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The Effect of "Tape Blocking"

Note: This information is useful in making a more time and media efficient application using magnetic tapes,
- not of general interest to restoration ;-))

Background:
There is a 3/4 inch gap ("Inter-Record Gap") between Physical Tape Records on tapes of 200, 556 and 800 characters/inch tape format where no data is written. (The above describes the Model 729 tape drives on the restored the 1401s.)
- No user data is placed in this gap. (There is a check character which is written after the last data character - two character positions of no magnetic transitions then the check character is written.)

It is usually considered a good thing to put as many data records into one physical
tape record as practical. This permits more data per tape, and allows more data records to be written or read per second. Factors of physical memory available, statistics of tape defects per length of tape, and other factors, tend to limit the desirable size of physical
tape records.

Because computers are so fast relative to physical I/O, the computer time to block and unblock physical records (as in sorting) is considered rather inconsequential.

The Effect of "Tape Blocking" - from Stan Paddock, Dec. 4, 2001, was in .xls format

Density	Characters per tape record	Tape length per tape record	Records per 2400 foot tape	Total data per 2400 foot tape	Cards per 2400 foot tape	Number of 2000 card boxes	Weight of Cards	Cards per minute	Factor over IBM 1402 card reader
200	80	1.15	25043.48	2,003,478	25,043	13	175	2,544	3
200	160	1.55	18580.65	2,972,903	37,161	19	260	3,774	5
200	240	1.95	14769.23	3,544,615	44,308	22	310	4,500	6
200	320	2.35	12255.32	3,921,702	49,021	25	343	4,979	6
200	400	2.75	10472.73	4,189,091	52,364	26	367	5,318	7
200	480	3.15	9142.86	4,388,571	54,857	27	384	5,572	7
200	560	3.55	8112.68	4,543,099	56,789	28	398	5,768	7
200	640	3.95	7291.14	4,666,329	58,329	29	408	5,924	7
200	720	4.35	6620.69	4,766,897	59,586	30	417	6,052	8
200	800	4.75	6063.16	4,850,526	60,632	30	424	6,158	8
Density	Characters per tape record	Tape length per tape record	Records per 2400 foot tape	Total data per 2400 foot record	Cards per 2400 foot tape	Number of 2000 card boxes	Weight of Cards	Cards per minute	Factor over IBM 1402 card reader
556	80	0.89	32218.91	2,577,513	32,219	16	226	3,272	4
556	160	1.04	27751.82	4,440,291	55,504	28	389	5,637	7
556	240	1.18	24372.60	5,849,425	73,118	37	512	7,426	9
556	320	1.33	21727.00	6,952,640	86,908	43	608	8,827	11
556	400	1.47	19599.51	7,839,804	97,998	49	686	9,953	12
556	480	1.61	17851.51	8,568,722	107,109	54	750	10,878	14
556	560	1.78	16389.76	9,178,268	114,728	57	803	11,652	15
556	640	1.90	15149.29	9,695,546	121,194	61	848	12,309	15
556	720	2.04	14083.38	10,140,032	126,750	63	887	12,873	16
556	800	2.19	13157.60	10,526,081	131,576	66	921	13,363	17
Density	Characters per tape record	Tape length per tape record	Records per 2400 foot tape	Total data per 2400 foot record	Cards per 2400 foot tape	Number of 2000 card boxes	Weight of Cards	Cards per minute	Factor over IBM 1402 card reader
800	80	0.85	33882.35	2,710,588	33,882	17	237	3,441	4
800	160	0.95	30315.79	4,850,526	60,632	30	424	6,158	8
800	240	1.05	27428.57	6,582,857	82,286	41	576	8,357	10
800	320	1.15	25043.48	8,013,913	100,174	50	701	10,174	13
800	400	1.25	23040.00	9,216,000	115,200	58	806	11,700	15
800	480	1.35	21333.33	10,240,000	128,000	64	896	13,000	16
800	560	1.45	19862.07	11,122,759	139,034	70	973	14,121	18
800	640	1.55	18580.65	11,891,613	148,645	74	1,041	15,097	19
800	720	1.65	17454.55	12,567,273	157,091	79	1,100	15,955	20
800	800	1.75	16457.14	13,165,714	164,571	82	1,152	16,715	21
112.50	in/sec
9.38	ft/sec
256.00	seconds
9.85	Min