80-Bus News


January–March 1982 · Volume 1 · Issue 1

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A review by Stuart Wood

Polydos is designed as a disk operating system for a Nascom with either Nas-Sys 1 or 3 monitors, Nascom ROM BASIC and ideally 48k of RAM. If the full 48k is not fitted then 4k must be fitted at address C000 hex as this is Polydos’s workspace area. Two types of disk hardware are supported, namely the Gemini G805 (single density) and Gemini G809/G815 (single or double density) disk drive units. The type of disk unit must be specified when Polydos is ordered since the actual disk driver routines are different. The package as supplied contains two 2708 type EPROMs which contain the bootstrap routines, the package also contains a serialised distribution copy of the operating system itself and one very thick manual! The EPROMs are located at address D000 hex and fitting instructions are given in detail. Don’t worry if you have ZEAP in EPROM at this address because you can throw it (or give it) away! Incidently, if you have Naspen or Programmer’s aid, you will probably find these also residing in the depths of your dustbin before long. What is the reason for this madness? Very simple really, along with the disk operating system itself is an excellent disk based assembler, an enhanced BASIC and a disk based text editor along with a few other goodies! The package is divided into several major sections which are as follows–

Exec.   This is an overlay file which is loaded into the overlay area at C800H to CFFFH. This program handles the command lines which prompt the user with a ‘$’ in the first character position in the line. If the ‘$’ is backspaced over, normal Nas-Sys commands are available with the exception of the ‘S’ and ‘B’ commands. An ‘E0’ command will restore normal operation on these commands. The Exec file contains the code for most of the commands available including: DIR – directory, upto 50 entries with options for statistical data and directory to printer; DEL and UNDEL – allow files to be deleted, and recovered if accidentally deleted; SAVE and LOAD – normally used to manipulate machine code files without execution, an optional load address can be specified; LIST and SKIP – printer control commands for hardcopy of files or list to display; READ and WRITE – direct sector versions of LOAD and SAVE; NEW – tells Polydos you have replaced a disk since directory is held in RAM and must be updated; BOOT – allows complete reboot of system.

Dfun   This is another overlay file which handles the following commands: COPY – disk to disk copy and allows single disk copying; REN – rename files; LOCK and UNLOCK – prohibits file deletion or listing in the normal form of the DIR command; ATTRIB – redefine load and execution addresses of files; PACK – removes deleted files and re-packs disk; NAME – give a disk a new name; BUFFER – redefine start and length of RAM buffer used in PACK, COPY and LIST commands.

Emsg   This overlay is invoked everytime a system error occurs to print the error message.

Info   This file is loaded on boot up (if present) otherwise default parameters are substituted into the information file area at C200H to C2FFH. The file contains parameters relating to the cursor including blink rate and character type and also to the printer including initialisation string and low level driver.

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