The Sinclair ZX80 launched in 1980 as the first complete home
computer available for under £100 – it also sold in kit form for £79.95. It may
have been a breakthrough, with both the ZX80 and its successor, the ZX81, introducing
home computing to millions in the UK, but that £100 price was achieved through
compromise that leaves it little more than that first step. Infamously, it only
had one kilobyte (1024 bytes) of RAM, when other computers came with at least
four times that amount. Its central processor, a Zilog Z80, also generated the video
display, meaning the press of a key caused interference with the picture. The
keys themselves were flat, requiring you to press through a membrane to the
motherboard itself. When the ZX81 was introduced in 1981, a “slow” mode fixed
the flickering screen, and £20 was knocked off the price, but if you wanted
more than 1K of RAM, you had to buy an expansion pack, required for most games.
(By the way, 1024 bytes is the space needed to hold this paragraph, including
spaces.)
The limitations of the ZX80 led to arguments that it cannot
really be called a computer, even for 1980. However, comparing it against the “1977
Trinity” - the Commodore PET 2001, the Apple II, and the Tandy TRS-80 Model I
all launched in 1977 – the ZX80 holds up reasonably well. The ZX80 could only
produce a monochrome display, but only the Apple II was capable of colour. All
of the computers have no lowercase text option except for the PET, but you
cannot mix them with capitals, with only an either/or option for all text. Only
the PET and Apple II had sound, a simple speaker to produce beeps, and only the
Apple II had the built-in instructions to load programs from a floppy disc –
the others would need to be expanded first.
The main contention over the ZX80 is the implementation of
the programming language BASIC, short for Beginner’s All-Purpose Symbolic
Instruction Code. This language overlays the assembly code that is being fed to
the processor, and is much easier to learn - even people who never used an old
computer know what a BASIC program looks like:
10 PRINT “HELLO”
20 GOTO 10
RUN
The Apple II and PET computers, like most at the time, would
license their versions of BASIC from Microsoft, but Sinclair would employ a
software company, Nine Tiles, to write their BASIC. However, the chip that
would hold it in the computer was to be only 4 kilobytes in size, restricting
the number of commands it could hold. Shortcuts to the commands it had were
laid across the keyboard, reducing the space in RAM needed to hold programs,
but one strange result of Sinclair’s BASIC was that the ZX80 could not
calculate decimal points.
You would expect a computer to divide 5 by 4 and give you
1.25, or divide 20,000 by 10,001 and give you 1.9998. In both cases, the answer
given by the ZX80 is just the integer “1”, making you wonder why you didn’t
just buy a scientific calculator from Hewlett-Packard instead. The instruction
manual doesn’t help this: it is named “A course in Basic Programming,”
cementing that this computer is only your first step into computers, but pages 36-38
provides a program for completing long division on your ZX80 to produce an
answer with decimal points, like you were using pen and paper anyway.
What the ZX80 missed was the ability to run floating-point
arithmetic, which is a way of calculating very large numbers. Basically (which
is the right word to use here), floating-point arithmetic as used by a computer
notes that the decimal point can be placed anywhere within a number, and you
can use an exponent to determine where the point should lie. One answer we
wanted earlier, “1.25”, can be written as 125 x 10-2 – this is
because we moved the decimal point two places to the right. We could also
express it as 12500000 x 10-8, if that proves more useful to a
computer.
Before processor clock speeds and numbers of cores became
the standard for how fast a computer is, it was previously how many floating-point
operations per second, or FLOPS, it can complete – for 1980, tens of thousands
of FLOPS is the standard, whereas an iPhone XS can do a billion FLOPS at least.
However, if your computer can do none at all, is it really a computer?
Then again, do you need them? One kilobyte of RAM is not
enough to do many things, let alone produce a display full of text, but you can
make games – the software company Psion, known later for their personal
organisers, fit Chess into 1K, minus a couple of rules. I have also seen the BASIC
program for a type of Space Invaders game, made mostly of “PRINT” commands to
draw the ships, and “LET” commands to apply values to them. Applying logic to the
ZX80 is fine, and the reason most games for the ZX81 required more memory was
because the games themselves were more elaborate. A popular early computing
project was the “TV Typewriter” of 1973, which existed only to put text on screen,
with homebrew projects adding memory chips and BASIC to them, and the ZX80,
with its motherboard of mostly logic chips, can be seen as an extension of
that.
Of course, the ZX81 added floating-point arithmetic to their
BASIC in 1981, with the success of the ZX80 having validated the idea of cheap
home computing. However, now that I know the Tandy TRS-80’s original BASIC chip
was a public-domain version that had floating-point arithmetic added to it, while
still fitting into the same 4K that Sinclair had, it makes me wonder why
Sinclair didn’t do that in the first place – the ZX80 was inspired by Clive Sinclair’s
daughter playing on her TRS-80, so it would have been worth a further look.
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