summary.txt

Elf/OS is a simple disk operating system for CDP1802 Elf-class computers.
It was initially released as version 0.1 back on June 29, 2004.  Since then
it has seen semi constant improvements for almost the last 20 years, with
the last release of 4.1.1 on April 26, 2022.  Since then health/age has
caused me to mostly retire from the 1802 scene, but that has not stopped
my work with the 1802.

At this point Elf/Os v5 is in final testing and will soon be released.  This
document summarizes the changes in Elf/OS v5.

  1. The directory walker has been decoupled from the file API.  Directory
     searches no longer rely on o_open and o_read for searching directores.
     Now directory searches occur on the raw sector data which greatly
     improves performance of diretory searches.

  2. The binary loader has also been decoupled from the file API.  Like
     the directory walker, the binary loader now reads data from the raw
     sectors, this vastly improves the performance of program loads.

  3. The file API o_read and o_write have been rewritten to improve
     performance.

  4. With the changes made to the directory walker and binary loader, 1k
     of internal buffer space was no longer needed, freeing up memory to
     provide native support for filesystem type II, with its 32-bit LAT it
     can now support disks larger than 268mb.  With the 32-bit LAT entries
     the full 28-bit sector addresses of IDE are now available to Elf/OS,
     allowing disks of up to 136gb to be usable by Elf/OS v5.

Elf/OS v5 is a nearly complete rewrite of the main kernel codebase. about 98%
of the code in the kernel is newly written.  The v5 kernel was first protoyped
in c and then hand converted to assembly language.  The c prototype will be
used to create a new version of disktool, which will be capable of working
on both type I and type II filesystems.  The old version of disktool will
not read type II filesystems.

Here is some performance comparisons between v4 and v5.  In both cases the
test was performed on a machine running with a 2mhz clock.  The time is
the time between pressing enter for the command to when the program first
starts to display outout on the terminal:

                                Seconds
   Program        Siz e         V4       V5
   LEM          16,805       20.76     1.20
   ZRUN3/Zork1   5,629       25.72     4.63
   PILOT/maze.p  6,280       23.66     6.70  maze.p size: 4,736
   RcBasicL2     6,823        9.09     0.67

In the above performance tests, the same disk image was used for both
tests, only the kernel being booted changed between the tests.

At this time there are no plans to make a conversion program to convert
type I filesystems to type II, so to use a type II filesystem you will 
need to build a new disk from scratch.  However, after I am done with
the initial release, I may revisit the idea of a converter.