Re: MOSAIC and DECW$SCN_CLIPLIST_AREA message

From: JF Mezei (jfmezei.spamnot_at_teksavvy.com)
Date: 03/10/05 

Date: Thu, 10 Mar 2005 13:06:48 -0500

FredK wrote:
> On the VAX graphics, there was a lot of thought put into
> allowing the graphics hardware to clip the drawing output.
> This makes the drawing code much simpler, and much
> less CPU intensive - and the VAX was a weak CPU.

Interesting comment when you compare VMS/VAX with MVS/270 machines. The
370s were "weak" and couldn't handle character IO and instead made the
3270 terminals work "offline" to offload much of the IO from the CPU.
Meanwhile the VAX was able to support interactive terminals with
character io etc. So it is interesting that you would consider the VAX
as a "weak CPU".

(Of course by today's standards, it is a no-brainer).

> Also on many VAX graphics, offscreen memory was used
> for all kinds of things - the colormap, the cursor, clip lists,
> fonts, and importantly - pixmaps.

By offscreen memory, do you mean memory on the graphics card, or memory
attached to the CPU ?
Would VMS software have the ability to write to the memory in the SPX
card with DMA or whatever, or was all transfers done between VAX memory
and SPX memory through interrupts with the SPC card doing the transfer ?

> Most MIT derived servers also do not use offscreen memory
> for Pixmaps. Offscreen memory may be used for font

Ok, this is a question which may or may not be related, but has been
bugging me for some time.

What is a backing store in x-server terminology ?

> Probably something you don't care about, since it's just
> this one website.

Yeah, for now, it is just this one web site. but that page didn't seem
overly complex and anything which fills up a low file with close to a
1000 blocks of the same message is something which concerns me.

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