Fads constitute a highly significant but seldom discussed phenomenon in the computer field. Just as fashion styles strike the clothing industry, technological styles strike the computer industry. Time and again, an "idea whose time has come" promises (according to the innovator) to revolutionize the data entry segment, the data computa-tion segment, the data output segment, data com-munications, me inquiry, or some other aspect of EDP.
It is unwise, however, to scoff at either the new ideas or the resurrections of old ideas. Developments in logic organization and production have made many formerly
"impractical" ideas not only feasible but thoroughly practical. This explains why fads are seldom discussed under that name. It is usually difficult to distinguish between a truly innovative development and an im-practical dream. Often the distinction between wishful thinking and practical reality is being eliminated on the design tables just when you're having your biggest laugh.
One such fad-or innovative development-began in the early 1960's with IBM's introduction of disk pack storage units. The unlimited-storage concept enjoyed by magnetic tape could now be shared by disk storage. It could be shown then, as it can be shown now, that for most fIle update processing, magnetic tape provided a more cost-effective medium.
There are several reasons why disk pack drives have attained a dominant position over magnetic tape drives in the face of that performance disadvantage. The important ones are:
• File updating plays a less dominant role in data processing now .
• Disk packs provide a recording medium that is more convenient to maintain in good condition.
Applications which use the information base represented by a data fIle for other than detail and summary reporting of transactions as fIles are updated are not easily implemented with magnetic tape. Single-item inquiry or selective report generation often cannot wait for the next update run. In addition, extensive system software sup-port requires something besides the sequential access mode in which magnetic tape can function efficiently.
Right now, that random access is provided by disk units, and usually by removable-pack disk drives.
The second factor. heavily involves human nature. For tape operations to function effectively, constant vigilance is required to keep the magnetic tape itself in good condition. Installations that have large tape libraries measuring in the thousa.TJ.ds of reels report that daily attention needs to be given to maintaining drive adjust-ment and tape cleanliness. (They report that the use of wraparound hanging seals and self-loading cartridges are
Cost savings with equivalent or superior per-formance characterize the plug-compatible tape drive market. The characteristics and prices of 48 models that can replace your I BM, Honeywell, and Univac magnetic tape units are presented in this report, along with straightforward buying guidance and users' ratings of 1,500 drives.
very helpful in maintaining cleanliness, and the use of outside services for cleaning tapes has also been men-tioned favorably.) Even if less attentive care results only in skipped areas on tape rather than data loss, much of the efficiency of high-performance drives can be lost through multiple retries and space loss. Such attention requires manpower that seemingly might be better used in other areas. And human nature is such that proper tape care is I:>
STC (Storage Technology Corporation) has emerged as the leading independent producer of high-performance magnetic tape drives.
The company has generated a strong financial position and a loyal group of well-satisfied users. STC's 6250-bpi Model 3670 tape drive, shown above, was the first independent unit to challenge IBM's state-of the-art advance in magnetic tape recording for computers. Not only is the performance very high (up to 1250K bytes per second), but the Group Coded Recording (GCR) method appears to provide superior reading of degraded tapes due to the more extensive e"or recover technique.
700-010-41 b Peripherals
All About Plug-Compatible Tape Drives 1:> often eliminated in the interest of developing new
applications. Consequently, high-performance tape drives can be greatly reduced in effectiveness.
Disk storage, on the other hand, requires less attention.
Performance degradation, although present, is not so evident as with magnetic tape. Convenience is a powerful incentive to going entirely with disk units-which are usually required anyway to accommodate new applica-tions and systems software.
What makes the disk/tape comparison more than an academic exercise is the existence of large tape libraries in many organizations. Conversion costs in terms of machine time, manpower, and media are substantial.
Tape drives will continue to be with us for some time to come. And while they are around, many vendors will provide attractive alternatives to the mainframe vendors' own offerings. The beginnings of the plug-compatible peripheral market are detailed in a companion Datapro report, All About Plug-Compatible Disk Drives (70D-OI0-40). The early emphasis in this market was on replacements for IBM magnetic tape drives; it has now . shifted to disk drive replacements. And there is a rudimentary market for plug-compatible peripheral pro-ducts for use with mainframes other than IBM's.
The Big Picture
There are a host of IBM tape drive models in the field-over 30 if you count the 729 models for the second-generation 1400 and 7000 series computers and the three new high-density models of the 3420. Everyone of these IBM models has been imitated by one or more manufacturers, and most of t}lese replacement drives are still on the market, although some of the older models are in limited supply. IBM System/360 and System/370 users are concentrating on two families of drives today: the low-performance, low-cost 3410/3411 family and the high-performance, high-cost 3420 family. Not surpris-ingly, these are the same families that are currently receiving maximum attention from the independents.
Accompanying this report are comparison charts showing the product lines offered by the independents. For your convenience in comparison, the IBM product lines are also shown. The IBM 729 family and its independent re-placements are not shown, however, because IBM has discontinued the availability of these units for new acquisitions. Replacements for the 729 drives can be obtained from Ampex, Potter, and Telex.
Not only have the independents produced tape drives with the same performance as the various IBM models, but they have plugged some gaps with additional models. This gives you a broad choice in selection but makes the decision more difficult; care in matching your needs with the performance of the various models will yield greater economy. To assist you in making your selection, the following table presents a set of "performance and storage
factors" for different combinations of block sizes and tape formats.
Performance and Storage Factors
Block size, Format, bytes per inch/interblock gap bytes 800/0.6 1600/0.6 6250/0.3
80 114.4 123.0 255.6
500 408.0 547.2 1318.8
1000 540.8 816.0 2175.0
2000 644.8 1081.6 3225.0
4000 714.4 1289.6 4256.3
Here's how to use these factors:
To determine a tape drive's effective transfer rate in bytes per second, multiply the appropriate factor by the tape speed in inches per second.
To determine a tape reel's storage capacity in bytes, multiple the appropriate factor by the tape length in inches.
The State of the Market
An overall view of the plug-compatible market (or PCM, as it is now frequently called) is presented in the companion report on plug-compatible disk drives im-mediately preceding this report.
The legal problems for plug-compatible manufacturers in com bination with the waning importance of magnetic tape have caused some changes in the tape drive market.
Some formerly significant vendors are not present in this year's charts, inclUding Texas Instruments and CIG.
Ampex, an early leader in the field, has cut back its end-user marketing efforts, and Potter's well-publicized financial difficulties had not been resolved at press time.
One new vendor has been added: Formation, which supplies tape units for Honeywell and Univac mainframes.
STC (Storage Technology Corporation) has emerged as the leader in the field of high-performance tape drives among the independents, and is doing very well indeed.
Telex maintains a strong installed position, and CalComp also makes its presence known in the market.
Companies that study computer markets, such as Inter-national Data Corporation (lDC), are not optimistic about the growth of the plug-compatible field. And tape drives are more vulnerable than disk drives. The future of the market may well depend on the outcome of pending legal suits as much as on marketing and technical develop-ments. PCM is seen by market researchers as only a small portion of the overall independent peripherals market (lDC estimates 30 percent), which is considered to have
sizable positive growth potential. ~
©1975 DATAPRO RESEARCH CORPORATION, DELRAN, N.J. 08075 REPRODUCTION PROHIBITED
MAY 1975
700-o10-41c Peripherals
All Abottt Plug-Compatible Tape Drives
USERS' RATINGS OF MAGNETIC TAPE DRiVES
Number Number Weighted Averages and Response Counts** Problem Counts**
Magnetic Tape Drive of User of Drives Overall Ease of HardW111'8 Maintenance
Installation Operation Re- Rep. Perforlft1lllC8 Operation Reliability Service
sponses resented
WA ~ G FI f WA E G FP WA E G F P WA E G F P None Min Maj. None Min Maj.
IBM 2401 5 11 2.8 o 4 110 3.0 c 50 o 2.6 0 3 2 0 3.3 2 1 1 0 1 3 1 2 1 1 IBM 2401 Replacements:
Ampex 1624 series 3 18 2.3 0 2 o 1 3.5 1 1 100 1.5 0 0 1 1 2.0 0 0 20 0 2 1 1 2 0 Potter/MAl 2400 series*** 18 143 25 1 8 a 1 2.7 4 9 41 2.3 2 5 7 4 2.1 1 4 84 5
I
9 3 1 1
6 9
Telex 4862 10
I
35 3.1 3 4~I~
3.2 3 5 1 0 2.81 2 412 1 2.8 31 2 3 1 6 2 2 5 4 0 Texas Instruments 924 3 10 27 1 0 4.0 1 0 00 4.0 1 o 0 0 4.0 1 0 00 0 3 0 0 3 0 Subtotals, independents 34 206 2.7 514 12 2 3.1 E 15 51 2.4 5 910 6 2.4 5 6 135 11 16 6 7 15 9 IBM 3410/3411 2 5 3.5 1 1 0 fo 3.0 C 20 o 3.5 1 1 0 0 3.5 1 1 00 1 1 0 2 0 0 IBM 3410/3411 Replacements:Telex 6410/6411 2 4 25 0 1 1 0 3.0 1 o 1 o 1.5 0 0 1 1 2.0 0 1 o 1 0 2 0 0 1 1 IBM 3420 17 158 3.7 12 5 0 10 3.6 11 60 o 3.6 10 7 0 0 3.5 8 9 00 11 5 1 7 6 0 IBM 3420 Replacements:
CaIComp345 12 47 29 4 4 3 1 3.5 6 60 o 2.6 3 5 0 4 3.1 5 3 40 5 2 3 4 3 6 Control Data 34201 5 26 3.2 2 2 1 0 3.6 3 20 03.0 1 3 1 0 2.8 0 4 1 0 0 2 3 2 3 0 Mohawk 8420 4 31 3.3 2 1 110 3.5 3 01 03.7 2 1 0 0 3.5 2 2 00 2 2 0 1 3 0 Potter 2 13 25 0 1 1 0 3.5 1 1 0 02.5 0 1 1 0 3.0 0 2 00 1 1 0 1 1 0
STC-3430 12 115 3.9 11 1 0 o 3.9 11 1 0 o 3.8 9 3 0 0 3.6 7 5 00 9 3 0 10
I
2 0 3450 16 188 3.8 13 3 0 1,0 3.8 13 30 03.5 9 6 1 0 3.5 9 6 1 0 4 11 0 10 5 0 3470 9 131 3.7 6 3 0 o 3.9 E 1 0 03.6 6 2 1 0 3.6 5 3 00 4
I 5 1 6 3 1
3650 3 64 4.0 2 o 0 03.5 1 1 0 04.0 2 0 0 0 4.0 2 0 00 0
I 2 0 0 2 0
Other STC drives 9 360 3.6 5 4 00 3.3 3 60 o 3.4 4 5 0 0 3.3 4 4 1 0 2 7 0 2 7 0 Telex 6420 series 18 143 2.8 210 60 3.6 11 70 o 2.6 3 6 7 2 2.6 3 7 62 5 I
9 4 6 6 6 Subtotals, independents 90 1,118 3.4 47 29 121 3.7 6e 28 1 0 3.2 39 32 11 6 3.2 37 36 132 32 44 11 42 35 13 Totals by Vendor:
Ampex 3 18 2.3 0 2 01 3.5 1 1 0 o 1.5 0 0 1 1 2.0 0 0 20 0 2 1 1 2 0 CaIComp 12 47 2.9 4 4 31 3.5 6 60 o 2.6 3 5 0 4 3.1 5 3 40 5 2 3 4 3 6 Control Data 5 26 3.2 2 2 10 3.6 3 20 03.0 1 3 1 0 2.8 0 4 1 0 0 2 3 2 3 0
Mohawk 4 31 3.3 2 1 1 0 3.5 3 01 03.7 2 1 0 0 3.5 2 2 00 2 2 0 1 3 0
Potter 20 156 2.5 1 9 9 1 3.0 510 4 1 2.3 2 6 8 4 2.2 1 6 84 6 10 3 2 7 9 STC 49 858 3.8 37 11 00 3.8 36 12 00 3.6 30 16 2 0 3.5 27 18 20 19 28 1 28 19 1 Telex 30 182 2.9 515 9,0 3.4 1512 20 2.6 510 10 4 2.6 6 10 94 11 13 6 11 11 7 Texas Instruments 3 10 2.7 1 0 20 4.0 1 00 04.0 1 0 0 0 4.0 1 0 00 0 3 0 0 3 0 Subtotals, independents 126 1,328 3.2 52 44 ~ 3 3.5 7043 7 1 3.0 44 41 22 13 3.0 42 43 268 43 62 17 49 51 23 IBM Totals 24 174 3.5 1310 1 0 3.5 11 13 00 3.4 11 11 2 0 3.4 11 11 1 0 13 9 2 11 11 1 Grand Totals 150 1,502 3.2 65 54 ~ 3 3.5 81 56 7 1 3.0 55 52 24 13 3.1 5354 278 56 71 19 60 62 24
* All Response Counts are expressed in terms of the number of user responses. The legend is E for Excellent, G for Good, F for Fair, and P for Poor. The Weighted Averages (WA) are derived by giving each response equal weight and assigning a numerical value of 4 (Excellent), 3 (Good), 2 (Fair), or 1 (Poor) to each rating.
"Cross totals may not sum to the number of responses because not all responses included a rating in every category.
** All Problem Counts are expressed in terms of the number of user responses. The legend is Min. for Minor and Maj. for Major. Cross totals may not sum to the number of responses because not all responses included a reply in every category.
~ User Experience
Part of any conscientious selection program is talking with existing users of the "products under consideration. To assess the current level of user satisfaction with plug-compatible tape drives, Datapro recently conducted an extensive survey of its subscribers. A Reader Survey Form was included in the February 1975 Supplement to Datapro 70 and mailed to all subscribers. By April 10, usable responses had been received giving experience with 126 different cases, representing a total of 1,328 in-dependently supplied tape drives. In addition, we elicited 24 responses representing experience with 174 IBM tape drives.
Users were asked to rate their tape drives in four categories: Overall Performance, Ease of Operation, Hardware Reliability, and Maintenance Service. In addi-tion, they were asked to indicate any problems
en-countered in the installation and/or operation of the tape drives.
The results are presented in the accompanying table; with the footnotes, the table is self-explanatory. A further analysis of the Problem Counts is useful, however. On a percentage basis, the users' experience with independent drives breaks down this way:
Installation Problems:
None-35%
Minor-51%
Major-14%
Operational Problems:
None-4O%
Minor-41%
Major-19%
700-010-41 d Peripherals
All About Plug-Compatible Tape Drives
The early leader in the plug-com-patible disk drive marketplace, Telex has used much of its energies in recent months to pursue legal action against IBM. The Telex 6420 drives shown here are replacements for IBM's 3420 line.
t:>
Negative comments by the users centered mainly on controller problems and field service personnel. Positive comments were almost exclusively of the type: "It works and is cheaper than IBM's."How to Buy
The comparison charts tell you what is available. The users' responses tell you about others' experience with particular equipment. But this is not enough. You need a logical plan to help you determine: (l) whether to replace your tape drives with equipment from one of the independents, (2) which drives to select if you decide to go ahead, and (3) how to implement that selection.
The preceding report, All About Plug-Compatible Disk Drives (70D-OJ 0-40), contains a detailed discussion of just such a plan of attack. Summarized, it goes like this:
• Re-examine your installation to see how many of which tape drives you really need.
• Survey the field to find the devices that are suitable for your needs and available (with full maintenance ser-vice) in your area. Sending a request for proposals to the pertinent vendors is a good way to tie down exactly what each vendor is willing to do for you, and may help to reduce the cost if each vendor knows he is in a competitive bidding position.
• Analyze all costs (equipment, installation, and main-tenance) and anticipated savings.
• Investigate the alternatives-including outright pur-chase or purpur-chase/leaseback of your present IBM equipment and the three ways of acquiring indepen-dent peripherals (one-year lease, long-term lease, or purchase).
• Assure yourself of the reliability of the equipment by checking the supplier's reputation, talking to other users, and/or testing the equipment in your installa-tion.
• Choose the equipment that offers the lowest overall costs while meeting your requirements for availability, reliability, and maintenance.
• Negotiate a sound contract. Be sure to spell out exactly what the vendor is responsible for and what you are taking the responsibility for.
Plug-Compatible Tape Drive Characteristics The accompanying comparison charts summarize the characteristics of 48 commercially available tape drives for replacing IBM, Honeywell, and Univac tape units. The information was supplied by the manufacturers during the months of March and April 1975. Their cooperation is acknowledged and greatly appreciated.
The chart entries and their significance are explained in the following paragraphs.
Each model of each family is listed separately to permit better presentation of format options and cost informa-tion.
When a designated model of an independent drive is an exact replacement, in terms of format and speed, for a particular IBM or other model, the manufacturer and model number are stated. Some models of the indepen-dent drives are not exact replacements, having a tape speed that falls between the values for two IBM models.
For such units, no IBM model is designated. Within families of tape drives (e.g., the IBM 3420 family of six drives), different models can normally be intermixed on t:
©1975 DATAPRO RESEARCH CORPORATION, DELRAN, N.J. 08075 REPRODUCTION PROHIBITED
MAY 1975
700-01 0-41 e Peripherals
All About Plug-Compatible Tape Drives 1:::> the same controller if appropriate density and format
features are added. In addition, do not lose sight of the fact that lower- and higher-speed models constitute valid replacements for a particular IBM model as long as you stay in the same family. To go to a different family, a different controller is generally required.
Configuration
The method of attaching the drives to the mainframe is clearly stated. If the drives can be attached via the mainframe vendor's controller, the controller model number is stated. If the independent drive manufacturer also markets a controller, it is identified. If only one methods is specified in the charts, this identifies restric-tions on whose controller you can or must use.
Controller switch options provide a capability that used to be called "pooling." This permits a degree of flexibility by switching a group of drives among several controllers. In a mixed-format or mixed-speed environment, controller switch options permit reconfiguration to take advantage of the computer's input/output paths. Conventional notation of the form 2 x 16 identifies the number of controllers that can be in the switch group (the first number) and the maximum number of drives that can be switched (the second number).
Ozannel switch options permits a tape subsystem (con-troller plus attached drives) to be switched under program control between multiple processors. Tape subsystems are expensive. Definite operating economies can sometimes be achieved by sharing tapes among multiple processors in the same facility. With disk units, such a switch is frequently attractive in implementing a data base. For tape, it is primarily an economy feature where full-time tape drives are not required on each processor.
Recording Characteristics
Each combination of formats-the number of tracks and the recording density -is listed separately for each model.
The almost universal acceptance and adherence to IBM-established recording practices permits great shortcuts to be taken in what could otherwise be a difficult technical discussion. The four accepted standards are:
• 7-track, 200, 556, and/or 800 bits per inch
• 9-track, 800 bits per inch
• 9-track, 1600 bits per inch
• 9-track, 6250 bits per inch
The 7 -track format is a carry-over from second-generation IBM computers. It was superseded when IBM introduced the System/360, which is oriented toward an eight-bit data character (byte). However, some users have not converted all their fues. The 7-track capability is retained for exactly the same reason that emulation of the IBM 1400 and 7000 series computers is retained.
Terms such as NRZI (non-return to zero on ones), PE (phase encoded), and GCR (group coded recording, IBM's latest) are great for impressing your friends as to the extent of your knowledge about electronic and magnetic phenomena, but are unnecessary. All the independents adhere to IBM's standards. However, this does not guarantee in and of itself that the tapes recorded on an IBM drive can be read on an independent drive, nor the converse. It does not even guarantee that tapes recorded on one drive can be read by another drive in the same subsystem. This is where your maintenance personnel come into the picture. All drives that use a particular ~
Users of non-IBM computer systems have long looked at the plug-com-patible peripheral market with envious eyes. Formation, among others, is doing something about it.
The tape subsystem at left is directed toward Honeywell computer users.
Formation also serves the Univac/
RCA user.
MAY 1975 ©1975 DATAPRO RESEARCH CORPORATION, DELRAN, N.J. 08075
700-010-41f Peripherals
All About Plug-Compatible Tape Drives I::> recording format can normally be adjusted to be
com-patible with one another, but you may have to request or demand it specifically. If this type of compatibility is critical to your operations, it is a worthwhile point to include in the contract.
Features
The availability of certain features is spelled out clearly for all tape drives listed. Simultaneous read/write and read backward features are self-explanatory. Mode compati-bility permits mixing 7- and 9-track tape drives on the same controller.
Performance
Tape speed and transfer rate are self-explanatory. The rewind time is also self-evident, but its effect is sometimes overlooked in estimating performance. As it affects performance, rewind time corresponds to the stop time of a disk pack drive. Its importance is a direct function of the frequency with which you change tape reels.
The tape slack buffer entry identifies the technique used for managing the length of tape pulled off the tape reel ahead of reading or writing. This is a necessary operation for reducing the time it takes to bring the tape up to
The tape slack buffer entry identifies the technique used for managing the length of tape pulled off the tape reel ahead of reading or writing. This is a necessary operation for reducing the time it takes to bring the tape up to