User:Tom94022/350Facts

This is about the 350 - not at all about the systems to which it attached.

The 350 held 3.75 million usable bytes, written and read as 50,000 blocks of 100 characters; each block comprising 100 6-bit characters, each with a parity bit and a space bit and including gaps before (also containing bits) and after each block of data. The core of the proof - it's not an argument any longer - is as follows:

1. The 350 was a hard disk drive offered for purchase by IBM.
2. IBM stated the 350 as having a formatted capacity of 5 million characters.
3. The 350 at its interface exposes a bit serial interface
4. The 5 million character capacity is derived from a specific format applied by IBM to the 350s bit serial interface.
5. IBM stated the character recorded in the 350 as having 8 bits consisting of 6 data bits, 1 parity bit and 1 space bit.
6. Recorded bits for a character are defined as S, 1, 2, 4, 8, 0, X, and R.
7. At the 350 interface, IBM constrains bit R to give each character stored an odd number of "1" bits. It "carries no numeric or logical value."
8. At the 350 interface, IBM constrains bit S to be always written. It "is not used in the bit coding."
9. At the 350 interface, IBM places no limitations on the six other bits per character, so there are six unconstrained bits per character.
10. It is speculation to suggest that either the R bit or the S bit could be used for anything other than what IBM stated.
11. Claims of 7 bits per character in the 350 are widespread; however, this does not match the recorded character code stated by IBM for the 350 which is 8 recorded bits per character.
12. Any source stating or dependent upon "7 bits per character" such as 4.4 MB is using a partial concatenation of the 350 recorded character. Without explanation by these sources, such usage is a meaningless computation.
13. Hard disk drives today are specified at an HDD interface by their vendors in 8-bit bytes having no constraints on the 8 bits (all 256 states available at the HDD interface). Accordingly restating IBMs specified capacity into modern HDD capacity but be done in terms of unconstrained bits at the 350 interface in order to avoid inapposite comparison.
14. Five million characters x 6 unconstrained bits each = 30 million unconstrained bits available at the 350 interface.
15. Thirty million unconstrained bits at 8 unconstrained bits per byte is 3.75 MB as HDDs are specified by today's vendors.
16. Five million characters x 8 constrained bits = 5 MB of something but it is not 5 MB as vendors currently specify HDDs. It is, for example, the number of MB required in a modern HDD required to store the image of all 350 recorded characters; however, in the absence of source explaining this derivation it shouldn't be used in Wikipedia. It is not, for example, the unformatted capacity as such bit serial drives came to be in part specified beginning sometime in the 1970s, the 350 unformatted capacity can be calculated but to do so would approach original research.
17. The most appropriate usable value for comparing the capacity of the 350 to a modern HDD is 3.75 MB. We might as editors reach a consensus that 5.0 MB is permitted but it should be footnoted since it includes constrained bits.

This conclusion is inescapable from this sequence, and I see nothing in any of your comments to refute any of the steps. If you still disagree with this conclusion, please indicate with which numbered point(s) immediately above you disagree; and why; and provide reliable references for your position. Please note: Anything about the 650 or the 355 or BQCD is irrelevant; responses regarding any of those will be interpreted as non-responsive.