> On Jun 11, 2026, at 4:34 PM, Fred Cisin via cctalk <[email protected]>
> wrote:
>
> On Thu, 11 Jun 2026, Tom Gardner via cctalk wrote:
>> Ramac had fifty 2 foot diameter double sided platters, and could hold a
>> total of about 5MB.'
>> The IBM 350 disk storage capacity was 5 million 6-bit characters == 3.75
>> MB.
>
> Thank you, I couldn't remember how many bytes per track to calculate
> accurately. They might not have been multiples of 128? Long, long ago, I was
> told 100 bytes per sector?
https://www.bitsavers.org/pdf/ibm/305_ramac/22-6264-1_305_RAMAC_Manual_of_Operation_Apr57.pdf
has the answer:
50 surfaces, 100 tracks per surface, 10 sectors per track, 100 characters per
sector.
Multiples of 10 show up in later products too, like the 1311 disk packs for the
IBM 1620.
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.
paul
