I believe the 1405 had a single arm that carried a read write head that was used on all platters,....had to move up dand down for each platter as well as in and out....
20th century disk storage chronology
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1956
IBM introduces the 350 RAMAC, the first computer disk storage system. In less than a second, the 350 RAMAC's "random access" arm retrieves data stored on any of 50 spinning disks. Disk technology later becomes the industry's basic storage medium for online transaction processing.
1962
The IBM 1311 is the first storage unit with removable disks. Each "disk pack" holds more than two million characters of information. Users can easily switch files for different applications.
1965
Database and data communications applications requiring access to large amounts of information - such as airline reservations and online banking transactions - become economically feasible with the IBM 2314 Direct Access Storage Facility.
1970
With the IBM 3330, servo feedback technology makes it possible to record data on disks more densely than ever before. Error-correction coding increases the availability of data and the efficiency of the manufacturing process.
1971
IBM introduces the industry's first flexible magnetic disk, or diskette. The "floppy disk" greatly increases the convenience of data handling. It becomes widely used as a basic storage medium for small systems.
1974
The IBM 3340 disk drive introduces an advanced head and disk technology known as "Winchester." The 3340 features a small, lighter read/write head that rides closer to the disk surface - on an air film 18 millionths of an inch thick. The 3340 doubles the information density of IBM disks to nearly 1.7 million bits per square inch.
1980
IBM introduces "thin film" head technology, which enables the 3380 Direct Access Storage Device (DASD) to read and write data at three million characters per second. It is the first commercial unit to achieve such a rate. The thin-film read-write head of the IBM 3380 disk drive "flies" 12 millionths of an inch over the disk surface. This is comparable to a large plane flying 1/20th of an inch over a lake's surface without touching the water.
1981
High-performance "cache" memory is introduced with the 3880 Storage Control. The 3880 moves frequently used data from disk storage into semiconductor storage for high-speed access by the processor. Cache is an advanced, integrated system approach that uses both hardware and software.
1985
The IBM 3380 D/E DASD are introduced. The 3380E offers five gigabytes of storage capacity and is the largest capacity DASD of its time.
1987
Storage subsystem synergy acquires new meaning with the introduction of the triple-capacity 3380 DASD Models J and K and the 3990 Storage Control. The 3380 J/K DASD and the 3990 Models 2 and 3 deliver yet another DASD innovation: four-path data transfer. Extended control unit functions also include DASD fast-write and dual copy.
1989
The IBM 3390 Model 2 increases the capacity of a single DASD box to 22.7 gigabytes (22.7 billion bytes) and the throughput to 40 percent over the IBM 3380K.
1991
The 3390 DASD Model 3 increases the capacity of a single DASD unit to 34 gigabytes and offers up to 180 gigabytes in a 3990/3390 Storage Subsystem.
The new family of rack-mounted, CKD 9340 DASD Subsystems addresses the requirements of intermediate computing environments. The entry-level 9341/9345 connects to a 9221 processor and stores 2-24 gigabytes of information while the 9343/9345 stores 4-48 gigabytes and can take advantage of ESCON.
1992
IBM introduces one of the first 3.5-inch disk drives on the market to offer up to 1.2 billion bytes of storage - enough capacity to store more than a half million pages of typewritten information; the first 2-gigabyte 3.5-inch disk drive and the first 4-gigabyte 5.25-inch disk drive for the original equipment manufacturers market. IBM ships more than 250,000 1-gigabyte 3.5-inch hard drives in 1992.
1993
IBM announces and begins delivering a host of new products, ranging from lower cost storage options to new subsystems capable of storing three times the amount of data as previous models. These product introductions include: new disk storage systems for use with the AS/400; five additions to its line of disk drives and storage subsystems for the original equipment manufacturer marketplace; new 200 Series models of the 9337 Disk Array Subsystem; a selection of disk storage products for users of RISC System/6000 POWERservers and POWERstations; and introduction of the industry's first high-capacity drives for the portable computing market using new magneto-resistive head technology.
In addition, IBM announces that it has increased the throughput of the 3990/3390 Storage Subsystem up to 100 percent in selected environments and tripled the capacity of the 3390 Direct Access Devices by adding a new member to the storage hierarchy.
IBM announces scientific results that may allow a 30-fold increase in the amount of data stored in a given area of magnetic disk surface within the next decade.
Yes, like a giant demonic Seeburg. The actuators were hydraulic, and put considerable dynamic loads on the computer flooring. You could feel the bumps through your feet anywhere nearby.