HDOS

from Wikipedia, the free encyclopedia
HDOS
developer Gordon Letwin
License (s) proprietary , later public domain
Current  version 3.02
Architecture (s) Heathkit H8 , Heathkit H89
timeline Ver. 1.0
Ver. 1.5
Ver. 1.6
Ver. 2.0
ver. 3.0
Ver. 3.02
Languages) English
Others Development stopped

HDOS or HeathDOS is an early operating system from the Heathkit company .

Gordon Letwin , who later was the leading developer and chief architect of the OS / 2 operating system at Microsoft , developed the operating system from 1978. Originally, the software was implemented for the Heathkit H8 , but can also run without changes on the H89, which was later released . Initially, only a few system programs such as assembler were available for HDOS . In the course of time, additional software was developed by third-party manufacturers. Even games such as an implementation of Space Invaders and Pac-Man - clone Munchkin created. In addition, the programming languages BASIC , COBOL and FORTRAN were implemented for HDOS.

In 1983 a license for HDOS was around $ 150. The printed source text could be purchased for a surcharge of around US $ 200 .

technical description

Memory allocation of HDOS

HDOS is an 8-bit operating system for single-user operation.

Device driver

HDOS was - in contrast to the widespread operating system CP / M - from version 2.0 onwards, one of the first operating systems to use reloadable device drivers in order to achieve a certain degree of device independence and expandability. A device driver consists of a file with the name XX.dvd, where XX stands for the specific abbreviation of the respective device. Using the SET command, a device driver can be loaded into the memory and configured using various parameters.

Memory management

With its 8-bit data bus , the H89's Z80 processor can address a total of 64 kB of memory. The bottom 8 kB contains the ROM , which contains the routines for booting and parts of the management routines for the floppy disk drives. The actual RAM area begins at address 2000hex. Between this address and address 27FFhex, HDOS reserves an area for various system parameters and system tables as well as for the program stack . The area of ​​the memory that can be used for applications begins at address 2280hex and extends to address D732hex. The area from address EB56hex is reserved by the operating system, with an area reserved for the additional device drivers between this address and address EDAFhex.

The highest memory block between EDB0hex and FFFFhex contains the memory- resident part of the system with all system routines such as interrupt handling and the device drivers for the connected floppy drives.

The area between D733hex and EB55hex is a so-called overlay area . This is where the operating system stores routines that are not required constantly and are only loaded into memory when required. If this memory area is occupied by an application that accesses these routines, it is temporarily stored on a floppy disk. The system routines are then stored in the area and the system call is executed. As soon as the system call has ended, the relocated program parts are reloaded from the diskette back into the memory.

Files

The operating system is divided into four areas:

  • the command interpreter. It is contained in the SYSCMD.SYS file.
  • the in-memory part of the system.
  • the two parts for the overlay area.
  • the device drivers.

The memory-resident part and the overlay parts are contained in the HDOS.SYS file.

Supplied software

A line-oriented text editor , an assembler and the BASIC variant Extended Benton Harbor BASIC were delivered together with HDOS . The assembler offered the possibility - unusual for this time - of storing parts of the source text in separate files and, if necessary, including them in the source text using instructions.

Version history

The official publications are the versions 1.0 (published 1980), 1.5, 1.6, 2.0, 3.0 and 3.02. The first four versions were written by Gordon Letwin. William G. Parrott, David T. Carroll, Dale L. Wilson and Richard Musgrave developed version 3.0 and after Parrott, Carroll and Wilson left, Richard Musgrave expanded the system to the last version 3.02. On July 19, 1989, version 2.0 was released as public domain by Jim Buszkiewicz, managing editor of the Heathkit Users Group .

Individual evidence

  1. ^ Advertisement by a Californian software vendor in the Silicon Gulch Gazette from September 1981 (PDF; 4.15 MB), accessed on December 15, 2008
  2. ↑ a b c d e f g Michael A. Pechura: Comparing Two Microcomputer Operating Systems , Article in Communications of the ACM, March 1983 (PDF) , accessed December 15, 2008
  3. ↑ a b Software Reference Manual for HDOS Disk Operating System , Heathkit 1990