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IDEDOS

1,454 bytes added, 20:42, 27 March 2011
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[[category:Specifications]]
IDEDOS is a hard disk formatting scheme designed for ZX Spectrum computers and clones. It was designed by Garry Lancaster for his [[+3e]] ROMs, and extended by Jarek Adamski to support his ZXVGS, CPM22QED and YaPaDOS operating systems.
==Format==
''Note: The following is not an official specification, it has been reverse engineered from hard disk images and information collected from various sources. The labels given to bytes are entirely arbitrary and should not be taken as the official labels.'' IDEDOS supports up to 65535 partitions on a hard disk, with a theoretical maximum partition size of 2TB. However IDEDOS does not support [http://en.wikipedia.org/wiki/Logical_Block_Addressing LBA mode] therefore the hard disk capacity is limited to 128GB by the limitations of [http://en.wikipedia.org/wiki/Cylinder-head-sector CHS addressing]. ====8-bit vs 16-bit interfaces for Z80 based computers====Since the [[Z80]] microprocessor has as an 8-bit data bus and IDE requires a 16-bit data bus some circuitry is required to combine a pair of 8-bit read/write operations into a single 16-bit operation. This extra circuitry increases cost and complexity in a hard disk interface so some interfaces omit this circuitry and simply treat the IDE bus as a normal 8-bit wide I/O device. This means that when any 16-bit word is read from or written to the hard disk, the upper byte is simply ignored, therefore half the hard disk's capacity cannot be utilised by computer.IDEDOS supports these halved capacity interfaces as it simply means that each hard disk sector contains 256 bytes instead of the standard 512 bytes. Software which reads from an IDEDOS formatted disk should not therefore make assumptions about the number of bytes per sector as it depends on the hardware used to format the disk.
====The IDEDOS System Partition====

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