Monday, January 31, 2011

Mode ในการเขียน CD

Audio CD:
just plain "audio". There are no Modes...

Data CD:
- ข้อมูลทั่วไปสามารถเขียนใน MODE-1
หรือ CD-ROM/XA Mode 2/Form 1
ซึ่งจะให้พื้นที่ในการเขียนข้อมูลมากกว่า MODE-1 อยู่เกือบ 14%

- ข้อมูลที่สามารถผิดพลาด(บ้าง)ได้ เช่น Video
สามารถเขียนใน MODE ของ CD-ROM/XA Mode 2/Form 2 ได้

Data in a CD-ROM is organized in frames and sectors.
The smallest entity in the CD format is called a frame, and holds 24 bytes.
A CD-ROM sector contains 98 frames, and holds 2352 bytes.

standard 2048-byte physical format for data CDs sectors, with error correction

MODE-1 divides the 2352 byte data area
defined by the Red Book (physical format for audio CDs) standards
12 bytes of synchronization information
, 4 bytes of header data
, 2048 bytes of user data
, and 288 bytes of error correction and detection codes.

These codes help prevent the data from becoming corrupted
, which could lead to errors for executable data.

(ส่วนอื่นๆนอกจาก User data แล้ว
ตัว Writer เป็นผู้คำนวน + จัดการให้
ดังนั้น สิ่งที่ตามมาก็คือ
an "ISO" is created by copying an entire disc, from sector 0 to the end, into a file.
Because the image file contains "cooked" 2048-byte sectors and nothing else
, it isn't possible to store anything but a single data track in this fashion.

Audio tracks, mixed-mode discs, CD+G, multisession, and other fancy formats can't be represented.)

The Mode 1 CD-ROM ECC is independent of
and in addition to the CIRC encoding.
It uses a Reed-Solomon Product Code (RSPC)
to achieve a combined error rate of 1 error per 1e15 (quadrillion) bits.

Mode 2 provides 14% more user data space than Mode 1
by omitting error correction
, since a read error in audio or video
will only cause a small flaw
which may not even be detectable to humans.

(Video CDs are classified as Mode 2 Form 2.)

MODE-2 usually used for CD-ROM/XA ( eXtended Architecture )

(ดังนั้นจึงเรียกรวมว่า CD-ROM/XA MODE-2)

CD-ROM/XA MODE-2 defines two forms:
FORM-1 2048 bytes of data, with error correction
FORM-2 2324 bytes of data, no ecc

CD-ROM/XA Mode 2/Form 1
acceptable for data storage

CD-ROM/XA Mode 2/Form 2
should only be used for audio or video, never for data.

ใช้ Mode ไหนดี
Nero normally writes ISO data in the CD sector format Mode 1.
However Nero also supports the so-called XA-Format for ISO data.
The best solution is to use Mode 1 unless a multimedia application demands CD-ROM/XA.

Note that mixing MODE-1 (CD-ROM) and MODE-2 (CD-ROM/XA) sessions
on a single disc isn't allowed.
You could create such a thing,
but many CD-ROM drives will have a hard time recognizing it.

เรียบเรียงโดย สิริพงษ์ พงศ์ภิญโญภาพ


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