<s>
The	O
Sinclair	B-Operating_System
ZX80	I-Operating_System
is	O
a	O
home	O
computer	O
launched	O
on	O
29	O
January	O
1980	O
by	O
Science	O
of	O
Cambridge	O
Ltd	O
.	O
(	O
later	O
to	O
be	O
better	O
known	O
as	O
Sinclair	O
Research	O
)	O
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
was	O
very	O
popular	O
straight	O
away	O
,	O
and	O
for	O
some	O
time	O
there	O
was	O
a	O
waiting	O
list	O
of	O
several	O
months	O
for	O
either	O
version	O
of	O
the	O
machine	O
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
,	O
named	O
after	O
the	O
Z80	B-General_Concept
processor	O
,	O
was	O
designed	O
by	O
Jim	O
Westwood	O
.	O
</s>
<s>
It	O
featured	O
a	O
3.25	O
MHz	O
Z80	B-General_Concept
CPU	O
,	O
1	O
KB	O
of	O
static	B-Architecture
RAM	I-Architecture
,	O
and	O
4	O
KB	O
of	O
ROM	B-Device
.	O
</s>
<s>
The	O
machine	O
had	O
no	O
sound	O
output	O
and	O
used	O
a	O
simple	O
RF	O
connection	B-Protocol
to	O
display	O
on	O
a	O
household	O
television	O
.	O
</s>
<s>
The	O
firmware	B-Application
contained	O
the	O
Sinclair	B-Language
BASIC	I-Language
programming	I-Language
language	I-Language
,	O
editor	O
,	O
and	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
was	O
advertised	O
as	O
the	O
first	O
personal	O
computer	O
for	O
under	O
£100	O
and	O
received	O
praise	O
for	O
its	O
value	O
and	O
documentation	O
.	O
</s>
<s>
Original	O
ZX80s	B-Operating_System
in	O
good	O
condition	O
are	O
now	O
sought	O
after	O
by	O
collectors	O
.	O
</s>
<s>
Clones	B-Device
of	I-Device
the	I-Device
ZX80	I-Device
include	O
the	O
MicroAce	O
,	O
NE-Z80	O
,	O
and	O
the	O
Microdigital	O
TK80	O
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
was	O
named	O
after	O
the	O
Z80	B-General_Concept
processor	O
with	O
the	O
'	O
X	O
 '	O
meaning	O
"	O
the	O
mystery	O
ingredient	O
"	O
.	O
</s>
<s>
Internally	O
,	O
the	O
machine	O
was	O
designed	O
by	O
Jim	O
Westwood	O
around	O
a	O
Z80	B-General_Concept
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
with	O
a	O
clock	O
speed	O
of	O
3.25MHz	O
,	O
and	O
was	O
equipped	O
with	O
1KB	O
of	O
static	B-Architecture
RAM	I-Architecture
and	O
4KB	O
of	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
was	O
designed	O
around	O
readily	O
available	O
TTL	B-General_Concept
chips	O
;	O
the	O
only	O
proprietary	O
technology	O
was	O
the	O
firmware	B-Application
.	O
</s>
<s>
The	O
machine	O
was	O
mounted	O
in	O
a	O
small	O
white	O
plastic	O
case	O
,	O
with	O
a	O
one-piece	O
blue	O
membrane	B-Device
keyboard	I-Device
on	O
the	O
front	O
.	O
</s>
<s>
Display	O
was	O
over	O
an	O
RF	O
connection	B-Protocol
to	O
a	O
household	O
television	O
,	O
and	O
simple	O
offline	O
program	O
storage	O
was	O
possible	O
using	O
a	O
cassette	O
recorder	O
.	O
</s>
<s>
The	O
video	O
display	O
generator	O
of	O
the	O
ZX80	B-Operating_System
used	O
minimal	O
hardware	O
plus	O
a	O
combination	O
of	O
software	O
to	O
generate	O
a	O
video	O
signal	O
.	O
</s>
<s>
This	O
was	O
an	O
idea	O
that	O
was	O
popularised	O
by	O
Don	O
Lancaster	O
in	O
his	O
1978	O
book	O
The	O
TV	O
Cheap	O
Video	O
Cookbook	O
and	O
his	O
"	O
TV	B-Device
Typewriter	I-Device
"	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
this	O
approach	O
the	O
ZX80	B-Operating_System
could	O
only	O
generate	O
a	O
picture	O
when	O
it	O
was	O
idle	O
,	O
i.e.	O
</s>
<s>
However	O
,	O
the	O
ZX80	B-Language
character	I-Language
set	I-Language
included	O
some	O
simple	O
block-based	O
graphics	O
glyphs	O
,	O
allowing	O
basic	O
graphics	O
to	O
be	O
accomplished	O
,	O
with	O
some	O
effort	O
.	O
</s>
<s>
One	O
advantage	O
to	O
using	O
monochrome	B-Algorithm
video	O
is	O
that	O
different	O
colour	O
broadcast	O
standards	O
(	O
e.g.	O
</s>
<s>
PAL	B-Language
,	O
SECAM	O
)	O
simply	O
were	O
n't	O
an	O
issue	O
when	O
the	O
system	O
was	O
sold	O
outside	O
the	O
UK	O
.	O
</s>
<s>
The	O
ROM	B-Device
contained	O
the	O
Sinclair	B-Language
BASIC	I-Language
programming	I-Language
language	I-Language
,	O
editor	O
,	O
and	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
same	O
slot	O
bus	O
was	O
continued	O
on	O
the	O
ZX81	O
,	O
and	O
later	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
which	O
encouraged	O
a	O
small	O
cottage	O
industry	O
of	O
expansion	O
devices	O
,	O
including	O
memory	O
packs	O
,	O
printers	O
and	O
even	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
The	O
original	O
Sinclair	B-Operating_System
ZX80	I-Operating_System
RAM	O
Pack	O
held	O
either	O
1	O
,	O
2	O
or	O
3KB	O
of	O
static	B-Architecture
RAM	I-Architecture
and	O
a	O
later	O
model	O
held	O
16KB	O
of	O
dynamic	O
RAM	O
(	O
DRAM	O
)	O
.	O
</s>
<s>
Following	O
the	O
ZX81	O
's	O
release	O
,	O
a	O
ZX81	O
8KB	O
ROM	B-Device
was	O
available	O
to	O
upgrade	O
the	O
ZX80	B-Operating_System
at	O
a	O
cost	O
of	O
around	O
20%	O
of	O
a	O
real	O
ZX81	O
.	O
</s>
<s>
By	O
simply	O
taking	O
off	O
the	O
top	O
cover	O
of	O
the	O
ZX80	B-Operating_System
and	O
prying	O
the	O
old	O
ROM	B-Device
from	O
its	O
socket	O
and	O
carefully	O
inserting	O
the	O
new	O
ROM	B-Device
and	O
adding	O
the	O
keyboard	O
overlay	O
,	O
the	O
ZX80	B-Operating_System
would	O
now	O
function	O
almost	O
identically	O
to	O
the	O
proper	O
ZX81	O
–	O
except	O
for	O
SLOW	O
mode	O
,	O
due	O
to	O
the	O
differences	O
in	O
hardware	O
between	O
the	O
two	O
models	O
.	O
</s>
<s>
The	O
process	O
was	O
easily	O
reversed	O
to	O
return	O
the	O
ZX80	B-Operating_System
to	O
its	O
original	O
configuration	O
.	O
</s>
<s>
In	O
fact	O
,	O
the	O
only	O
real	O
change	O
made	O
in	O
most	O
markets	O
involved	O
the	O
video	O
output	O
frequency	O
(	O
the	O
ZX80	B-Operating_System
used	O
an	O
external	O
power	O
transformer	O
,	O
so	O
differences	O
in	O
AC	O
line	O
frequency	O
and	O
outlet	O
were	O
not	O
an	O
issue	O
to	O
the	O
machine	O
itself	O
)	O
.	O
</s>
<s>
The	O
ZX80	B-Operating_System
was	O
widely	O
advertised	O
as	O
the	O
first	O
personal	O
computer	O
for	O
under	O
£100	O
GBP	O
(	O
US$200	O
.	O
)	O
</s>
<s>
The	O
magazine	O
concluded	O
,	O
"	O
The	O
ZX-80	B-Operating_System
is	O
a	O
real	O
computer	O
and	O
an	O
excellent	O
value	O
"	O
,	O
but	O
only	O
for	O
beginners	O
who	O
could	O
learn	O
from	O
the	O
documentation	O
or	O
programmers	O
experienced	O
with	O
writing	O
Z-80	B-General_Concept
software	O
.	O
</s>
<s>
BYTE	B-Application
called	O
the	O
ZX80	B-Operating_System
a	O
"	O
remarkable	O
device	O
"	O
.	O
</s>
<s>
It	O
praised	O
the	O
real-time	O
,	O
interactive	O
BASIC	O
syntax	O
checking	O
,	O
and	O
reported	O
that	O
the	O
computer	O
performed	O
better	O
on	O
benchmarks	O
than	O
some	O
competitors	O
,	O
including	O
the	O
TRS-80	B-Device
Model	I-Device
I	I-Device
.	O
</s>
<s>
The	O
screen	O
blanking	O
during	O
program	O
execution	O
,	O
the	O
small	O
RAM	O
size	O
and	O
inadequate	O
built-in	O
Sinclair	B-Language
BASIC	I-Language
,	O
and	O
the	O
keyboard	O
received	O
criticism	O
,	O
and	O
the	O
review	O
recommended	O
against	O
buying	O
the	O
kit	O
version	O
of	O
the	O
computer	O
given	O
the	O
difficulty	O
of	O
assembly	O
and	O
because	O
purchasers	O
did	O
not	O
save	O
money	O
.	O
</s>
<s>
BYTE	B-Application
concluded	O
that	O
"	O
the	O
ZX80	B-Operating_System
might	O
be	O
summarized	O
as	O
a	O
high-performance	O
,	O
very	O
low-cost	O
,	O
portable	O
personal	O
computer	O
system	O
...	O
the	O
ZX80	B-Operating_System
is	O
a	O
good	O
starting	O
point	O
"	O
.	O
</s>
<s>
Sales	O
of	O
the	O
ZX80	B-Operating_System
reached	O
about	O
50	O
,	O
000	O
,	O
which	O
contributed	O
significantly	O
to	O
the	O
UK	O
leading	O
the	O
world	O
in	O
home	O
computer	O
ownership	O
through	O
the	O
1980s	O
.	O
</s>
<s>
There	O
were	O
also	O
clones	B-Device
of	I-Device
the	I-Device
ZX80	I-Device
,	O
such	O
as	O
the	O
MicroAce	O
,	O
and	O
from	O
Brazil	O
the	O
Nova	O
Eletrônica/Prológica	O
NE-Z80	O
and	O
the	O
Microdigital	O
TK80	O
.	O
</s>
