29 May
2018
29 May
'18
11:10 p.m.
On 5/28/18, Noel Chiappa <jnc(a)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.