Format - Page 2
- Techical information
From the perspective of the CD-RW System Description, the entire
capacity of a MRW disc consists of a single session containing a single track
of 32 sector fixed packets.
Structure of a CD-MRW Disc
The MRW disc does have this format, but the CD-MRW Defect Management &
Physical Formatting requires additional features, built upon the basic format:
Lead-in, Part A: TOC, no change
Lead-in, Part B: TOC (in sub-channel Q) along with MTA (information
is stored in main channel). Prior to CD-MRW, the lead-in has always been recorded
track-at-once. With this new format, it is recorded as fixed packets. The MTA
use begins with the packet that precedes the pre-gap. When needed, the MTA grows
backward toward the disc center.
Program Area, Part A: Track 1 pre-gap has a fixed size of 150 sectors.
The TDB identifies the track as a fixed packet track with packet size = 32.
Program Area, Part B: The General Application Area (GAA) is a segment
of the track that is NOT covered by the defect management system. This is fixed
at 32 packets (2 MB of user space).
Program Area, Parts Cx: The Defect Managed Area (DMA) consists of
DMA segments, Cx. Each Cx consists of a spares area (SA) followed by a data
area (DA). Each SA must contain 8 packets. Each DA within C1, C2, , Cn-1,
must contain 136 packets for primary data. Cn may contain less than 136 packets,
based upon disc capacity. The DMA is the logical concatenation of all DAs.
Program Area, Part D STA: 33 packets reserved for secondary copies
of the MTA structures.
Lead-out, Part A: Lead-out, no change
The number of Cx is determined as follows: P = number of 32 sector fixed
packets available in the formatted track 1. The number of packets in all Cx
is Pt = P . GAA size . STA size = P . 65. When Pt is divided by 144 (=8 + 136),
there is a quotient Q and remainder R. If R .8, then Q = n, the DA size for
each Cx is 136, and the lead-out begins R packets sooner. If R > 8, then
Q = n . 1, the DA for C1, C2,...Cn-1 is 136, the DA for Cn is R . 8 packets
in length, and the lead-out is not offset into the program area.
The Host's primary address space is the DMA. By default, an LBA is presumed
to refer to this address space. Note that LBAs for the DMA do NOT match LBAs
for a similarly formatted pre-MRW disc. The GAA is available for compatibility
with older systems. The GAA LBA space is 0, 1, 2, 3, , 1023d. Note that
LBAs for the GAA exactly match LBAs for a similarly formatted pre-MRW disc.
When method 2 addressing is used, the LBA of the first sector of the DMA
is at the pre-MRW LBA of (32 + 8)*32 = 1280d. The following table shows the
inequities with pre-MRW LBA references:
The GAA addressing is identical to traditional addressing. The new method
of addressing sectors in the DMA is named "method 3 addressing" in
the CD-MRW Defect Management & Physical Formatting. There is a small problem:
there are two LBA spaces where formerly there was only one. The MRW Mode Page
is used a the method of specific address space selection. The host may toggle
between address spaces (DMA and GAA) by changing the logical units reference
in the MRW Mode Page.
Host Requests/Logical unit Responses
The host may view the MRW disc as a removable magnetic medium with a 2048
byte sector size. This means that the random read capability of MMC is to be
maintained and expanded to include the MRW disc. Additionally, random write
capability must be added specifically for the MRW disc. Within the logical unit,
only the writing of 32 sector fixed packets is allowed. MMC-1 and MMC-2 logical
units share this restriction with their hosts. When MRW disc is present, the
MRW compliant logical unit must not share this restriction with its host. This
is a simple matter of implementing a read/modify/write for packets.
Most of the process for formatting a CD-RW disc into the MRW format is performed
in background. During this background formatting process, the disc is available
for both read and write access within the LBA Space as it shall exist after
formatting has completed. The MRW capable drive shall perform the necessary
tasks to assure this access.
It is possible that the user may wish to remove the disc prior to format
completion. This is allowed, however, the medium must be written in order to
assure read compatibility with Multi-read capable read-only devices. This means
that the disc must be closed. The format will begin again when a host arranges
for the format to be restarted.
- How much free space i can have?
A CD-RW disc is mounted into a MRW capable CD-RW drive. The lead-in ATIP
on this disc indicates that the first lead-in begins at 97:38:20 and the last
possible lead-out begins at 75:04:12. Let us assume that the disc is completely
formatted as a CD MRW disc.
The MRW format requires that the program area be formatted as a single track
of fixed packets with 32 user sectors each. This gives us a maximum of 337812
sectors within the program area (from 00:00:00 to but not including 75:04:12).
At 00:02:00 we will find the first user sector. This means that the first packet
invades the track 1 pre-gap by 5 sectors. So, 337667 sectors may be dedicated
to fixed packets. This yields 8658 packets with 5 sectors remaining (337 812
- (150 - 175) = 39 * 8 658 + 5). The 5 extra sectors are moved into the lead-out.
The GAA requires 32 packets from the beginning of the program area while
the STA requires 33 packets at the end of the program area. This leaves 8 658
- 65 = 8593 packets for the DMA. Each SA/DA pair is 144 packets in length. 8593
= 59*144 + 97, so we may have 59 SA/DA pairs with 97 packets remaining. Of these
97 packets, 8 are reserved for the final SA, leaving 89 packets for the final
DA. The actual number of user sectors in the DMA is 32*(59*136+89) = 25916.