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ZX 81
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The
Sinclair ZX 81 was the successor of the ZX 80, and can be regarded as an
evolution of it.
The ZX80 could not handle floating point numbers or cassette data files,
but the ZX-81 could. The ZX-80 had 4k ROM : the
ZX-81 had 8K ROM with 30 additional functions and some instructions to
drive the printer. Thanks to a higher level of integrations (the total
number of chips in the basic system was 4, against the ZX80's 21), the
ZX-81 cost £30 less than the ZX-80. The plastic case was also
different. Whereas the ZX-80 looked cheap in it lightweight white case, the
ZX-81 was beautifully designed in its black ABS plastic case.
The keyboard was still formed by an underprinted
plastic, but this one was made of non-reflective material. Even with this
slight improvement it was quite horrible to use, that's why a lot of
additional keyboards appeared quickly on the market. Some of the keys
sported up to 5 functions, right in the Sinclair tradition, accessible
through the "GRAPHICS", "SHIFT" and
"FUNCTION" keys.
Here are the functions added over the ZX-80 : ASN, ACS, ATN COS, EXP,
INKEY$, PI, SGN, SIN SQR, INT, LEN, LN, TAN, VAL, <=, >=, < >,
COPY, DIM A$, FAST, FOR ... TO ... STEP, LLIST, LLIST n, LPRINT, PAUSE,
PLOT, PRINT AT, PRINT TAB, SCROLL, SLOW, UNPLOT. Some are quite useful and
make you wonder how it was possible to make anything on the ZX-80 !? However, one function disappeared: TL$ which was
used to return a string minus its first character.
The ZX-81 could be operated in two modes, SLOW and FAST. The FAST mode
which was the only mode available on the ZX-80, only refreshed the display
when the system had completed computing, resulting in a painful screen
flicker! It was a useful mode when you had to do a lot of calculation
without the need to see what's going on all the time on the screen. The
SLOW mode, which was indeed quite slooooowwww,
behaved like all other computers did, refreshing the screen all the time.
The ZX81 contained only four main chips : the ROM,
Z80A CPU, 1K RAM and the Ferranti custom-made chip! It is as simple as
that. The machine was assembled by Timex Corporation in their Scottish
plant.
This computer was a very great success in Europe in the beginning of the
80's. It was very cheap and a lot of people who now are working on modern
PCs or Macs, made their first move on a ZX 81 even though its performance
was actually poor!
A very great range of peripherals were developed for this computer, among them : 3.5" floppy disk units, keyboards, high
resolution graphic cards, RS232 or Centronics
interfaces, RAM expansions, etc... In fact, it was possible to make a
pretty good computer from the ZX 81!
It was followed by the ZX-Spectrum and was also sold as the Timex Sinclair
1000 in the USA.
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NAME
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ZX 81
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MANUFACTURER
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Sinclair
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TYPE
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Home Computer
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ORIGIN
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United Kingdom
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YEAR
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march1981
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BUILTINLANGUAGE
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Sinclair Basic
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KEYBOARD
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Touch-sensitive keyboard,
40 keys
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CPU
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Zilog Z80A
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SPEED
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3.5
MHz
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RAM
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1 KB (901 bytes available, up to 64 KB)
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ROM
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8 KB
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TEXTMODES
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32 x 24 (but 2 lines are reserved for
system messages and commands)
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GRAPHICMODES
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64 x 44
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COLORS
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Black and white
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SOUND
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None
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SIZE/WEIGHT
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167 x 175 x 40 mm / 350gr
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I/OPORTS
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Z80
Bus, tape, video
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POWERSUPPLY
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9V DC , 600 mA (centre polarity = +ve)
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PRICE
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Kit :£50 (UK, june
1981) / Ready-built : £70 (UK, june 1981)
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