11 Jun
2026
11 Jun
'26
4:29 p.m.
On Thu, 11 Jun 2026, Paul Koning wrote:
https://www.bitsavers.org/pdf/ibm/305_ramac/22-6264-1_305_RAMAC_Manual_of_O…
has the answer:
50 surfaces, 100 tracks per surface, 10 sectors per track, 100 characters per sector.
Thank you
Multiples of 10 show up in later products too, like
the 1311 disk packs for the IBM 1620.
Some people took a while to get used to
binary.
Then of course there's weird stuff like the
IBM/360 disks with their variable length sectors. Or the CDC mainframes with 322 12-bit
words per sector. Or Electrologica where you could choose one of five sector sizes on a
per-track basis. Or the DEC RS64 with 64 byte sectors, or the word-addressable RF11.
. . . and, if you mix multiple sector sizes on the same track ("Ensoniq
Mirage"?), then you can squeeze even more in.
Reading and even writing differing size "normal WD/IBM format" sectors on
the same tsack, even on the NEC765, but formatting a track with
inconsistent sector sizes requires some weird tricks. shouldn't be
excessively hard on the WD179x controllers, but the NEC765 tries to keep
you away from weird stuff.