28 Apr
2005
28 Apr
'05
8:34 p.m.
Paul Koning wrote:
Jerome> Has anyone any explicit knowledge and / or
experience of a
Jerome> TK70 tape drive on a PDP-11?
I don't know if it was ever sold, but there's code in RSTS V10.1 to
recognize a TKQ70. That makes sense; the OS doesn't much care so long
as the controller speaks (T)MSCP and isn't too fast to overrun the
bus.
Jerome Fine replies:
I wonder if that was done to help avoid the problems
with the TK50 drive? At one point, I heard that the
TQK70 was developed to be used with the TK50 in order
to correct some of the problems that the TK50 drive
exhibits with the TQK50 controller. During my use
of the TK70 drive, I sometimes placed the TK50 on
the TQK70 controller and noticed a bit of an improvement
with the TK50 drive. I never investigated all of the
possible modes of operation, so I can't suggest any
specific improvements.
As for being faster, the TQK70 / TK70 almost certainly
has the ability to buffer records internally and do
a read of the next record. I conclude that to be true
since I note the following:
(a) I often make a backup image of an RT-11 partition
which requires a file of 32 MBytes. This takes about
7 minutes on a TK70.
(b) I then do a verify of the file against the original
RT-11 partition. Using a TK50, it was almost impossible
to complete due to the TK50 drive having to rewind all
the time when the program (BUP.SAV under RT-11) stopped
to read the disk drive and then compare the two sources
of data (tape buffer with hard disk buffer). BUT with the
TK70, the verify time was also 7 minutes - leading me to
assume that while the BUP.SAV program was comparing the
data in the two RAM buffers, the TQK70 continued to transfer
the bytes from the next tape record (always 8192 bytes)
into a hardware buffer within the TQK70 controller. As
soon as the BUP.SAV program finished the verify of the
current RAM buffers, a read request to the TQK70 that
took place sufficiently soon before the end of the tape
record on the TK70 media was reached was able to keep the
TK70 tape drive in streaming mode and no rewinds were ever
(or extremely rarely) required. I fail to understand how
else the verify time was also 7 minutes. If anyone else
has an alternate explanation, it would be appreciated!
Sincerely yours,
Jerome Fine
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