Author Topic: symbiface  (Read 5737 times)

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Offline gerald

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Re: symbiface
« Reply #50 on: 09:21, 23 January 13 »
The 128GB limit is mainly due to the 28bit LBA adressing, not the FAT. 128GB=2^28*512Bytes.
To use a bigger drive, you need to support 48bit adressing (EXT command) at drive level.

FAT32 also uses 28bit for addressing clusters within partition, so a partition with 512byte clusters is limited to 128GB.
But by using 32KB cluster,  you can have up to 8TB FAT32 partition.

Obviously, 32K cluster is a big waste on a 8bit system.

Dealing with 48bit LBA is a bit overhelming for a Z80, not that it cannot deal with, but who need more than 128GB partition ?


Offline TFM

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Re: symbiface
« Reply #51 on: 21:26, 23 January 13 »
Well, I have 48 bit LBA running for FutureOS as far as low level routines go. But I had to stop developpment of that in 2008 when I moved to NOLA. What I want to say is that 48 bit LBA is not a problem at all.
 
Sure, 32 KB blocks are a big waste, but any kind of hard disc is a big waste per se anyway  :laugh:
 
If I got you right we still can have some 128 GB partitions on the same hard disc using FAT32, I'm a bit out of that memories now... :o
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Offline gerald

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Re: symbiface
« Reply #52 on: 22:06, 23 January 13 »
Well, I have 48 bit LBA running for FutureOS as far as low level routines go. But I had to stop developpment of that in 2008 when I moved to NOLA. What I want to say is that 48 bit LBA is not a problem at all.
Well, Compact flash are not (yet) that big, so I did not implement 48bit LBA support in my FAT32 and CF access routines  ;D

If I got you right we still can have some 128 GB partitions on the same hard disc using FAT32, I'm a bit out of that memories now... :o
Yes, as long as the MBR can handle the disk (2.2TB limit), or use GPT for bigger drive.  ::)

Offline TFM

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Re: symbiface
« Reply #53 on: 22:55, 23 January 13 »
Well, I guess, I stick with FAT32 since most computers can read it :)
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Offline rpalmer

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Re: symbiface
« Reply #54 on: 20:45, 24 January 13 »
There is a way to get more space used while still limiting the code to 2^32 sectors (i.e 2.2 TB with 512 bytes sectors) and that is to fix the 48-bit LBA to have the upper 16-bits set to zero all the time. Therefore the code changes might only be minor to handle the IDE command set to cater for the access of drives having capacities above 2.2TB or indeed 128 GB with 512 byte sectors. But for sectors which are larger (like 4096 byte sectors) the buffers in the CPC may be too large to deal with since there is already a limited space for them to allow much of the S/W to work unhinded by a reduced work space. Certainly AMSDOS can not handle it as it has a buffer space of only 512 bytes and sector data indexing limited to 512 bytes.

Also like to point out the a "cluster" is a group of sectors so no matter what the cluster size the media is always limited to the number of sectors.

When i said that FAT32 was limited to 128GB was due to the driver support associated with the normal IDE command set (i.e limited to 2^28 sectors).  Sorry if I misled anyone  ::)
 
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Offline TFM

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Re: symbiface
« Reply #55 on: 23:24, 24 January 13 »
Well, no offense, but if we talk about a CPC with added hard-disc, then we can assume at least a 128 KB system, so there is space for buffers. I'm using one 16 KB block for buffers, guess BonnyDOS does use 16 KB too.
 
Now, the SF2 users all have 512 KB expansion RAM and other IDE solutions may also be used by people already having a memory expansion.
 
IMHO a hard-disc is much more powerful if the system has enough RAM. Guess nobody uses (today) a hard-disc with only 64 KB RAM (I may be wrong though).
 
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