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Inter-Office Meulorandum

To LRG, Doug Fairbairn Dat~ January 24, 1979

Frem Larry Tesler Location Palo Alto

Subject Notetaker Disk Capacity Organization PARC/SSL

XEROX
Filed on: disk-capacity.memo

The capacity of the Notetaker floppy disk has been advertised as 340,000 bytes. That quantity
assumed double-density, dual sided-disks, and a particular format. rn1is memo summarizes some
possibilities for formatting single-sided disks.

Standard IBM -style fonnats have an overhead in address marks and synch marks equivalent to 60
or more bytes per track plus 50 or more bytes per sector. rIlle WD 1791 can handle non-standard
formats, but below certain unknown minimum values for the synch mark overhead, reliability will
be sacrificed.

Nominal disk capacity (according to Shugart literature):

Single density: 110K
Double density: 220K

File Format (128 byte sectors, IBM style):

Single density: 35 tracks * 16 sectors * 128 bytes = 71,680
[35*(60+-16*(60+ 128