What is "piece of glass"?
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Some programs make a reference to "piece of glass". It's related to the display system.
I got this from Bruce Baumgart:
POG Piece-of-Glass was the name for a buffer of vectors and text ( for the Triple-I display ) that could be independently shown or hidden, but was ready to be displayed. The GLASS buffers were passed to the Time Sharing System using the DPYOUT ( same as UPGIOT, Update Glass I/O Transfer )
So that smooth animation was possible, for example
https://www.saildart.org/allow/arm.gifThe POG buffers resided in the System Free storage space, AFTER being copied and relocated from the user address space ( users might get swapped out )
Each user was allowed 16 decimal POG buffers.
The Glass UUO was UPGIOT ( opcode == 0703 ) and is documented in section 4 or the UUO manual ( around page #65 )
A fancy display of the UUO manual with page turning is viewable at the Internet Archive at URL
https://archive.org/details/uuomanual00brucrichgo to page #65 to read about the UPGIOT and its Glass buffers
a PDF of the manual that was scanned is at URL
https://www.saildart.org/allow/pdf/uuomanual00brucrichThe many versions of that manual over the years have filename UUO with various extensions and are found in public areas such as [S,DOC] and [CSP,DOC] on the SAIL DART dot ORG for example:
https://www.saildart.org/UUO.ME[S,DOC]2
is a version dated 1975-07-29.
The Les Earnest claim that “Glass” were the foundation of “Windows” I consider an over reach. The “windows” idea was common in computer graphics in that period of the 1970s and was indeed better implemented at Xerox PARC and SRI, our Stanford “Glass” was quite early like 1967 and 1968, and very primitive.