# XP Pro will not boot if microdrive in cardreader

hssutton 09:51 10 Dec 2003
Locked

Can anyone explain why my PC, XP Pro will not boot if I leave my microdrive in the cardreader, but will boot with a compactflash inserted.
A puzzle more than a problem.

Harry

hssutton 13:36 10 Dec 2003

LeadingMNMs Thanks for the input, however the problem is nothing to do with the boot sequence. more of a problem peculiar to the microdrive.

hssutton 19:41 10 Dec 2003

Have found the problem, there is a "Cyclic Redundancy" half way through the microdrive. Now what on earth is a "Cyclic Redundancy"

Big Elf 19:45 10 Dec 2003

CRC or "cyclic redundancy code") A number derived from, and stored or transmitted with, a block of data in order to detect corruption. By recalculating the CRC and comparing it to the value originally transmitted, the receiver can detect some types of transmission errors.

A CRC is more complicated than a checksum. It is calculated using division either using shifts and exclusive ORs or table lookup (modulo 256 or 65536).

The CRC is "redundant" in that it adds no information. A single corrupted bit in the data will result in a one bit change in the calculated CRC but multiple corrupted bits may cancel each other out.

CRCs treat blocks of input bits as coefficient-sets for polynomials. E.g., binary 10100000 implies the polynomial: 1*x^7 + 0*x^6 + 1*x^5 + 0*x^4 + 0*x^3 + 0*x^2 + 0*x^1 + 0*x^0. This is the "message polynomial". A second polynomial, with constant coefficients, is called the "generator polynomial". This is divided into the message polynomial, giving a quotient and remainder. The coefficients of the remainder form the bits of the final CRC. So, an order-33 generator polynomial is necessary to generate a 32-bit CRC. The exact bit-set used for the generator polynomial will naturally affect the CRC that is computed.

Most CRC implementations seem to operate 8 bits at a time by building a table of 256 entries, representing all 256 possible 8-bit byte combinations, and determining the effect that each byte will have. CRCs are then computed using an input byte to select a 16- or 32-bit value from the table. This value is then used to update the CRC.

Ethernet packets have a 32-bit CRC. Many disk formats include a CRC at some level.

Big Elf 19:47 10 Dec 2003

hssutton 20:28 10 Dec 2003

Wow! I guess that means my microdrive is knackered.
I can still access the first 250Mb then I get the Cyclic Redundacy message. Does anyone know if this gets progressively worse.

Big Elf 20:38 10 Dec 2003

I assume the CRC algorithm is suggesting a potential rather than an actual disc failure.

Is there a disc utility avaialable from IBM/Hitachi that allows you to run a disk check to confirm this?

Depending on the age it may still be covered by the warranty/goodwill.

hssutton 21:08 10 Dec 2003

Thanks or the suggestion Big Elf, I will check out the IBM site

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