46
votes
Accepted
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 ...
- 195k
46
votes
Accepted
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 ...
- 18.3k
44
votes
Accepted
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 ...
- 195k
44
votes
Accepted
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. ...
- 33.8k
38
votes
Accepted
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 ...
- 10.1k
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 ...
- 3,483
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 ...
- 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 (*2), I've been able to collect serial numbers of 44 different Z88s, ...
- 195k
23
votes
Accepted
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 ...
- 346
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 ...
- 4,012
20
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 ...
- 33.8k
20
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&...
- 527
19
votes
Accepted
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 ...
- 195k
16
votes
Accepted
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 ...
- 946
16
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, ...
- 59.1k
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. ...
- 30.1k
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. ...
- 195k
12
votes
Accepted
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 ...
- 195k
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 ...
- 10.2k
9
votes
Accepted
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) ...
- 195k
9
votes
Accepted
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 ...
- 195k
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 ...
- 30.1k
9
votes
Accepted
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, ...
- 195k
9
votes
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 ...
- 33.8k
8
votes
Accepted
Why is ZX80 much faster than Spectrum on Rugg/Feldman benchmarks?
[...] Sinclair ZX80 is much faster than Sinclair Spectrum on all tests despite the fact that both computers use the same CPU.
It's not about the CPU, but because these are vastly different BASIC ...
- 195k
8
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 ...
- 30.1k
7
votes
ZX Spectrum tokenisation
I wasn't necessarily easier - it was down to money.
Remember these were the days when the single most expensive component of a computer was its memory. For many micros of the time, a simple memory ...
- 7,904
7
votes
Are all 64k x 4-bit ICs interchangeable for Amstrad-era ZX Spectrum 128k +2/+3?
Yes. Speed must be 150ns or faster, technology should be NMOS (CMOS produces too sharp edges that may cause ringing, due to non equalized traces in the PCB, so they may or may not work) and must ...
- 18.3k
7
votes
Why did the ZX80 CPU run at only 3.25 MHz?
The usual answer to questions on early Sinclair machines is "Because it was cheaper that way."
In this case, a 40-column screen, implied by 4MHz, would have increased the screen buffer size to at ...
- 9,713
7
votes
When did half-bad RAM chips stop being available?
The Memotech MTX (1984-5 or so) has a wire link on its circuit board that allows you to use half-good chips.
I dont think I’ve seen any being used, but it seems the designer thought it at least ...
- 121
Only top scored, non community-wiki answers of a minimum length are eligible