Ultra-Tiny Circle M MinZ-C Packs a Fully-Functional High-Spec CP/M System Into a Tiny Footprint

Measuring just 2"x2", this tiny single-board computer comes packed with 7.5GB of CP/M software and documentation.

Gareth Halfacree
3 years agoRetro Tech

Canadian vintage computing specialist Circle M Systems has released what could well be the smallest cased single-board computer to be based around a Zilog Z180 processor — the MinZ-C, or Minimum Z180 Cased.

"The primary objective was to build a small, fast, and reliable encased Z180 system running CP/M 2.2 which could also be easily upgraded to use CP/M 3 or other similar operating systems," Circle M explains. "Having built several variations of Z180 systems, this one uses the basic features that I've found to be most useful. It's architecture is pretty classic using a processor with integrated I/O, SRAM, flash memory instead of EPROM and a CPLD for the glue logic."

The system is built around a Zilog Z8S180 processor, a modern equivalent to the classic Z80 which powered a range of popular eight-bit computing systems. To this, Circle M has added 512kB or 1MB of zero-wait static RAM (SRAM) with support for a 438kB or 948kB of RAM disk, 512kB of flash for boot code, the CP/M 2.2 operating system, and a 496kB ROM disk, 256 bytes of EEPROM, and 64 bytes of battery-backed SRAM.

The design also includes two USB ports, a microSD socket with a 25MHz SPI interface, a real-time clock (RTC) with rechargeable battery, status LED, user-programmable LED, an optional 2Hz heartbeat LED, and a physical reset button — all in a translucent plastic case measuring just 2x2x0.6in. The package also includes a 16GB microSD with 8MB CP/M partition, source code for the BIOS and operating system, and around 7.5GB of period-appropriate software and documentation.

"It can be used as-is or as a development/testing platform for software such as applications and/or operating systems (i.e. ZCPR, CP/M-3, MP/M, etc.)," Circle M writes. "After initialization, this system runs with ZERO memory wait states since each wait state would result in approximately a 25 per cent reduction in effective speed."

The tiny board is available fully-assembled on the Circle M Tindie store, priced at $80 for 512kB and $90 for 1MB versions in 33.333MHz stock and 36.864MHz overclocked variants.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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