From Newsgroup: alt.folklore.computers

According to Rich Alderson <news@alderson.users.panix.com>:

John Levine <johnl@taugh.com> writes:

At Yale our PDP-11 originally had an RK05 single platter 1MB drive in
1974, then we upgraded to a pair of RP02 washing machine sized drives,
20MB each.

We also had a PDP-10 which also used the same RP02 disks. I think I
once experimented with trying to write a PDP-11 formatted disk on the
-10, reading the file system from tape. It was rather exciting since
the 36 bit PDP-10 mapped its words into the disk's 8 bit bytes in
non-obvious ways.

Its perfectly obvious, since the PDP-10 operating systems write 128 word blocks
at all times (even TOPS-20, which simply reads/writes 4 such blocks for each >512 word page in the data stream).

1 sector = 128 words * 36 bits = 64 * 72 bits = 576 * 8 bits

It can't have been that obvious since the 11's disk controller had a PDP-15 mode
bit that read or wrote 18 bit words. The manual doesn't say how they were mapped
into the 11's 16 bit words. The normal PDP-11 mode was 512*8 bits and I think it ignored the rest of the sector.
--
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly
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