Jerry Weiss j...@ieee.org
> On Nov 30, 2015, at 7:12 PM, Johnny Billquist <b...@update.uu.se> wrote: > > On 2015-12-01 02:06, Jerry Weiss wrote: >> >> >> The TU58 was a block addressable using a cassette tape drive famously(?) >> called DECtape II. File placement on the two different linear tracks was a >> necessary art, especially if you were booting RT11 regularly. This helped >> it to stream or not rewind in sensitive places. The 1:2 interleave was >> “built-in” to the block formatting (see >> EK-0TU58-UG-001_TU58_DECtape_II_Users_Guide_Oct78.pdf). > > I wasn't aware that it did any block interleaving. But yes, file placement > was extremely important. Are you sure it interleaved blocks? See page 1-4 "Two tracks, each containing 1024 individually numbered, firmware-interleaved "records." Firmware manipulates 4 records at each operation to form 512-byte blocks" Also figure 1-5. Not only interwoven, but reversed for bi-directional r/w I believe. Jerry
