On Tuesday, 19 June 2018 at 23:41:41 -0600, Warner Losh wrote: > On Tue, Jun 19, 2018 at 11:04 PM, Peter Jeremy wrote: > >> On 2018-Jun-20 08:55:05 +1000, David Arnold wrote: >>> 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). > > So what could an old mainframe do as far as I/O was concerned? Google > didn't provide me a straight forward answer... 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 -- Sent from my desktop computer. Finger grog@lemis.com for PGP public key. See complete headers for address and phone numbers. This message is digitally signed. If your Microsoft mail program reports problems, please read http://lemis.com/broken-MUA