<s>
The	O
Radio-86RK	B-Device
(	O
)	O
is	O
a	O
build-it-yourself	O
home	O
computer	O
designed	O
in	O
the	O
Soviet	O
Union	O
.	O
</s>
<s>
Design	O
of	O
the	O
computer	O
was	O
published	O
in	O
a	O
series	O
of	O
articles	O
describing	O
its	O
logical	O
structure	O
,	O
electrical	O
circuitry	O
,	O
drawings	O
of	O
printed	O
circuit	O
boards	O
and	O
firmware	B-Application
.	O
</s>
<s>
The	O
Radio-86RK	B-Device
is	O
the	O
successor	O
of	O
earlier	O
build-it-yourself	O
computer	O
of	O
the	O
same	O
designers	O
,	O
the	O
Micro-80	B-Device
,	O
and	O
has	O
limited	O
compatibility	O
with	O
it	O
.	O
</s>
<s>
Micro-80	B-Device
computers	O
were	O
assembled	O
by	O
only	O
a	O
few	O
enthusiasts	O
.	O
</s>
<s>
It	O
was	O
mostly	O
a	O
single	O
board	O
computer	O
,	O
as	O
the	O
second	O
board	O
served	O
only	O
as	O
the	O
base	O
to	O
mount	O
the	O
keyboard	B-Device
keys	O
.	O
</s>
<s>
The	O
main	O
board	O
used	O
a	O
single	O
large	O
connector	O
for	O
power	O
,	O
keyboard	B-Device
,	O
tape	O
recorder	O
and	O
even	O
video	O
output	O
.	O
</s>
<s>
Next	O
,	O
the	O
firmware	B-Application
has	O
to	O
be	O
written	O
in	O
two	O
erasable	B-General_Concept
ROM	I-General_Concept
chips	O
using	O
a	O
chip	B-General_Concept
programmer	I-General_Concept
.	O
</s>
<s>
Also	O
a	O
power	O
supply	O
unit	O
,	O
a	O
keyboard	B-Device
and	O
a	O
computer	O
case	O
were	O
to	O
be	O
made	O
.	O
</s>
<s>
The	O
circuitry	O
of	O
the	O
Radio-86RK	B-Device
contains	O
only	O
29	O
chips	O
and	O
was	O
relatively	O
easy	O
to	O
assemble	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
development	O
of	O
a	O
replacement	O
video	O
circuit	O
which	O
contained	O
19	O
chips	O
on	O
a	O
separate	O
board	O
,	O
and	O
was	O
similar	O
to	O
the	O
display	O
module	O
of	O
the	O
Micro-80	B-Device
computer	O
.	O
</s>
<s>
The	O
editorial	O
board	O
published	O
an	O
appeal	O
to	O
the	O
Soviet	O
electronics	O
industry	O
,	O
proposing	O
they	O
begin	O
producing	O
Radio-86RK	B-Device
kits	O
commercially	O
.	O
</s>
<s>
By	O
the	O
end	O
of	O
the	O
1980s	O
manufacturing	O
of	O
computer	O
cases	O
,	O
keyboards	B-Device
and	O
main	O
boards	O
for	O
the	O
Radio-86RK	B-Device
,	O
as	O
well	O
as	O
selling	O
electronic	O
components	O
were	O
carried	O
out	O
by	O
numerous	O
cooperatives	O
.	O
</s>
<s>
CPU	B-Device
:	O
KR580VM80A	O
(	O
Intel	B-General_Concept
8080A	I-General_Concept
clone	O
,	O
until	O
mid-1983	O
was	O
designated	O
as	O
KR580IK80A	O
)	O
clocked	O
at	O
1.777MHz	O
.	O
</s>
<s>
For	O
simplicity	O
's	O
sake	O
the	O
clock	O
generator	O
KR580GF24	O
(	O
Intel	O
8224	O
clone	O
)	O
is	O
used	O
both	O
for	O
CPU	B-Device
and	O
video	B-Device
controller	I-Device
.	O
</s>
<s>
As	O
16MHz	O
clock	O
generator	O
frequency	O
is	O
chosen	O
to	O
generate	O
television	O
compatible	O
signal	O
,	O
the	O
CPU	B-Device
is	O
unable	O
to	O
run	O
at	O
its	O
maximum	O
speed	O
of	O
2.5MHz	O
.	O
</s>
<s>
RAM	B-Architecture
:	O
16	O
KiB	O
in	O
original	O
version	O
,	O
using	O
K565RU3A	O
chips	O
(	O
4116	O
clone	O
)	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
double	O
memory	O
size	O
by	O
mounting	O
additional	O
RAM	B-Architecture
chips	I-Architecture
on	O
top	O
of	O
the	O
chips	O
installed	O
on	O
the	O
main	O
board	O
.	O
</s>
<s>
Video	B-Device
controller	I-Device
:	O
KR580VG75	O
programmable	O
CRT	B-Device
controller	O
,	O
interfaced	O
with	O
KR580VT57	O
(	O
Intel	B-Device
8257	I-Device
clone	O
)	O
DMA	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
The	O
DMA	B-General_Concept
controller	I-General_Concept
is	O
also	O
used	O
for	O
dynamic	O
memory	O
refresh	O
.	O
</s>
<s>
Video	B-Device
controller	I-Device
KR580VG75	O
is	O
a	O
clone	O
of	O
Intel	O
8275	O
,	O
a	O
rare	O
chip	O
not	O
used	O
in	O
any	O
mainstream	O
system	O
,	O
and	O
originally	O
proposed	O
for	O
terminals	O
.	O
</s>
<s>
Images	O
for	O
the	O
upper	O
case	O
Cyrillic	O
and	O
Latin	O
characters	O
in	O
KOI-7	O
N2	O
encoding	O
are	O
stored	O
in	O
the	O
KR573RF1	O
(	O
2708	O
clone	O
)	O
erasable	B-General_Concept
ROM	I-General_Concept
.	O
</s>
<s>
Semigraphics	B-Data_Structure
:	O
2	O
x	O
2	O
dot	O
matrix	O
combinations	O
in	O
the	O
graphic	O
character	O
subset	O
–	O
128	O
x	O
50	O
dots	O
total	O
.	O
</s>
<s>
Higher	O
resolutions	O
are	O
available	O
by	O
appropriate	O
video	B-Device
controller	I-Device
programming	O
.	O
</s>
<s>
Keyboard	B-Device
:	O
66	O
keys	O
.	O
</s>
<s>
The	O
keyboard	B-Device
matrix	O
is	O
attached	O
via	O
programmable	O
peripheral	O
interface	O
chip	O
KR580VV55	O
(	O
Intel	B-Device
8255	I-Device
clone	O
)	O
and	O
scanned	O
by	O
CPU	B-Device
.	O
</s>
<s>
Sound	O
:	O
CPU	B-Device
pin	O
INTE	O
used	O
as	O
a	O
sound	O
source	O
.	O
</s>
<s>
This	O
pin	O
is	O
usually	O
used	O
to	O
interface	O
with	O
programmable	B-Architecture
interrupt	I-Architecture
controller	I-Architecture
,	O
but	O
since	O
the	O
computer	O
did	O
not	O
have	O
any	O
interrupt	O
sources	O
,	O
the	O
pin	O
was	O
used	O
for	O
sound	O
generation	O
.	O
</s>
<s>
CPU	B-Device
commands	O
EI	O
and	O
DI	O
allowed	O
switching	O
the	O
pin	O
state	O
.	O
</s>
<s>
Storage	O
media	O
:	O
cassette	B-Device
tape	I-Device
.	O
</s>
<s>
With	O
DMA	B-General_Concept
controller	I-General_Concept
turned	O
on	O
the	O
CPU	B-Device
is	O
unable	O
to	O
measure	O
time	O
intervals	O
precisely	O
,	O
that	O
is	O
required	O
for	O
tape	O
reading	O
and	O
recording	O
.	O
</s>
<s>
Therefore	O
,	O
during	O
tape	O
operations	O
,	O
the	O
DMA	B-General_Concept
controller	I-General_Concept
turns	O
off	O
.	O
</s>
<s>
This	O
results	O
in	O
stopping	O
the	O
video	B-Device
controller	I-Device
and	O
memory	O
refresh	O
,	O
so	O
the	O
CPU	B-Device
performs	O
memory	O
refresh	O
programmatically	O
.	O
</s>
<s>
Signal	O
from	O
recorder	O
is	O
amplified	O
by	O
the	O
К140УД6	O
(	O
analog	O
of	O
MC1456	O
)	O
,	O
negative	O
part	O
is	O
cut	O
away	O
by	O
diode	O
and	O
then	O
the	O
signal	O
is	O
fed	O
to	O
the	O
dedicated	O
TTL	O
input	O
of	O
the	O
same	O
KR580VV55	O
that	O
serves	O
the	O
keyboard	B-Device
.	O
</s>
<s>
A	O
simple	O
second	O
layer	O
that	O
featured	O
leading	O
zeroes	O
,	O
offset	O
,	O
length	O
and	O
checksum	B-Algorithm
was	O
implemented	O
on	O
the	O
top	O
.	O
</s>
<s>
As	O
long	O
as	O
only	O
the	O
keyboard	B-Device
and	O
tape	O
recorder	O
are	O
required	O
,	O
this	O
second	O
chip	O
does	O
not	O
need	O
to	O
be	O
mounted	O
on	O
the	O
circuit	O
board	O
.	O
</s>
<s>
Two	O
or	O
four	O
of	O
them	O
are	O
dedicated	O
for	O
RAM	B-Architecture
(	O
so	O
16	O
or	O
32	O
Kb	O
)	O
,	O
one	O
for	O
ROM	B-Device
and	O
DMA	B-General_Concept
controller	I-General_Concept
(	O
during	O
write	O
operations	O
,	O
ROM	B-Device
is	O
disconnected	O
from	O
the	O
bus	O
,	O
and	O
data	O
is	O
transferred	O
to	O
the	O
DMA	B-General_Concept
controller	I-General_Concept
;	O
during	O
read	O
operations	O
,	O
DMA	B-General_Concept
controller	I-General_Concept
is	O
disconnected	O
from	O
the	O
bus	O
,	O
and	O
data	O
is	O
transferred	O
from	O
the	O
ROM	B-Device
)	O
,	O
one	O
for	O
video	B-Device
controller	I-Device
and	O
two	O
for	O
the	O
interface	O
chips	O
,	O
main	O
and	O
optional	O
.	O
</s>
<s>
Only	O
RAM	B-Architecture
actually	O
uses	O
all	O
available	O
addresses	O
,	O
IO	O
devices	O
only	O
use	O
a	O
few	O
cells	O
within	O
they	O
dedicated	O
8	O
Kb	O
segment	O
.	O
</s>
<s>
Separate	O
IO	O
commands	O
that	O
Intel	B-General_Concept
8080	I-General_Concept
has	O
are	O
not	O
supported	O
.	O
</s>
<s>
The	O
only	O
software	O
available	O
to	O
the	O
user	O
after	O
turning	O
on	O
the	O
computer	O
is	O
a	O
monitor	B-General_Concept
contained	O
in	O
ROM	B-Device
.	O
</s>
<s>
The	O
monitor	B-General_Concept
supports	O
basic	O
debugging	O
functions	O
,	O
it	O
allows	O
viewing	O
and	O
modifying	O
memory	O
cells	O
,	O
loading	O
and	O
saving	O
memory	O
contents	O
to	O
the	O
tape	O
,	O
entering	O
and	O
running	O
programs	O
in	O
binary	O
code	O
.	O
</s>
<s>
The	O
monitor	B-General_Concept
is	O
also	O
HAL	B-Operating_System
:	O
programs	O
that	O
access	O
the	O
hardware	O
only	O
by	O
calling	O
the	O
monitor	B-General_Concept
library	O
support	O
both	O
16Kb	O
and	O
32	O
Kb	O
RAM	B-Architecture
versions	O
and	O
often	O
also	O
Micro-80	B-Device
predecessor	O
.	O
</s>
<s>
Initially	O
,	O
the	O
Radio	O
magazine	O
distributed	O
programs	O
for	O
the	O
Radio-86RK	B-Device
in	O
the	O
form	O
of	O
hexadecimal	O
dumps	O
.	O
</s>
<s>
It	O
was	O
easy	O
to	O
make	O
a	O
mistake	O
when	O
typing	O
in	O
large	O
dumps	O
,	O
so	O
the	O
magazine	O
published	O
checksums	B-Algorithm
along	O
with	O
the	O
dumps	O
.	O
</s>
<s>
It	O
was	O
necessary	O
to	O
execute	O
"	O
O	O
"	O
monitor	B-General_Concept
directive	O
to	O
calculate	O
the	O
checksum	B-Algorithm
.	O
</s>
<s>
The	O
magazine	O
published	O
two	O
versions	O
of	O
the	O
BASIC	O
interpreter	O
:	O
an	O
adapted	O
version	O
of	O
Micro-80	B-Device
BASIC	O
and	O
a	O
version	O
specially	O
developed	O
for	O
the	O
Radio-86RK	B-Device
featuring	O
enhanced	O
editing	O
capabilities	O
,	O
new	O
functions	O
,	O
and	O
other	O
improvements	O
.	O
</s>
<s>
Other	O
software	O
published	O
in	O
the	O
magazine	O
included	O
assembler	O
,	O
debugger	B-Application
,	O
disassembler	O
,	O
text	B-Application
editor	I-Application
,	O
voice	O
recorder	O
,	O
music	O
editing	O
system	O
.	O
</s>
<s>
Another	O
way	O
of	O
obtaining	O
software	O
was	O
the	O
tape	O
exchange	O
among	O
Radio-86RK	B-Device
owners	O
.	O
</s>
<s>
From	O
that	O
moment	O
it	O
became	O
possible	O
to	O
buy	O
software	O
for	O
the	O
Radio-86RK	B-Device
.	O
</s>
<s>
In	O
1989	O
the	O
RAMDOS	O
operating	B-General_Concept
system	I-General_Concept
was	O
developed	O
for	O
the	O
computer	O
.	O
</s>
<s>
It	O
uses	O
part	O
of	O
computer	O
's	O
RAM	B-Architecture
as	O
a	O
RAM	B-Application
drive	I-Application
.	O
</s>
<s>
The	O
contents	O
of	O
RAM	B-Application
drive	I-Application
can	O
be	O
loaded	O
and	O
saved	O
to	O
the	O
tape	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
has	O
a	O
minimalistic	O
user	O
interface	O
with	O
only	O
seven	O
commands	O
;	O
it	O
also	O
adds	O
support	O
for	O
file	O
operations	O
to	O
the	O
BASIC	O
interpreter	O
.	O
</s>
<s>
In	O
October	O
1992	O
,	O
the	O
Radio	O
magazine	O
and	O
TOO	O
Lianozovo	O
company	O
announced	O
a	O
floppy-disk	B-Device
controller	I-Device
for	O
the	O
Radio-86RK	B-Device
and	O
the	O
Microsha	O
.	O
</s>
<s>
The	O
disk	O
operating	B-General_Concept
system	I-General_Concept
(	O
DOS	O
)	O
was	O
stored	O
in	O
erasable	B-General_Concept
ROM	I-General_Concept
on	O
the	O
controller	O
board	O
.	O
</s>
<s>
The	O
Radio	O
magazine	O
published	O
only	O
the	O
electrical	O
circuitry	O
of	O
the	O
controller	O
but	O
not	O
the	O
firmware	B-Application
.	O
</s>
<s>
Radio-86RK	B-Device
owners	O
were	O
invited	O
to	O
buy	O
the	O
fully	O
assembled	O
controller	O
or	O
a	O
kit	O
along	O
with	O
two	O
floppy	O
disks	O
containing	O
external	O
DOS	O
commands	O
,	O
programming	O
languages	O
and	O
text	O
description	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
first	O
industrially	O
produced	O
version	O
of	O
the	O
Radio-86RK	B-Device
was	O
the	O
computer	O
named	O
Microsha	O
(	O
an	O
abbreviation	O
for	O
the	O
words	O
Microcomputer	O
and	O
School	O
)	O
.	O
</s>
<s>
Initially	O
,	O
the	O
authors	O
had	O
given	O
that	O
name	O
to	O
the	O
original	O
computer	O
,	O
but	O
the	O
editorial	O
board	O
has	O
changed	O
the	O
name	O
to	O
Radio-86RK	B-Device
.	O
</s>
<s>
Eventually	O
,	O
the	O
name	O
Microsha	O
was	O
given	O
to	O
the	O
industrially	O
produced	O
version	O
of	O
Radio-86RK	B-Device
.	O
</s>
<s>
Microsha	O
preparation	O
for	O
serial	O
production	O
went	O
in	O
parallel	O
with	O
Radio-86RK	B-Device
articles	O
publication	O
.	O
</s>
<s>
The	O
changes	O
authors	O
made	O
to	O
the	O
design	O
and	O
firmware	B-Application
made	O
Microsha	O
incompatible	O
with	O
Radio-86RK	B-Device
.	O
</s>
<s>
In	O
1989	O
,	O
the	O
Radio	O
magazine	O
had	O
published	O
new	O
firmware	B-Application
for	O
Microsha	O
that	O
improved	O
software	O
compatibility	O
.	O
</s>
<s>
Following	O
magazine	O
publication	O
,	O
a	O
number	O
of	O
factories	O
started	O
industrial	O
production	O
of	O
several	O
home	O
computer	O
models	O
using	O
the	O
Radio-86RK	B-Device
design	O
.	O
</s>
<s>
Not	O
all	O
models	O
were	O
fully	O
compatible	O
with	O
Radio-86RK	B-Device
and	O
included	O
different	O
improvements	O
,	O
such	O
as	O
expanded	O
memory	O
size	O
,	O
additional	O
character	O
sets	O
,	O
rudimentary	O
color	O
support	O
.	O
</s>
<s>
The	O
technical	O
capabilities	O
of	O
the	O
Radio-86RK	B-Device
were	O
very	O
modest	O
.	O
</s>
<s>
The	O
RAM	B-Architecture
expansion	O
was	O
impossible	O
without	O
serious	O
modifications	O
and	O
loss	O
of	O
compatibility	O
.	O
</s>
<s>
Although	O
the	O
designers	O
of	O
the	O
Radio-86RK	B-Device
had	O
developed	O
a	O
new	O
16-bit	O
computer	O
,	O
the	O
Micro-16	O
(	O
based	O
on	O
the	O
K1810VM86	B-Device
microprocessor	O
,	O
with	O
a	O
CGA-compatible	O
graphics	O
mode	O
that	O
was	O
capable	O
of	O
running	O
software	O
for	O
the	O
CP/M	B-Operating_System
-86	I-Operating_System
and	O
MS-DOS	B-Application
)	O
,	O
the	O
editorial	O
board	O
again	O
opted	O
for	O
a	O
computer	O
based	O
on	O
the	O
8-bit	O
processor	O
KR580VM80	O
.	O
</s>
<s>
The	O
publication	O
of	O
articles	O
on	O
the	O
new	O
computer	O
Orion-128	B-Device
began	O
in	O
January	O
1990	O
.	O
</s>
