20 Jun
2018
20 Jun
'18
2:10 p.m.
On Tuesday, 19 June 2018 at 23:41:41 -0600, Warner Losh wrote:
On Tue, Jun 19, 2018 at 11:04 PM, Peter Jeremy
<peter(a)rulingia.com> wrote:
Looking at something like the IBM 370 series (mid-1970s), I/O was
performed by the channels, effectively separate processors with a very
limited instruction set. Others, like the UNIVAC 1100 series, could
perform I/O directly or via separate processors. This was similar on
the /360, but very different on the 1401.
In each case, from my recollection, main memory and the peripheral
were the bottleneck. For the UNIVAC 1108 (1965, the one of which I
have the best recollection), memory was 36 bits every 750 ns, and you
could expect it to be interleaved at least 2 ways, so you could
transfer data across two channels to a FH 432 drum at in the order of
2.5 MW/s. This could lead to underruns depending on what else was
going on in the system. Other peripherals were slower, so this would
have been about the maximum.
Greg
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On 2018-Jun-20 08:55:05 +1000, David Arnold
<davida(a)pobox.com> wrote:
So what could an old mainframe do as far as I/O was concerned? Google
didn't provide me a straight forward answer... Does the screen count as I/O?
I was thinking about that as well. 1080p30 video is around 2MBps
as H.264 or about 140MBps as 6bpp raw. The former is negligible,
the latter is still shy of the disparity in CPU power, especially
if you take into account the GPU power needed to do the decoding.
I???d suggest that it???s just that the balance
is (intentionally) quite
different. If you squint right, a GPU could look like a
channelized I/O
controller.
I agree. Even back then, there was a difference between
commercial-oriented mainframes (the 1401 and 360/50 lineage - which
stressed lots of I/O) and the scientific mainframes (709x, 360/85 -
which stressed arithmetic capabilities).