari BASIC: The Good, the Bad, and the Ugly" is an excellent summary Atari BASIC's advantages and weaknesses. To answer the Atari half of your question: How did it get so slow? Basically ...
Jim Nelson's user avatar
  • 3,773
27 votes

What made some 8-bit BASIC interpreters especially slow?

Commodore BASIC suffered from four major performance issues: It stored numbers as text in the source, and had to parse numbers every time they were used. Program lines are stored as singly-linked ...
doug65536's user avatar
  • 371
25 votes

Cambridge Z88 Production Run

I know it's bad style to answer ones own question. Still,I feel the need to publish my findings (*1): Over the last 3 18 26 months 5 years(*2) I've been able to collect serial numbers of 56 different ...
Raffzahn's user avatar
  • 224k
24 votes
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Were there really any cost savings in Sinclair QL because of it being 8-bit design with 8-bit bus 68k CPU?

Yes, there was a significant cost saving. For a start, Motorola charged us something like 30-40% less for the 68008 (I forget the exact amount, but it was substantial), because the price was so much ...
xgretsch's user avatar
  • 356
22 votes

Why does this BASIC program declare variables for the numbers 0 to 4?

The answer by Raffzahn is very good, except that I disagree that ZX80/81 background is all that important and I also feel he missed one important trick. I personally know most of these tricks from ...
introspec's user avatar
  • 4,172
22 votes

What was Sinclair's intention with the Microdrive?

I think the story of the Sinclair Microdrive fits nicely with similar stories of other data tape drives offered at the same time. In the early 1980's, there was at least the Sinclair Microdrive, ...
Brian H's user avatar
  • 60.8k
21 votes

ZX Spectrum tokenisation

A purely speculative answer: it's a user experience improvement. The ZX80 is unable both to process keyboard input and to maintain a stable display. It has the Z80 itself step through display bytes ...
Tommy's user avatar
  • 37.3k
21 votes

Is there any significant difference in Sinclair BASIC of ZX80, ZX81 and ZX Spectrum?

Spectrum BASIC is a superset of the earlier BASICs (all the colour commands, etc), so pedantically the answer to the question is the title of the post is "yes, there are significant differences&...
Philip Kendall's user avatar
20 votes

Why does Sinclair BASIC have all of the characters twice in the token table?

You're right; the ZX81 does not use ASCII. That's because it uses the CPU to generate the displayed picture, from a compressed format in memory. The way this works is an absolute freakshow*, but from ...
Omar and Lorraine's user avatar
19 votes
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When did half-bad RAM chips stop being available?

Sinclair's use was a very unique case in a very specific situation that never occurred again later on. Production side: There were many more manufacturers of chips back then. The ones that wanted to ...
Raffzahn's user avatar
  • 224k
16 votes
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Is it possible to PRINT AT 23,0 in ZX Spectrum BASIC?

POKE 16418,0 is for the ZX81, not the Spectrum - the equivalent system variable on the Spectrum is at 23659. You need to take care when poking this address, as it's liable to cause a crash if the ...
gasman's user avatar
  • 1,341
15 votes

Were there really any cost savings in Sinclair QL because of it being 8-bit design with 8-bit bus 68k CPU?

By the time the QL was first designed (starting as a "ZX83" in early 1983), a full-blown 8MHz 68000 was not a mass-produced, cheap commodity item, but rather a pretty expensive beast to buy. ...
tofro's user avatar
  • 35k
15 votes

What does Spectrum BASIC have that ZX81 lacks?

From 'Reusing Code, Reverse Engineering And Collaboration': Grant and Vickers would’ve liked to start over, but there wasn’t time. So the ZX81 BASIC was used as the starting point, with the addition ...
Mark Williams's user avatar
14 votes
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How did the ZX80 RAM pack use DRAM?

But as I understand it, the then current 16kbit RAM chips actually required three different voltages: -5, +5, +12. Right, and the 'missing' voltages (-5V,+12V) get generated from the +9V source via a ...
Raffzahn's user avatar
  • 224k
13 votes
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Why did the ZX81 16K RAM pack use two PCBs?

It was neither due history or electronic but for design reason: The 16 KiB RAM pack was intended to be sold to existing (and new *1) ZX80 users as well. While both had their expansion port on back ...
Raffzahn's user avatar
  • 224k
13 votes

Were there really any cost savings in Sinclair QL because of it being 8-bit design with 8-bit bus 68k CPU?

TL;DR: It was all about the incredible low price of 400 GBP. Outclassing any other 16 bit system (except for the TI 99/4) by at least a magnitude, on par or undercutting actual 8 bit machines as well. ...
Raffzahn's user avatar
  • 224k
13 votes

What was Sinclair's intention with the Microdrive?

That product decision was very probably driven in a big part by Sinclair's (both the company and the man himself) fascination for aggressively simplified technical solutions and shifting the task from ...
tofro's user avatar
  • 35k
11 votes

What made some 8-bit BASIC interpreters especially slow?

Oric BASIC was slow for several reasons I can think of like most interpreted BASIC flavours, it used floating point for numeric variables by default. One could use integer types (ex: A%) but in ...
Jean-François Fabre's user avatar
10 votes
Accepted

Can you switch the ZX81 ROM to RAM w/o write protecting it and still use ZX81 BASIC?

Directly to answer your question: yes, if the RAM copy is substituted after the machine has started up; otherwise, not reliably, as it's likely the first five bytes have been altered. With reference ...
Tommy's user avatar
  • 37.3k
10 votes
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Using Sinclair ZX Microdrive is it possible to random access a text-file?

Let's have few functions and (system) variables names 15 DEF FN p(a)=256*PEEK (a+1)+PEEK a : REM DPEEK(a) 16 DEF FN m(n,d)=n-d*INT (n/d) : REM MOD(n,d) 17 DEF FN l(v)=v-256*FN h(v) : ...
Matteo Vitturi's user avatar
10 votes
Accepted

What does Spectrum BASIC have that ZX81 lacks?

Hopefully, this is a pretty comprehensive list of the differences between the ZX81 and Spectrum (and, to a lesser extent, the ZX80) BASICs: String handling No FAST and SLOW UNPLOT/PLOT OVER ...
Greenonline's user avatar
  • 4,386
9 votes
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Did the ZX80 RAM pack pass the expansion bus through?

Did one or the other have a pass-through for the expansion bus? There was no other peripheral (by Sinclair) for the ZX80 than the 1..3 KiB static RAM or the later 16 KiB DRAM version (*1). Most (*2) ...
Raffzahn's user avatar
  • 224k
9 votes

Sinclair's microdrive -- was it based on compact cassette technologies?

The tape was actually the same quality as used for VCR tape - according to the QL Service manual "high-quality video tape" was used. Other than the rotating heads in VCRs, however, Sinclair ...
tofro's user avatar
  • 35k
9 votes
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What non-Spectrum computers did Sinclair sell 4 million of?

##TL;DR: Not really sure where this claim of over 5 M computers, including 1 M Spectrum comes from. While still not correct, it would sound more believable the other way around, as 5 M units, ...
Raffzahn's user avatar
  • 224k
8 votes

Why did the Sinclair QL keyboard lack a Delete key?

As Uncle Bod already pointed out, the QL did not leave out Rubout (as Sinclair called it). It's just not printed on the keycap. CTRL+⇐, a combination that seems quite logical to me, will work as ...
Raffzahn's user avatar
  • 224k

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