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Technical Terms
Evolution of 1/2-inch
Cartridge Tape
| 3480 |
18-track |
No Compression
No
Superblocking
No maximum record size
Must write with
thick tape
Thick tape (575 feet)
Maximum capacity of 200
megabytes (MB) per cartridge |
| 3490 |
18-track |
Added
compression
Added superblocking
Restricted superblocks
to 102,400 bytes
Compression off = 3480
Must write with
thick tape
Maximum of 600 MB per cartridge (with 3:1
compression) |
| 3490E |
36-track |
Always
superblock
Restricted superblocks to 461,824 bytes (this is
violated) Can use thin or thick tape
Thin tape (1100
feet)
Write from BOT to EOT, then EOT back
Compression
can be on or off
Maximum of 2400 MB per cartridge (with 3:1
compression) |
| 3590 |
128-track |
Compression
is standard (LZ1)
New cartridge and tape (same form
factor)
Serpentine recording
Data transfer rate of 9 MB
/ sec (uncompressed)
High-speed search speed of 5
m/sec
Maximum of 30 GB per cartridge (with 3:1
compression) |
36-track Versus
18-track
Wrapping Back to BOT for 36-Track
18-track writes
tracks 1-18 to EOT
36 track writes tracks 1-18 to EOT, then writes tracks 19-36 back
to BOT
GAS GAUGE on 18 and 36 reflect distance to end of recording
Tape
Capacity
How to get 24 Gigabytes with a CSL
| 18-track, Thick, no comp
|
200 MB |
|
| 36-track, Thick Tape, no compression
|
400 MB |
|
| 36-track, Thin Tape, no compression
|
800 MB |
|
| 36-track Thin Tape with compression
|
2400 MB |
( 2.4 GB) |
| 10 tapes, 36-track Thin Tape with
compression |
24,000 MB |
(24 GB)
|
Superblocking
Put multiple user records in a single tape record; Up to 2048
packets (user records) in a “physical tape record;” Eliminate
interblock gaps, IBGsIBG = 2 mm or .079 inches; If you have 50,000
fewer IBGs on tape, then you have 50K * 3K = 150 megabytes more;
Small records do not take a small amount plus an IBG; They take only
a small amount of tape length.
Tape Speed and Data
Transfer Rates
Tape Speed
Data Rate to Tape
SCSI Data Rate
| SCSI |
5 Megabyte/sec |
| Fast SCSI |
10 Megabyte/sec |
| Wide SCSI |
10 Megabyte/sec |
| Fast and Wide SCSI |
20
Megabyte/sec |
SCSI
Connections
| DIFFERENTIAL |
SINGLE-ENDED |
| Wide 68 pin |
Wide 68 pin |
| Centronics 50 pin |
Centronics 50 pin |
| High density 50 pin |
High density 50
pin |
Notes: Single-ended FAST SCSI is pushing the SCSI specification.
Short cables and Active terminators are recommended
Streaming
Drive
3 factors for streaming; Data rate from SCSI; Larger
records, but small enough to fit 4 in buffer; Lower SCSI/DRIVE
overhead; Recommend records 64KB to 256KB; Data rate must at least
match data rate to tape; Faster SCSI data rate is needed to mask
SCSI/DRIVE overhead; Cannot mask overhead when superblocking with
small records; SCSI/DRIVE overhead is multiplied by number of
packets in a superblock
Compression
COMPRESSION on average: turns 3 MB to 1; If Tape data rate
is 3 Megabytes/sec with compression data rate is 3*3 Megabytes/sec =
9 Megabytes/sec; COMPRESSION TAKES TIME HARDWARE COMPRESSION can put
data into the buffer at 9 Megabytes/sec; SOFTWARE COMPRESSION can
put data into the buffer at 4.5 Megabytes/sec.
18/36Mix
Writes
18-track with 36-track head; Erases in Wrap 2 while writing in wrap
one; If write appending (first write not at BOT)
- Erases Wrap 2 for 100 millimeters
- Writes 15 erase gaps ( 100 millimeters worth)
- Writes data
Always write in mode drive was reading; Write at BOT checks
configured density.
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