THE APPLICATION OF CRAM

Specifications alone cannot adequately portray the facts about any computer configu-ration. This is especially true if such a con-figuration involves new concepts. This sec-tion will explain how the 315-CRAM System copes with widely dissimilar applications.

Instead of Singling out any particular applica-tion (although specific instances will be cited) the capabilities of CRAM will be discussed in two generalized areas: 1) file updating and 2) sorting. For clarity, analogies will be

Card Random Access Memory (Cram): Functions & Use / 151 drawn with tape systems and current random

access systems so as to underscore certain efficiencies, economies, and flexibilities of the 315-CRAMSystem. All performance fig-ures will be compared with a 315-tape system.

The prime factor in determining final per-formance of data processing systems is the organization and basic efficiency of the sec-0ndary storage devices. Usually the type of device chosen for secondary storage (tapes, disc, drum, or cards) determines the appli-cations areas for which it is best suited. In-formation storage requirements may change completely from one application (or one part of an application) to another. The information storage flexibility of the CRAM and its at-tendant efficiency are its greatest assets. A single CRAM unit combines the abilities of contemporary random access devices and magnetic tape handlers. The flexibility of CRAM makes it possibleto have a single type of secondary storage peripheral which eco-nomically satisfies all data processing re-quirements. To exemplify CRAM's flexibility, its use for file updating will be outlined.

1. File Updating

The general file updating process consid-ered here will be that which is standard for typical business data processing. A Mast~r

Historical File must be posted and updated for each transaction which has been input into the system. Three basic techniques of up-dating may be used efficiently in 315 installa-tions, vis., Random, Serial Selective and Serial Copy. Most data processing problems, however, do not require clear cut versions of any of these. The CRAM permits the use of techniques which skillfully blend these methods into an optimally efficient system.

a. Random Access (Figure 4)

The CRAM provides the 315 with anexcep-tional random access memory. Maximum access time of 200 milliseconds, a reaccess time of 15 ms, the ability to store 5,555,200 characters on each CRAM unit,and the 315's potential of controlling 16 such units each with independent access, all attest to this statement. The ability to change CRAM memory cartridges in apprOximately 30 sec-0nds make CRAM unique for a device of its capabilities. This makes it possible to seg-ment storage allocations in such a manner

Figure 4

that information pertinent to separate random access jobs can be loaded as required.

In order for other known random access systems to accomplish the same function, information must be unloaded to another stor-age medium, e.g., tapes or cards. Since this technique unnecessarily burdens the system the alternative approach is usually taken of providing enough storage capacity for all jobs which will use the memory. The prevailing concept of "immobile information" therefore turns out to be an expensive restriction which is obviated by the CRAM file replaceability concept.

It should be noted that this concept not only provides for efficient utilization of secondary storage capacity, but also provides for back-up should one of the units become inop-erative. The cartridge on that unit can easily be removed and mounted on a spare unit, thus making the data once again available to the system with a minimum of down time.

For random file proceSSing, commonly used addressing methods are employed to select a CRAM unit, drop a card and then read a track. These methods include the use of d ire c tor i e s, direct add res sin g, or

152 / Computers - Key to Total Systems Control calculated addresses. When the appropriate track is read it is scanned by the program for the proper logical record. Storage over-flow methods are incorporated if the record being sought or written could not be stored on the selected track. Methods of address selection and storage overflow control are conventional and will not be described here.

The appropriate track of the selected card is available for reading 200 ms. after the card has been called. This track is read in 31 ms.

As was explained earlier, the card remains rotating on the drum and 15 ms. elapse before the card can again be read or written upon.

During this 15 ms. the record in the track can be found by program and in most cases updated (the 315 is a fast computer with an average command execution time of 50 u sec).

The card can then be written on in 31 ms.

during its next revolution. If for any reason the updating takes over 15 ms., the recording of the updated record can be performed on subsequent revolutions since the card remains on the drum effectively until released or until another card is dropped. This procedure applies as well to the case where a second track of the same card must be read as in the case of storage overflow. During the writing of the updated track, a second card may be accessed and dropped on the same unit. When cards are being dropped simultaneously on separate units, the program is advised by interrupt when a card is ready to be read or written.

The net time to randomly update a file stored on one CRAM is approximately 4 transactions per second. When the file is stored on multiple CRAMs and cards dropped simultaneously, this speed approaches 13 transactions every second.

b. Serial Selective Updating (Figure 5) The serial selective file updating technique is actually a modification of the random up-dating technique. As in random processing, track directories, as well as storage over-flow methods, are employed to facilitate rec-ord addressing. In this method, the entire Master File is sequenced and stored over one or several CRAM cartridges. Transactions are sorted into Master File sequence and posting to active cards and active tracks takes place selectively, i.e., those cards and tracks which are not affected by transactions are left undisturbed; those cards and tracks which

Figure 5

are affected are read, updated in memory, and recorded over the old information.

This method, while requiring batch proc-eSSing, has two definite advantages over ran-dom processes. The number of cards which must be dropped and the number of tracks which must be read and written is never more then the number of cards and tracks which must be updated. Secondly, the entire Master File need not be available to the computer at one time. As the file is being processed serially, a single CRAM unit (or two if alter-nation is desired) is sufficient regardless of the magnitude of the file. The first cartridge of the file is mounted, updated, and replaced by a second and so on through the file.

For low activity files, this method of up-dating provides the most efficient utilization of CRAM. For instance, if the average num-ber of active records is one per card, the 315 to match this performance would require tapes which operate effectively at 236,000 characters per second with no start and stop time. Even for a moderately high activity averaging one transaction per track (typically a track contains 5 to 15 logical records), the effective 315 tape rate would have to be 77,000

Card Random Access Memory (Cram): Functions & Use / 153 characters per second. With current stop

start times and assuming blocking similar to CRAM, 315 tapes (which are generally simi-lar to other tape systems) would need to operate at over 100 kc to achieve such an effective rate. The net updating time per transaction (one to a track) using this serial selective CRAM method of updating and em-ploying a single CRAM is 12 transactions per second.

In practice it is often found that the very low activity files are by their nature quite extensive. This leads to the problem of on one hand requiring a random access devised to achieve fast processing and on the other hand requiring mass storage devices such as tapes to inexpensively store the files. How-ever, random access devices are uneconom-ical in storing data and tapes are inefficient in processing low activity files.

The serial selecting updating method in conjunction with the CRAM's fast access and interchangeable file concept provides an effi-cient solution to the problem.

c. Serial Copy Updating

The CRAM unit can also be used exactly like an ordinary magnetic tape handler. Each cartridge can be considered a tape reel stor-ing 1792 blocks (tracks of cards) each of which stores up to 3100 alphanumeric char-acters or 4650 numeric digits. All CRAM tracks are then considered sequentially in this method. Master Files can be organized for conventional Father-Son (Copy) updating.

In this method the file is sequenced, as are all transactions which must be posted against the file. The old (Yesterday's) Master File is read, all active records updated and a com-pletely current New Master File written. In such a method of file updating, all tracks of all cards on the Old Master File must be read while all tracks (as updated) of all cards are written on the New Master File. Usually this method employs two CRAMs (an old and new) or four if cartridge change time is to be shared. With such a method, those files which lend themselves best to Magnetic Tape File Processing can be handled at least as effi-ciently with CRAMs. All the features of re-taining yesterday's files for emergencies, the handling of high activity files where records are being added, deleted, and changed in size are retained with CRAM, identically as with tapes.

The efficiency of such a system is out-standing. Using but one read in and one write-out memory area, the time to copy a single access times can be eliminated. While proc-essing information in buffer 2, the interrupt is set to advise the read and write macros Demand Deposit Accounting application for banks. The characteristics of a checking account file are high activity, and constantly changing record sizes. These requirements are satisfied by such a Father-Son updating technique with CRAM.

Added Considerations of CRAM file Proc-essing

i. Control

Although the random or Serial Selec-tive method may be used for a given applica-tion, the need for periodic sequential proc-essing is ever present. Such activities as insertion of new records, deletion of old, creation of rescue \ files or file dumps all require sequential file access. These activ-ities on conventional random access devices are expensive, time consuming, and often re-quire that additional non - homogeneous equip-ment such as tape units be included in the system. The CRAM, on the other hand, can-not only execute these periodic operations efficiently, but can actually create sequential expanding files, such as transaction files, while doing random proceSSing. This ability plus the discreet nature of the CRAM file permitting direct access to the affected por-tion of the file greatly facilitates reconstruc-tion and the maintenance of audit trails.

Such blending of several techniques but always using the same peripheral CRAM pro-vides high efficiency with safety without in-creasing the peripheral requirements of an installation.

154 / Computers - Key to Total Systems Control ii. Absence of Rewind

Whenever the CRAM is being used in a magnetic tape fashion there is one major feature of CRAM which cannot be overlooked.

Rewind is completely eliminated. Time be-tween jobs is appreciably reduced. On com-pletion of a run, CRAM can be changed im-mediately whereas tapes are required to be rewound. Many applications require multi-tape reel or multi-cartridge files. In multi-tape

systems the lack of an alternate handler in-volves the loss of both reel rewind as well as reel changing ~imes. Since only cartridge change time is involved in CRAM systems, the requirement for alternate C RAM. units is less severe.

iii. Multi File Cartridge

Not only do multiple CRAM cartridges make up a single file but each cartridge can also be used to store multiple small files.

For instance, cards 2-70 can store the Program File, cards 71-130 a Transac-tion File, 131-200 an Output File, and 201-255 a temporary working file (Figure 6).

Searching and in most cases recording

Figure 6

restrictions on magnetic tape make such multi file tape reels very difficult and cum-bersome to work with at best. The importance of being able to organize file data in this manner is readily apparent. Applications using such small files usually require more time between runs to accomplish tape set ups than they do for processing. Much of this set up time can be eliminated by properly pool-ing multi files on one or two CRAM cartridges.

In many applications several tape processing runs may be combined into a single CRAM run because of the availability of all necessary files at one time. With CRAM such consolidation can become natural with proper information organization.

Fewer CRAM units are required to do a particular job. A typical example isNCR's own COBOL translator which requires a minimum of six tape handlers. Using the exact same system organization but allowing each CRAM to be segmented into multi files, COBOL will require but two CRAM's for translation (with a speed increase over our 315 tape system). With some loss of effi-ciency, COBOL will later be coded to run on one CRAM.

d. Summary

For file updating the 315 CRAM System offers a versatility of file organization. Any one of three normally acceptable file methods can be employed with high efficiency and all on the same unit. Numerous advantages are possible with CRAM over older peripherals, all of which were designed with but a single method of file maintenance in mind.

2. Sorting

Besides file updating another major data processing operation is sorting. Sorting ca-pabilities are, and should be a major test of equipment. Even on a randomly posted file, the sorting of output and of various oth,er auxiliary files is of prime importance. The sorting capabilities of the CRAM are excep-tional. Methods outlined here are straight-forward. The basic concept is to divide the CRAM or CRAMs into four logical files. Sort-ing is then accomplished exactly as if a four tape sort were being performed. Much of the logic of the 315-tape sort generator is car-ried over directly to a 315-CRAM sort gen-erator which will produce programs USing 1,

Card Random Access Memory (Cram): Functions & Use / 155 2, or 4 CRAMs. The following table indicates

the effectiveness of CRAMs versus tapes.

Time required to sort 30,000 records on internal sort times are identical for tape or CRAM. Tape times, however, are decreased by 43% and 66% respectively for 2 or 4 CRAM sorts.

Such savings are achieved by the CRAM's capabilities of sharing card drop and trans-ferring information at very high rates. In addition, the CRAM is not encumbered with start-stop and rewind times as are tapes.

As well as e m p loy i n g straightforward techniques in the CRAM sort generator, more advanced methods can be devised to make full use of the CRAM's capabilities. One of these techniques takes advantage of the CRAM's ability to handle each track as a separate logical tape. Byusing a combination of block sorting techniques and then conventional merging techniques, the number of passes through the data to be sorted is reduced. This, of course, reduces the total sorting time from those figures mentioned above.

For the basic needs of data processing applications, the unique features of the CRAM proved exceptional in all studies. Not only is basic efficiency, with flexibility of ap-proach, inherent in CRAM but the wide range of small CRAM-315 to large CRAM-315 sys-tems allows National to enter a wide scope of application areas with one computer. Systems employing as few as one CRAM and as many as sixteen are valid and efficient (depending on the job). Increased capabilities are readily achieved as CRAM units and memory modules are added to a smaller CRAM-315 System.

The hardware capabilities of the CRAM ha ve been outlined as have many of its general uses. However, the CRAM picture would not be complete without also describing the soft-ware programs provided with the system.