Quantum Audio STT2401A 사용자 설명서

Seagate Travan 40 Product Manual 

Page 115 

 

The tracks and bands are arranged to allow approximately constant distance 
between all sequential tracks. Band 1 is located nearest the bottom edge of tape. 
Band 2 is located above band 1. Continuing up sequentially is band 3 and band 4 
(nearest the top edge of tape). The directory track is located between bands 2 and 3. 

All even numbered tracks, and the Directory Track, are recorded in the forward 
direction (the direction from the BOT marker to the EOT marker). All odd numbered 
tracks are recorded in the reverse direction (the direction from the EOT marker to 
the BOT marker). All even numbered tracks are located below the Directory Track; 
all odd numbered tracks are above it. 

Tracks are recorded sequentially beginning with track 0, then track 1, and so on. 
Before recording, data are grouped into blocks, and blocks are grouped into frames 
with 510 blocks per frame.  

Two numbering methods are used for blocks: physical numbering and logical 
numbering. Both numbers start from 0 at the beginning of each partition. 

• 

Physical numbering is related directly to the recorded block on the tape. Each 
new block is given a unique physical number, regardless of its contents. 

• 

Logical numbering does not relate to the blocks physically recorded on the tape; 
rather, this type of numbering is the block numbering system used by the host 
computer. Often the host system operates with logical blocks that are a different 
size from the 512-byte blocks that are physically recorded on the tape. 
 
The host blocks can be larger or smaller than 512-bytes and can also be fixed or 
variable. Fixed host blocks contain the same number of data bytes in each block. 
Variable host blocks may contain a different number of data bytes in each block. 

The format provides both a physical block number for each block recorded on the 
tape and a logical block number that can span more than one physical block. These 
two numbers are recorded in the control field of every block. 

Every track on the tape is recorded in blocks that contain 512 data bytes. The data 
bytes are 8-bit bytes, which are numbered b0 to b7 with b7 being the most significant 
bit. 

A frame is made up of 510 blocks—470 data blocks plus 40 error-correction code 
(ECC) blocks. Figure 16 illustrates the general track layout of sequentially recorded 
frames.