[Simh] Transferring the licence file to the VAX emulator

[Paul Koning]

> On Dec 18, 2018, at 9:20 PM, Larry Baker <baker at usgs.gov> wrote:
> 
> My 2¢ from the Way Back Machine:
> 
> I don't know what programmer's used before Fortran.  But, all these OS/360 features (and, likely earlier IBM OS's) were accessible from Fortran, the first commercially available high-level computer language.  Human input, including source code, was typically typed onto an 80-column card with a keypunch.  Such text "files" were read using 80 character "fixed-length" I/O.  Also, in those days, disk sectors were not fixed lengths.  Think of them as tiny strips of magnetic tape.  Just like tape, there is a physical record written and read by the hardware—what is now called a sector for fixed-length geometries—packed with embedded logical record(s) with a structure defined by software. ...
> 
> I don't recall when or why fixed-sector disks began to be required, and by which O/S's.  There would certainly have been a cost savings motive, both in the device electronics, and in the attachments, which could be much simpler than channel attachments.

"little strips of tape" is a good way to look at it.  I have the impression that this approach is specific to IBM.  Not that I know all the computer makers from that era.  But at least CDC had fixed size data-only sectors in the 6000 series, that would be around the same time as the IBM 360.  Those sectors didn't contain 8 bit bytes and weren't a power of two in length, but they were fixed.  In theory the disk controllers could create other formats (the controller had something like channel programs to parse the sector layout) but that wasn't used in practice.

Come to think of it, the IBM 1620 also had fixed length sectors (200 digits in the model 1311, if memory serves).

There are some other variants around: the EL-X8 had disks with per-track selectable sector size, from a list of 6 or so choices (non-power of two multiples of 27 words).

	paul