Sector Interleave

Jerry Weiss jsw at
Mon Nov 30 19:20:26 CST 2015

Jerry Weiss
jsw at

> On Nov 30, 2015, at 7:12 PM, Johnny Billquist <bqt at> 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.


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