The machine is based on a 16-bit single-chip
K1801VM1 CPU, clocked generally at 3 MHz. It is compatible with
Digital Equipment Corporation's LSI-11 line, though it lacks
Extended Instruction Set (EIS) and further instruction set extensions. The manufacturer also closely copied the PDP-11's internal architecture. Each model has one free card slot which is electrically, but not mechanically, compatible with
Q-Bus. The first version features 32 KiB onboard DRAM, half of which is
video memory. That is extended to 128 KiB in later models, with video memory extended to two 16 KiB pages. Video output on all models is provided by the K1801VP1-037
VDC, a rather spartan chip. It is a standard 600
gate array, or
uncommitted logic array (ULA), with a VDC program that allows for two graphic video modes, high-resolution (512×256, monochrome) and low-resolution (256×256, 4 colors), and supports hardware vertical
scrolling. Later models have 16 hardwired 4-color sets selectable from 64 color
palette. It does not support text modes, but simulates two via
BIOS routines: 32×25 and 64×25. Some operating systems such as ANDOS have managed to output text in 80×25 mode when displaying documents imported from IBM PC, by placing characters more densely. Output is through two separate 5-pin
DIN connectors for a monochrome TV or color TV/monitor. Sound on all models is initially through a simple programmable counter connected to an onboard
piezo speaker. The
General Instrument AY-3-8910 is a popular aftermarket addition. All models also have a 16-bit universal
parallel port with separate input and output buses for connecting peripherals such as
printers (
Eastern Bloc printers used the incompatible
IFSP () interface instead of the
IEEE 1284 (Centronics) port, so Centronics printers need an adapter),
mouse or
Covox digital-to-analog converters (DACs) for sound output, and
tape recorder port for data storage. Later models include a manufacturer-supplied
floppy drive controller by default, that can be plugged into a Q-Bus slot. It is available for earlier models as an aftermarket part, but homebrew ones that also often extends 16 KiB memory of original BK are more popular.
Versions BK-0010 The is the first model, originally released in 1983, serial production started in 1985. It has a pseudo-
membrane keyboard (an array of mechanical microswitches without keycaps, covered by flexible overlay), 32
KiB RAM, 8 KiB ROM with BIOS (chip K1801RE2-017), 8 KiB ROM with
FOCAL interpreter (K1801RE2-018), 8 KiB ROM with debugger (K1801RE2-019) and one free ROM slot. Its CPU is clocked at 3 MHz. A
tape recorder is used for data storage in the factory configuration. This model was criticized for its uncomfortable keyboard – while
mechanical in nature, lack of keycaps lead to the same unsatisfactory tactile response, that was seen as unacceptable when the machine was used in home or educational settings, although such keyboard could be easily sealed fully, so this version found wide use as an
industrial controller. Other points of criticism included the FOCAL programming language supplied by default instead of the more common BASIC and the lack of peripherals and software. While all hardware was well-documented and easy to work with, the machine was delivered with no programming tools.
BK-0010.01 The follow-up version,
БК-0010.01 (sometimes referred to as -0010-01), is essentially the same machine, but with a conventional full-travel keyboard and a
Vilnius BASIC p-code compiler in the ROM, correcting the weakest points of its predecessor. While the BASIC dialect used is powerful and well-optimized (it is a scaled-down clone of
MSX BASIC), the keyboard still has shortcomings. While it is much more comfortable to work with, the keys were prone to sticking, significant
bounce and wore quickly, though a model with a further improved keyboard became available later. The FOCAL interpreter was not dropped but instead shipped on an external
ROM cartridge that can be inserted into the Q-Bus slot.
BK-0010Sh is a model intended for school use. It can be either the −0010 or −0010.01 model but includes a special
current loop network adapter rated at 19200
bits per second (bit/s), which can be inserted into the
Q-Bus slot. Based on ULA chip K1801VP1-035, and later on K1801VP1-065, the adapter is compatible with
Digital Equipment Corporation (DEC) DL-11 and KL-11 serial interfaces, but without modem control bits. It includes a monitor, usually a modified Yunost' compact TV for school settings.
BK-0011 BK-0011 was released in 1989. It has 128 KiB of RAM divided into 16 KiB pages. Its CPU is clocked at 4 MHz by default. It includes a newer version of BASIC in ROM and 16 selectable video palettes, which were almost universally criticized by users for their odd color combinations. It has a floppy controller, with the drive available as an add-on.
BK-0011M Some changes in the BK-0011, while minor, made it incompatible with earlier -0010 models. It cannot load 0010 programs from a cassette tape. Even if it could have loaded them, crucial subsystems, such as sound, are still incompatible. The manufacturer redesigned the machine, restoring compatibility with earlier models. The resulting model, the BK-0011M, quickly went into production, and most BK-0011 series computers are actually BK-0011Ms. Since the modifications were minor, most of the handful of -0011 models that made it to market have been upgraded to -0011M models by enthusiasts.
Mods It is not uncommon among owners to install one or two mechanical
switches that made using the computer more convenient. Some of the common mods were: •
Reset push-button.
Programs often
hang. Also, some
games do not have a properly implemented Exit function. Without this button, the computer has to be reset by
power cycling, which eventually leads to a worn out power switch on the external power supply. The reset interrupt can be caught by the operating system, so under such systems (for example,
ANDOS,
MK-DOS), the reset button exits to the OS's
file manager. •
Pause switch. This switch activates hardware suspension of
instruction execution in the processor. The pause switch is useful for pausing games, most of which do not have a
pause key. A few games, however, do not behave gracefully after being returned from suspension, because the programmable hardware
timer built into the processor
chip is still running while the instruction execution was suspended. The BK also has a software key combination for pause. •
Clock speed switch (
turbo switch). This changes the processor
clock speed from the standard 3 MHz (BK-0010* series) to 4 or 6 MHz, or from the standard 4 MHz (BK-0011* series) to 3 or 6 MHz. Not all processor samples work reliably at 6 MHz; the possibility of such
overclocking has to be determined experimentally for each sample. Switching the clock speed changes the pace of dynamic games. The turbo switch usually has to be installed together with the pause switch, because the simplest circuit for switching the clock speed produces bad
waveform shapes in the clock signal due to
contact bounce in the mechanical switch, running the risk of hanging the software execution unless the processor is in the suspended state. •
Sound on/off switch, or
sound volume knob, which adjusts the
volume level of the internal
piezoelectric speaker using a
potentiometer. At this same time as adding this, the modder can replace the speaker with a louder one. Enthusiasts also manage to connect more advanced devices to BK series computers: they developed a
hard disk drive (HDD) controller, and 2.5" HDDs have been successfully used with BK computers. Other popular enhancements are
AY-3-8912 sound chips and
Covox Speech Thing. ==Emulators==