The following is the text of an IBM Data Processing Division technical press release distributed on October 9, 1974.


IBM 3850 Extends Virtual Concept To Online Storage Units, Expands Capacity, Processing Power For Large Data Base Users

The IBM 3850 mass storage system, announced today, offers a new concept in information storage -- the IBM Data Cartridge -- that combines the random access characteristic of disk devices and the economy of tape drives.

With the data cartridge as its basic component, the new system features capacities from 35 billion to 472 billion characters of information -- equivalent to or larger than most extensive tape libraries. At the same time, the economical system can reduce a user's cost per million characters to as little as one-tenth the cost of online magnetic disk storage. Additionally, the 3850 enables users to achieve new levels of data and device utilization by extending the virtual storage concept to magnetic disk devices.

The components of the 3850 mass storage system are the new data cartridges, the IBM 3851 mass storage facility, the new IBM 3830 storage control Model 3 and the widely used 3330-series disk subsystem.

Compact Data Cartridge

A combination of magnetic tape and disk storage techniques, the new two-by-four-inch plastic cartridge holds 50 million characters of information. The data is stored on a spool of tape approximately three inches wide and 770 inches long.

Information on the tape spool is organized into cylinders in much the same way it is recorded on magnetic disks, giving the tape medium the random access characteristic of disk storage.

Each cylinder is recorded at a fixed location, and specific cylinders can be located by identifiers along the edge of the tape. Each cartridge can contain 202 cylinders of data.

Two cartridges are called a "mass storage volume," just as tape volume and disk volume identify a tape reel and disk pack. One mass storage volume has 404 cylinders, 19 tracks per cylinder, and a maximum of 13,030 characters per track. Thus, two data cartridges are the storage equivalent of one 3336 Model 1 disk pack -- 100 million characters of information.

Versatile Mass Storage Facility

The 3851 mass storage facility is linked to both a virtual storage IBM System/370 and a 3830 disk control unit. It houses the cartridge storage space allowing users to keep all their information online to the computer. For example, a system with two mass storage facilities can house as much as 472 billion characters of information -- equal to a typical tape library of 47,200 reels of tape, storing an average of 10 million characters each, or 4,720 3336 disk packs.

Major elements of the 3851 are:

The Mass Storage Control also is part of the 3851 facility. It provides overall control for the mass storage system's functions, including the transmittal of information between the facility and disk storage.

The mass storage control's other major tasks include:

There are two series -- A and B Models -- of the 3851. Each series has four models of the device with a minimum capacity of 35.3 billion characters of information. The 385l's B Models provide an additional mass storage control for backup operations.

3851 Mass
Storage Facility Models:
A1,B1 A2,B2 A3,B3 A4,B4
Character Capacity (Billions) 35.3 102.2 169.1 236
Data Cartridge Capacity 706 2,044 3,382 4,720
Mass Storage Volumes 353 1,002 1,691 2,360
Accessors 2 2 2 2
Data Recording Controls 1 2 3 4
Data Recording Devices 2 4 6 8

New 3830 Model 3 Storage Control

The storage control monitors the transfer of data between the 3330-series disk subsystem and the System/370. It is equipped with a buffer storage that allows it simultaneously to transfer data with both the mass storage facility and the computer.

The optional Staging Adapter Feature available with the 3850 system enables the integrated storage controls on the System/370 Models 158 and 168 to perform the same functions as the new 3830 Model 3.

Virtual Drive Concept

The system's "virtual" disk drives can enable the mass storage user to process more jobs at the same time than with conventional magnetic tape and disk storage devices. The virtual drive capability creates the image of many disk drives, just as IBM's virtual storage programming uses a System/370's main memory as though it were much larger than it actually is.

This technique is implemented as the 3830 continuously exchanges data with the mass storage facility and reuses space on disk packs -- eliminating the need to dedicate disk storage space to a single file.

For example, up to 32 disk drives may be attached to a 3830 storage control. Up to 16 of these may be designated virtual, or "staging" drives -- to which data from the mass storage facility's cartridges is transferred.

The 3830 creates virtual storage space on these 16 drives by allocating multiple addresses to the group of staging drives. The storage control can address information to as many as 64 units, regardless of how many real disk drives are attached. Thus, if the maximum of 32 drives is attached, the 3830 can manage them as though disk capacity had doubled. The status and location of information in staging drives are maintained in both the mass storage control and the 3830.

New or modified data from the staging drives is "destaged," or automatically returned to the data cartridges. If no change has been made to the information, it need not be returned to mass storage -- since the original record has been retained in the data cartridges -- but can remain on the disk where it is available for immediate reuse.

The non-staging disk drives also can be used for data communications applications -- such as interactive teleprocessing -- that require more frequent access to information.

System Reliability

The 3850 can give users higher levels of storage system reliability, and serviceability in these areas:

Programming Support

The 3850 mass storage system operates with IBM's System/370 Models 145 through 168 running under Operating System/Virtual Storage 1 or 2 (OS/VS1 or 2) Whenever computer programming requires mass storage system functions, a new part of OS/VS -- the Mass Storage System Communicator -- will issue the appropriate commands to the mass storage control. This includes the ability to mount a mass storage volume on a disk and to destage an application data set.

Additionally, options have been added to Virtual Storage Access Method (VSAM), giving the user a selection of different staging and destaging procedures.

Data Security

Physical security of the 3850 is enhanced by keeping all data in one place - - the 3851 storage facility -- under the continuous control of system programming.

Access to information in the 3851 is controlled through existing OS/VS 1 and OS/VS2 password protection programming. This optional capability limits access to data sets and controls the use of utility commands.

To ensure that a mass storage data set is no longer accessible once a job is processed, an optionally available feature of VSAM can cause disk-resident data to be written over with zeros. A read-only feature, another VSAM option, can prevent the writing of data in a volume.

To reinforce physical security measures, a user may place locks on all 3850 access panels. Additionally, the system can be equipped with special features to detect the presence of any foreign magnetic device, to sense fire and fumes and to trigger a user-supplied fire suppression system.

Further, the 3850 may be located as far as 200 feet from the central computer, allowing users to install it in special security areas.

Prices and Availability

First customer shipments of the 3850 mass storage system as well as the staging adapter feature for the Models 158 and 168 are scheduled to begin in the third quarter of 1975. Field conversions of existing 3830 storage control units and Models 158 and 168 also are scheduled to begin in the third quarter of 1975.

The 3851 mass storage facility is available under IBM's Extended Term Plan (ETP), which provides for a two-year contract period, for monthly rentals ranging from $10,600 for a minimum-capacity model to $51,200 for a 472-billion character configuration with two mass storage facilities. Under the standard IBM agreement, monthly rental ranges from $12,455 to $60,160. Purchase prices will range from $477,000 to $2,304,000.

The 3830 Model 3 storage control is available under IBM's Fixed Term Plan for a one-year contract period with a monthly rental of $3,901. FTP rental for the Model 3 is $3,562. Under the standard IBM agreement, rental is $4,240. Purchase price is $160,000.

The data cartridges are available for purchase at $20 each.

The 3850 mass storage system was developed by IBM's General Products Division (GPD) in Boulder, Colorado, where it will be manufactured. It also will be manufactured at IBM facilities in Mainz, Germany. GPD developed the 3830 Model 3 at its facilities in San Jose, California, where the device will be manufactured.


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