The document discusses magnetic tapes and their use for data storage. It describes how tapes provide sequential but not random access to data. It then compares different tape systems based on media format, loading method, storage capacity, track layout, and data transfer rates. An example of a high-performance tape system is provided. The document also discusses how data is organized and stored on tapes, including track layout, blocking, and estimating tape length and data transmission times.

1. MAGNETIC TAPES
BY
SHREYAS LAKSHMAN SWAMY – 4VV19IS095
PURUSHOTTAM B N – 4VV20IS407
VIVEK V KAMATH – 4VV19IS123

2. Magnetic tapes
Magnetic tape is a device that
provides no direct
(random)accessing facility, but
can provide very rapid sequential
access to data.

3. Types of tape systems
● There has been a tremendous improvement in tape technology in the past years
. There are now a variety of tape formats with prices ranging from $150 to
$150,000 per tape drive.

4. Comparison of some current tape systems
Tape Model Media Format Loading Capacity Tracks Transfer
Rate
9-track one-half inch
reel
Autoload 200 MB 9 linear 1 MB/sec
Digital linear
tape
DLT cartridge Robot 35 GB 36 linear 5 MB/sec
HP Colorado
T3000
One-quarter
inch cartridge
Manual 1.6 GB Helical 0.5 MB/sec
StorageTek
Redwood
One-half inch
cartridge
Robot
silo
50 GB Helical 10 MB/sec

5. ANEXAMPLEOFA HIGH-PERFORMANCETAPESYSTEM
The StorageTek Redwood SD3 is
one of the highest-performance tape
systems available in 1997. It is
usually configured in a silo that
contains storage racks, a tape robot
, and multiple tape drives. The tapes
are 4-by-4-inch cartridges with one-
half inch tape . The tapes are
formatted with helical tracks.

6. Organization of data
● On a tape , the logical position of a byte within a file corresponds directly to its
physical position relative to the start of the file .
● If there are 9 tracks , the nine bits that are at corresponding positions in the nine
respective tracks are taken to constitute 1 byte , plus a parity bit . So this slice is
called a frame.

7. ● The parity bit is not part of the data but is used to check the validity of the data.
● If the odd parity is in effect , this bit is set to make the number of 1 bits in the
frame odd.
● Blocks are separated by interblock gaps , since tapes cannot start or stop
instantaneously.
● Performance differences among drives can usually be measured in terms of 3
quantities :
1. Tape density – commonly 800, 1600 or 6250 bits per inch per track
2. Tape speed – commonly 30 to 200 inches per second and;
3. Size of interblock gap – commonly between 0.3 inch and 0.75 inch

8. Estimating tape length requirements
● Performance of tape drives can be measured in terms of 3 quantities :
 Tape density = 6250 bpi ( bits per inch per track)
 Tape speed = 200 ips ( inches per second )
 Size of interblock gap = 0.3 inch
File characteristics:
 Number of records = 1,000,000
 Size of record = 100 bytes
How much Tape is really needed ?

9. ● It depends on the blocking factor (how many records per data block).
Let us compute the space requirement in two cases:
A) Blocking factor = 1
B) Blocking factor = 50
 Space requirement ( s )
 b = length of data block (in inches)
 g = length of interblock gap (in inches)
 n = number of data blocks
● s = n x (b + g)

10. A) Blocking factor = 1
 b = block size/tape density = 100 bytes/6250 bpi= 0.016 inch
 n = 1,000,000 (recall blocking factor is 1)
 s = 1,000,000 x (0.016 + 0.3) inch = 316,000 inches ∼ 26,333 feet
B) Blocking factor = 50
 b = 50 x 100 bytes/6,250 bpi = 0.8 inch
 n = 1,000,000 records/50 records per block = 20,000 blocks
 s = 20,000 x (0.8 + 0.3) inch = 22,000 inches ≈ 1,833 feet

11. Estimating Data Transmission Times
Nominal Rate = tape density (bpi) x tape speed (ips)
● In a 6,250 - bpi , 200 - ips tape :
 Nominal Rate = 6,250 bytes/inch x 200 inches/second = = 1,250,000
bytes/sec ∼ 1,250 KB/sec

12. Effective Transmission Rate = E.R.D. x tape speed
● In the previous example:
A) E.T.R. = 316.4 bytes/inch x 200 inches/sec = 63,280 bytes/sec
∼ 63.3 KB/sec
B) E.T.R. = 4,545.4 bytes/inch x 200 inches/sec = 909,080
bytes/sec ∼ 909 KB/sec
● Note : There is a tradeoff between increasing blocking factor for
increasing speed & space utilization and decreasing it for reducing the
size of the I/O buffer.

13. THANK YOU

14. TIMELINE
It’s the second planet
to the Sun
2019
It’s the closest planet
to the Sun
2017
It’s a gas giant and the
biggest planet
2020
Despite being red,
Mars is a cold place
2018

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MERCURY MARS JUPITER
2018 647 984 268
2019 752 546 875
2020 455 856 340

17. THIS IS A MAP
It’s the closest
planet to the Sun
60%
It’s the second
planet to the Sun
78%

18. OUR PARTNERS
Venus is the second
planet to the Sun
VENUS
Saturn is the ringed one
and a gas giant
SATURN
It’s the farthest planet
from the Sun
NEPTUNE

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