I know I am going to start another round of discussion with the enclosed subject, so I thought I would capture the facts first.

I wrote a program that would write 1000 records on the CT 729 II number 1.
I used 80 character records with a blocking factor of 1,2,4,8,16 and 32.
I timed how long it took to write a 1000 records at the various record lengths.
The attached spread sheets shows the results.
Saving tape by blocking is a small savings compared to the effective bandwidth of the tape drive at larger block sizes.

If you have any questions, let me know.

Overview

Sheet 1: Transfer Rates

Magnetic Tape
No. of units that can be connected						6 Units
No. of chars/linear inch of tape						556 Char/inch
Channels or tracks on the tape						7 Tracks/tape
Blank tape separating each record						0.75 Inches
Tape speed						75 Inches/sec
Transfer rate						15,000 to 62,500 Char/sec
Start time						7.3 or 10.8 Millisec
Stop time						7.3 or 10.8 Millisec
Average time for experienced
operator to change reel of tape						60 - 120 Seconds
Physical properties of tape
Width						0.5 Inches
Length of reel						2,400 Feet
Composition						Mylar
Two tape units can be specified:						729 II or 729 IV.

Records	Record Length	Blocking Factor	Total Data	Record Time	Transfer rate
1000	80	1	80,000	12.0	6,667
1000	160	2	160,000	14.5	11,034
1000	320	4	320,000	19.5	16,410
1000	640	8	640,000	26.5	24,151
1000	1280	16	1,280,000	43.0	29,767
1000	2560	32	2,560,000	73.0	35,068

100% transfer rate 75 ips * 556 bpi =					41,700

Records	Record Length	Blocking Factor	Record Length IN	Record Time	Records Time	Per Cent Transfer	Capstaan Time
1000	80	1	0.14	0	1.92	15.99%	10.08	ms
1000	160	2	0.29	0	3.84	26.46%	10.66	ms
1000	320	4	0.58	0.01	7.67	39.35%	11.83	ms
1000	640	8	1.15	0.02	15.35	57.92%	11.15	ms
1000	1280	16	2.3	0.03	30.70	71.38%	12.3	ms
1000	2560	32	4.6	0.06	61.39	84.10%	11.61	ms

							11272.78	ms