Drive type in 3b1

[Boyd Ostroff]

In article <2130 at public.BTR.COM> thad at public.BTR.COM (Thaddeus P. Floryan) writes:
>In article <107 at kbvan.com> dave at kbvan.com (Dave Van Allen) writes:
>>The front plate on the system says it has a 67Meg drive, but there
>>is no 67 meg drive in the type table. The nearest maych is 64meg but
>
>The 64MB drive selection is the correct one due to how spare sectors are
>allocated on the drive.

Perhaps this is nit-picking, but I think you're wrong.  The 3B1 actually
does only have a 64MB drive.  The discrepancy comes from the definition
of a "megabyte".  Recall that one kilobyte (K) is actually 1024 bytes, not
1000.  A megabyte is 1024 K = 1,048,576 bytes, NOT 1,000,000 bytes.  Therefore,
64 megabytes actually equals 67,108,864 bytes - this is where the 67MB figure
comes from.  Disk and computer companies like the use the most "optimistic"
way of computing the hard drive capacities :-)

The spare sector concept is correct, but the numbers are wrong.  Due to the
fact that the 3B1's disk controller can only handle a certain number of
sectors (I forget the details), there are "spares" on each track which are
used for mapping bad blocks.  The full, formatted capacity of the Miniscribe
drive is actually 71MB, but the unix-pc can only utilize 67MB.

Of course, you're going to lose another 4 or 5 MB of your disk space to a 
swap partition, so you'll probably only have 62 MB free once the drive is
formatted.

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