45

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 it run below rated speed? And the chip would have run for sure at more than 4 MHz. A computer design isn't about what a chip is rated, but what it's for. why ...


45

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 display hardware that is very closely tied to the architecture of the Z80. On the two first models, ZX80 and ZX81, the video display hardware was kept to a minimum, ...


39

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 point number every time they are evaluated. This is a time consuming process. Assigning the number once to a variable to be used thereafter will skip this part ...


36

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 keywords in full which were then immediately tokenised when you pressed enter. If anything, tokenised Sinclair BASIC generally had longer byte sequences than ...


22

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, with 62271 being the largest. Using the so called German Tank Formula, as traal suggested, yields 63685 as a result. So it might be safe to assume that there ...


21

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 lower than they were charging their other 68000 customers. Secondly, the pin count issue was key: for the custom chips, going anything over a 40 pin PDIP ...


20

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 studying BASIC loaders for ZX Spectrum games. You see, yes, Spectrum has more memory, but when the machine code program is loaded, it was absolutely not uncommon ...


19

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 and programmatically generate vertical syncs, which requires it to be in a loop that is tightly synchronised to the video signal. It's able to do a fixed-length ...


18

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 compete at the forefront used RAMs as gateways to technological development. (*1) Anyone not ramping up their output fast into the upper 90s will lose money. ...


13

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 program exits (or displays a scroll? prompt) while the lower screen is disabled, but the following program demonstrates the principle: 10 POKE 23659,0 20 PRINT AT ...


13

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. Common computers that had it at the time were the Sage and Sun range of workstations, the most common, "mass-market" computer that featured it was ...


12

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. Every fraction of a penny saved was important. I've recently looked into the Sinclair QL [...] yet it is purely 8bit machine I'd say it's an 8 bit system ...


9

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. The ZX80 has its expansion port on bavk side, all the way to the left, while the ZX81 got it moved over to the right side. Only a package not much wider than the connector would fit both equally well. ZX80 ...


9

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 discrete DC-DC converter - that's all the little pieces on the second board. The difference between the RAM-Packs for ZX80/81 is all in the colour :) In fact, ...


9

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 Microdrives use standard, two-track heads, apparently from some dictaphones. It's unlikely they deeply looked into compact cassette technology, given all these ...


9

##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, including 4 M of Spectrums. So my guess is, that it's for one a very rough number, but more important the author simply used the wrong label for the additior. Deails: ...


8

[...] 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 implementations. In this case it's due to integer vs. floating point maths. The fact is marked in the ZX80 entry by noting 'integer only'. The numbers shown are ...


8

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) third party vendors made theirs offering a pass-through. Did one or the other have a pass-through for the expansion bus? When the ZX-Printer came for the ...


7

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 support 7 bit (128 rows) refresh mode. Not that I know. Which are the "standard factory modifications"? The only one I know of is that weird capacitor connected to ...


7

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 expansion kit would cost more than the base model machine itself. Sinclair was very clever at squeezing a working system into the smallest possible memory ...


7

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 least 960 bytes, leaving only 64 bytes for BASIC code. Increasing the RAM size would have raised the price point, and "Under £100" was crucial to the early ...


7

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 possible they might want to.


6

Answering your rephrased question: The master clock could have run at 8 MHz, but that would have meant pixels being narrower than if generated by a 6.5 MHz clock. As the computer was built with a horizontal resolution of 256 pixels in mind (the time spent by 32 NOP instructions), the border area would have been enlarged, resulting in a smaller display. ...


6

As Uncle Bod already pointed out, the QL did not leave out Rubout (as Sinclair called it). It's just not printed at the keycap. CTRL+<-, a combination that seams quite logical to me, will work as expected. Having it as shifted function of on another key isn't as unusual as it seams. Already the ADM-3A did place RUB as SHIFT+-(*1), which in turn took the ...


5

I don't know about the normal printing routines in ZX Spectrum BASIC, but you can directly access the screen memory using POKE from BASIC. You'll need to work out where to get the 8 bytes of bitmap data comprising the character, then POKE them into the 8 bytes (on a 256-byte stride) corresponding to the desired character cell. According to this, the first ...


5

The easiest way to tell is by looking at the traces on the board. If they look curvy, as though hand-drawn, it's an issue 1. If they're in more or less straight lines, it's a 2 or 3. Seeing as issue 2 boards are exceedingly rare in the wild, it's almost certainly the latter. You can confirm this by looking for the issue number on the board, which should ...


5

Three jump direct to mind: Schneider Euro-PC and Euro-PC II Amstrad PPC Vendex Headstart Explorer Laser Compact XT by VTech (thanks mnem) Not to mention the WEB-IT, a 486 based as an all in one unit, introduced as late as 1998.


4

Pokemon on the German ZX Forum has designed a number of video improvement circuits (ZX81CPP, ZX81SCP) that allow connection of a composite video monitor and produce a crystal clear picture once properly adjusted. https://www.sinclairzxworld.com/viewtopic.php?f=8&t=841&sid=9e23e93b43bfcc0bb782a80803430e70 The circuit basically completely re-creates ...


4

In complement to the other answers, never forget that in the 1980s memory was expensive. For a 16-bit system, the base memory and every expansion costs twice the price of an 8-bit system - perhaps £100 more at the time. This is a big reason why Intel sold so many 8088s (there were other cost savings in bus buffers and PCB). Motorola tried to follow suit with ...


4

(No definitive answer, just some thoughts) Tape size isn't a major indicator as custom size manufacturing isn't a big deal. Already the Exaton Stringy Floppy of 1978, which can be seen as predecessor, did use a 1.6 mm tape. Similar BSR's wafer drive, used in the Rotronics Wafadrive or the Quick Data Drive for Commodore computers (*1), which used, IIRC, as a ...


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