The ZX Spectrum +3e is a replacement ROM for the ZX Spectrum +3 which fixes several bugs, improves the BASIC, and introduces support for hard drives and compact flash cards. It was created by Garry Lancaster, and its homepage is .
Extended eXtended Disk Parameter Block
The +3e has an "extended XDPB" based on the +3DOS XDPB. The data is ordered as follows
0x0000 SPT SPT BSH BLM EXM DSM DSM DRM DRM AL0 AL1 CKS CKS OFF OFF PSH 0x0010 PHM fl1 tps spt fsn ssz ssz glr glf fl2 fzf fl3 drl fdu lac lac 0x0020 lac nfo nfd nfd lud lud cka cka aba aba lda lda sra sra swa swa key: SPT: Records Per Track BSH: Block Shift: 128 * 2^BSH BLM: Block Mask: 128 * (BLM + 1) EXM: Extent Mask DSM: Number of blocks - 1 DRM: Number of directory entries - 1 AL0: AL0 directory bitmap AL1: AL1 directory bitmap CKS: Size of checksum vector OFF: Reserved tracks PSH: Physical sector shift PHM: Sector size fl1: Flags relating to sidedness tps: Number of tracks per side spt: Number of sectors per track fst: First physical sector number ssz: Sector size glr: Gap length (read/write) glf: Gap length (format) fl2: Flags relating to multitrack/modulation/skip fzf: Freeze flag fl3: Flags relating to drives drl: Drive letter (ascii) fdu: FD unit number for drive B: lac: Last access (FRAMES) nfo: Number of files open on drive nfd: Number of free director entries lud: Last used directory entry number cka: Address of checksum vector aba: Address of allocation bitmap lda: Address of routine to login a disk sra: Address of routine to read a sector swa: Address of routine to write a sector
When the +3e creates a +3DOS hard disk partition it stores the first 28 bytes of the eXDPB in the type specific data section of the partition table entry. The values for the parameters are set as follows:
SPT: always 0x0200 BSH: dependent upon the size of the partition BLM: dependent upon the size of the partition EXM: dependent upon the size of the partition DRM: always 0x01FF AL0: dependent upon the size of the partition AL1: always 0x00 CKS: always 0x8000 OFF: always 0x0000 PSH: always 0x02 PHM: always 0x03 fl1: always 0x00 tps: dependent upon the size of the partition spt: always 0x80 fst: always 0x00 ssz: always 0x0200 glr: always 0x00 glf: always 0x00 fl2: always 0x00 fzf: always 0x00
The following table shows relationship between disk parameters and partition size:
|Partition size||Block size||BSH||BLM||EXM||AL0|
|1-4 MB||2 kB||0x04||0x0F||0x00||0xFF|
|5-8 MB||4 kB||0x05||0x1F||0x01||0xF0|
|9-16 MB||8 kB||0x06||0x3F||0x03||0xC0|
The number of tracks per size (tps) is equal to the partition size in megabytes multiplied by sixteen, e.g. 0x30 for a 3 megabyte partition. The exception to this is the case of a 16 megabyte partition which sets the tps parameter to 0xFF; the maximum value it can store. This means that the filesystem is actually slightly less than 16 megabytes (64kB less to be precise).