A Tribute to the Dick Smith System 80
(aka Video Genie and PMC-80/81)

OS 80

OS 80 was actually Percom's MicroDos (Version 1) re-branded for the Dick Smith offering.  The manual is exactly the same as the MicroDos one with the exception of the front page.  If you want to see what this tiny(!) DOS was like you can downloaded it here, and check it out on one of the emulators

The text below shows a review, taken from the Australian-produced magazine Micro-80. Issue, 16 (March 1981) page 7.

PERCOM OS-8O DISK OPERATING SYSTEM - Reviewed by Michael Cooper

The Percom Disk Operating System 0S-80 is a memory efficient, high speed program which extends Level 2 BASIC to permit Disk Drive control. The DOS occupies 7K of low user RAM, and provides all the necessary commands to enable the user to write programs using Disk BASIC. Due to its small size OS-80 enables a 16K single disk system to be both viable and useful.

To compact the DOS as much as possible it contains no file handling routines or directory track. Instead a type of disk mapping is used. This technique enables the user to specify the drive (0 - 3) and sector (0 - 399 on a 40 track drive) as a 5 digit integer. The first digit specifies the drive, the next digit is always 0 and the last three digits specify the sector. For example, if you wished to save a BASIC program to Disk Drive 1, starting at sector 125, the command would be SAVE 10125. The OS-80 system would then save the program and finally display the number of the last sector used. To load the same program into your "80" you command LOAD 10125 (,R). This would cause the loading of the BASIC program stored on the disk in Drive 1, starting at sector 125. The (,R) is optional, but if included causes the program to be loaded then RUN. The OS-80 system also includes a MERGE command to allow a program on disk to be merged with one in memory.

The 0S-80 has a number of system commands, all using the CMD verb to perform the various functions.

CMD"F",D is used to format the disk in drive D. CMD"M",D dumps a core image of DOS onto drive 0, sectors 0 - 19. CMD"K",D combines the above two commands CMD"H",A$ allows the user to input a text string of up to 128 characters, which appears during the booting of DOS CMD"K",A$ allows for a chaining mode, so that BASIC programs can be loaded and executed from the boot.

OS-8O also has 3 disk I/O statements to enable the processing of data stored on disk. GET reads the specified disk sector either into a buffer or into a string variable depending on the command syntax, whilst PUT writes either a string variable or the contents of a buffer to the specified sector. For example, PUT 25,A$ will save the contents of A$ to sector 25 on drive 0 (please note that users with a single drive only have to specify the sector). GET #l,IX% will read the sector and drive specified by the value of variable IX%, into I/O buffer number one. Unlike TRS-DOS the number of buffers is fixed at 4. However I have never needed to use any more than that in the most complex program. Having got the data into buffer 1, the user can FIELD it up into records as in TRS-DOS Disk BASIC.

By using the DOS Vector Table in ROM, the OS-8O system links into Level 2 and implements most of the TRS-DOS Disk Basic conversion and placement functions, usually with identical syntax. Included are LSET, RSET, MKI$, MKS$, MKD$, CVI, CVS, CVD, INSTR, MID$, DEF FN, DEFUSER and LINEINPUT

Hexadecimal constants can also be used for all arguments, but not Octal. OS-8O allows the user to easily tailor the DOS to the system requirements. To change the number of tacks OS-8O will process, just POKE the number into location 17554. To change the track to track stepping time, POKE the value into 17556. The OS-8O system disk supplied is set for Pertec drives as supplied by Dick Smith (40 tracks with 20 millisecond steps).

I would recommend OS-8O for both beginners to disks and the seasoned programmer as it offers both simplicity and versatility. The system disk is supplied with utility programs to perform simple file handling, a program of disk utilities such as FORMAT, BACKUP, COPY, FREE, VERIFY, DUMP and ERASE and a program called "The 5 1/4 inch notebook" which is a simple data manager. Unfortunately, disks are not compatible with those made under TRS-DOS as OS-8O has no Directory track but except for minor syntax variations, most TRS-DOS Disk Basic programs will run under OS-SO. The reward for users converting TRS-DOS Disk BASIC programs is faster disk I/O and no potential for disks with "zapped and unusable" directories. The major job in the conversion is the removal of all the OPEN and CLOSE verbs and modification of file record logic to encompass 0S-80 sector read/writes.

If you haven't a copy of OS-SO then I strongly urge you to buy one and use it. You will find it faster than either TRS-DOS or NEWDOS-SO and for the novice, much simpler to use. The only drawback it suffers is its limitation to BASIC program and data storage, but at the price, it is one of the true software bargains.

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