[TUHS] Control-T (was top)

[Paul Winalski]

On 5/28/18, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>
> The thing that killed an OS was the fact that output was programmed I/O, a
> character at a time; using interrupt-driven operation, it took an interrupt
> per character.
>
> The DH11 used DMA for output, and was much easier on the machine.

Yes, I meant output.  Thanks for refreshing my hazy memory.  I found
the TU58 technical manual online.  It turns out that the TU58 did have
a data buffer, but it's only 128 bytes, so transferring each 512-byte
block required multiple messages and interrupts, and that introduces
the overrun/underrun problems.

Most large VAX timesharing systems used the DH11.

-Paul W.