On 2017-08-04 14:54, Noel Chiappa via cctalk wrote:
> From: Warner Losh
> had problems finding out just how fast Q-Bus can go
Something like 700 nsec for a cycle (best case), so assuming 16-bit
transfers, a max of a little over 20 Mbit/sec.
From an old email from tim Shoppa who tested some QBUS SCSI controllers:
----------------------------- cut ----------------------------------
I did (and published) some benchmarks of SCSI MSCP-emulating
controllers probably a decade ago. And indeed the CMD CQD 440 was the
winner. But they all beat the pants off a RQDX3!
Here are the peak data rates measured for read and write 64
blocks-at-a-time:
Read Write
---------- ----------
Andromeda SCDC 2.298 MB/s 1.131 MB/s
CMD CQD440 2.397 MB/s 1.525 MB/s
CMD CQD220 1.418 MB/s 0.882 MB/s
CMD CQD220A 2.088 MB/s 1.409 MB/s
DEC RQZX1 1.379 MB/s 1.097 MB/s
Viking QDT 0.846 MB/s 0.704 MB/s
DEC RQDX3 0.164 MB/s 0.161 MB/s
The benchmarks were done under RT11FB 5.7 doing 1, 2, 4, 8, 16,
32, and 64 block-at-a-time READW's and WRITW's to 16384-block
data files. A KDJ11B (PDP-11/73) CPU with 2 Megabytes of Clearpoint
non-PMI memory was used for the bencharmks. With the SCSI
controllers a Barracuda 7200 RPM ST15230N drive was used; with
the RQDX3 a RD52 drive was used.
