Ade Vickers wrote:

...
> I must admit, I was assuming Sinclair had used 1024 byte blocks on his
> microdrives - I may need to be corrected on that.

Sinclair used 512 byte blocks/sectors on the mdvs. ^_^

(AFAIK) When a cartridge was formatted, the blocks were written with 
decreasing block numbers; thus the highest block still valid gave the max 
capacity of that format - duff sectors and the [root] directory would 
decrease the available blocks.

The space available in K is simply half the number of free sectors.

For floppies, it depends upon the capacity of the disk as to how many 
sectors = 1 block.  eg for ED, it was 3 sectors/block.

>>Of course, the capacity decreases when you format the disc as 
>>well (how did they work out the unformatted capacity, 
>>because, if it is unformatted then you cannot store anything on it !)
> 
> Stephen Usher's description of the perils of formatting is amongst the best
> I've ever seen. It's true that you can lose staggering amounts of disk space
> to a bad file format... 

My ED disks are described as 4M unformatted.  Under DOS (fat) they provide 
2.88M, on the QL, I get 3.2M.


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