Dave, Thanks, I wasn't aware of this subtlety. But this is for the 7970E only, right? Can you boot a 21MX from a 7970B tape with the standard boot ROM? Is your better boot ROM code available? Marc
-----Original Message----- From: cctech [mailto:cctech-boun...@classiccmp.org] On Behalf Of J. David Bryan via cctech Sent: Friday, October 06, 2017 11:11 AM To: Classic Computing List Subject: RE: (Classic Computers) HP 7970 1/2" 9-Track Reel-to-Reel Tape Drive On Tuesday, October 3, 2017 at 20:58, Jay West via cctalk wrote: > Wasn't there some deal where a M/E/F could drive it at 45ips but a > 2100 couldn't (next lower speed)?? You might be thinking of the limitation regarding the use of the 12992D Magnetic Tape Loader ROM with a 1000 M-Series and a 7970E (1600 bpi) operating at 45 ips. This bootstrap loader used skip-on-flag (word-at-a-time) mode, and the data transfer loop could not keep up at tape speeds greater than 37.5 ips. The faster E- and F-Series CPUs could run the bootstrap with the drive configured for the full 45 ips. The 2100 and the 1000 M/E/F-Series machines had no such limitation if DMA/DCPC was used to access the tape drive. DMA wasn't used in the boot loader ROM because the code wouldn't fit in the 64-word ROM size. (That said, I've rewritten the 12992D bootstrap to tighten the timing loops, and it works fine on my 1000 M-Series and 7970E drive. I think the original limitation was due to suboptimal coding.) -- Dave
