Hardware
The machine was based on a powerful (for the time) 16-bit single-chip K1801VM1 CPU, clocked generally at 3 MHz. It was almost perfectly compatible with Digital Equipment Corporation's LSI-11 line, though it lacked EIS and further command set extensions. The manufacturer also closely copied the PDP-11's internal architecture. Each model had one free card slot which was electrically, but not mechanically, compatible with Q-Bus. The first versions had 32 KB onboard DRAM, half of which was used as video memory. That was extended to 128 KB in later models, with video memory extended to two 16 KB pages.
Video output on all models was provided by the K1801VP1-037 VDC, a rather spartan chip. It was actually a standard 600-gate ULA with a VDC program that allowed for two graphic video modes, high-res (512x256, monochrome) and low-res (256x256, 4 colors), and supported hardware vertical scrolling. Later models had 16 hardwired 4-color sets selectable from 64 color palette. It didn't support text modes, but simulated two via BIOS routines: 32x25 and 64x25. Some operating systems such as ANDOS managed to output text in 80x25 mode when displaying documents imported from IBM PC, by placing characters more densely. Output was through two separate 5-pin DIN connectors for a monochrome TV or color TV/monitor. Sound on all models was initially through a simple programmable counter connected to an onboard piezo speaker. Later, the General Instrument AY-3-8910 became a popular aftermarket addition.
All models also had a 16-bit universal parallel port with separate input and output buses for connecting peripherals such as printers (Eastern Bloc printers used the incompatible ИРПР interface instead of the more popular Centronics port, so Centronics printers needed an adapter), mice or Covox DACs for sound output, and tape recorder port for data storage. Later models included a manufacturer-supplied floppy drive controller (that could be plugged into a Q-Bus slot) by default. It was available for earlier models as an aftermarket part, but homebrew ones (that also often extended rather anemic 16K memory of original BK) were more popular. A cottage industry for such peripherals and mods flourished.
Read more about this topic: Electronika BK
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