From mboxrd@z Thu Jan 1 00:00:00 1970 From: paul.winalski@gmail.com (Paul Winalski) Date: Tue, 29 May 2018 13:10:15 -0400 Subject: [TUHS] Control-T (was top) In-Reply-To: <20180529025511.C6E0318C08A@mercury.lcs.mit.edu> References: <20180529025511.C6E0318C08A@mercury.lcs.mit.edu> Message-ID: On 5/28/18, Noel Chiappa 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.