4 ms·

> Unlike most block devices these are devices that do not enjoy seeking of any kind. Old-school DECtapes were actually random-access, seekable block devices!

> Unlike most block devices these are devices that do not enjoy seeking of any kind. Old-school DECtapes were actually random-access, seekable block devices! They help 578 blocks of data, each block being 512 bytes (or to be more period correct, 256 16 bit words), so 144kiB. They could be read/written in both directions. When mounted on a tape drive, the OS (like DEC RT-11) would treat it just like how a PC DOS computer treats a floppy: you could get a directly listing, work with files, etc. The random access nature caused the tape to move quickly back and forth across the tape head, a process known as "shoe shining". https://youtu.be/ZGBS8mBAfYo?t=579 https://youtu.be/ZGBS8mBAfYo?t=579

StillBored 5y ago
Tape can do random seeks, but its generally append only. LTO, though supports partitioning which is utilized by LTFS (https://www.lto.org/linear-tape-file-system/ https://www.lto.org/linear-tape-file-system/) to provide a mountable filesystem abstraction. It works just like any other filesystem, but one has to remember that seeks are much slower than HDs and that overwriting/updating a file basically is like a versioned FS where the old data is still being stored. Edit: Also, tape formats tend to come in two scan methods since they are generally wider than the tape heads (which frequently are actually multiple heads). Helical scan (think VHS/DAT) and serpentine. LTO is serpentine which means it writes a track from beginning to end, then writes the next track in "reverse" from end to beginning, then the next track again from beginning to end. Back and forth until it hits its track limit. So basically just about every modern drive reads and writes in both forward and reverse. Although shoe shining (backing up to start the next read/write) is still a thing despite variable speed drives which try to speed match to the data rate the host is reading/writing at.
tssva 5y ago
The Coleco Adam home computer also had tape drives which were random-access seekable block devices. 2 tracks with 128 1k blocks per track for a total capacity of 256k. Coleco called their tapes digital data packs. They were standard compact cassette tapes with some additional holes. If you drilled the appropriate holes you could use standard tapes instead of paying the Coleco premium. CP/M required booting from a block device and as far as I know the Coleco Adam was the only computer which could boot CP/M from a tape. Once booted to CP/M the tape drives were treated just as floppies.
rbanffy 5y ago
I've seen AIX being installed from a DDS tape, after booting from said tape. Fun times.
EvanAnderson 5y ago
This makes me think about the Stringy Floppy: https://en.wikipedia.org/wiki/Exatron_Stringy_Floppy https://en.wikipedia.org/wiki/Exatron_Stringy_Floppy

StillBored 5y ago

Tape can do random seeks, but its generally append only. LTO, though supports partitioning which is utilized by LTFS (https://www.lto.org/linear-tape-file-system/ https://www.lto.org/linear-tape-file-system/) to provide a mountable filesystem abstraction. It works just like any other filesystem, but one has to remember that seeks are much slower than HDs and that overwriting/updating a file basically is like a versioned FS where the old data is still being stored. Edit: Also, tape formats tend to come in two scan methods since they are generally wider than the tape heads (which frequently are actually multiple heads). Helical scan (think VHS/DAT) and serpentine. LTO is serpentine which means it writes a track from beginning to end, then writes the next track in "reverse" from end to beginning, then the next track again from beginning to end. Back and forth until it hits its track limit. So basically just about every modern drive reads and writes in both forward and reverse. Although shoe shining (backing up to start the next read/write) is still a thing despite variable speed drives which try to speed match to the data rate the host is reading/writing at.

tssva 5y ago

The Coleco Adam home computer also had tape drives which were random-access seekable block devices. 2 tracks with 128 1k blocks per track for a total capacity of 256k. Coleco called their tapes digital data packs. They were standard compact cassette tapes with some additional holes. If you drilled the appropriate holes you could use standard tapes instead of paying the Coleco premium. CP/M required booting from a block device and as far as I know the Coleco Adam was the only computer which could boot CP/M from a tape. Once booted to CP/M the tape drives were treated just as floppies.

rbanffy 5y ago

I've seen AIX being installed from a DDS tape, after booting from said tape. Fun times.

EvanAnderson 5y ago

This makes me think about the Stringy Floppy: https://en.wikipedia.org/wiki/Exatron_Stringy_Floppy https://en.wikipedia.org/wiki/Exatron_Stringy_Floppy