IBM 2321 Data Cell
A direct access storage device using magnetic tape strips.
The IBM 2321 Data Cell was a direct access storage device for the System/360, first shown when that computer line was introduced in April 1964. It could store up to 400 megabytes, and retrieving data took between 95 and 600 milliseconds, depending on where the strip was located and how data was arranged inside the cell. The storage medium was short strips of magnetic tape, which earned the machine the nickname "noodle picker" because the strips looked like pasta. IBM stopped selling the 2321 in January 1975.
The drive held up to ten removable data cells, each with a capacity of 40 megabytes. Inside each cell were 200 tape strips, each 2.25 inches wide and 13 inches long. Total storage came to 400 megabytes, or 800 million decimal digits. Up to eight 2321 units could connect to a single IBM 2841 Control Unit, giving a combined capacity of over three gigabytes.
Compared to the contemporary IBM 2311 disk drive, the 2321 held 55 times more data but was about seven times slower (85 ms versus 600 ms access times). A fully loaded 2841 Control Unit with eight 2321 drives had the same capacity as 441 IBM 2311 disk drives, which would have required 56 control units and seven data channels.
The Data Cell used three separate seeking systems that worked at the same time: a servo-hydraulic mechanism rotated bins to pick the correct subcell, and two solenoid-driven systems—one selected the right strip tab from the ten in a subcell, and the other chose one of five head positions for the 20-element read/write head (giving 100 tracks per strip). The hydraulic fluid was Mobil DTE Light, a machine tool oil pressurized to 1500 psi. Despite stories about oil leaks, they were rare. The oil reservoir held 5 US gallons.
Even though it used magnetic tape, the 2321 was classified as a direct access storage device because it could go straight to a record without scanning the whole tape. The System/360 channels treated it like a disk drive, using a six-byte seek address in the form ØBBSCH (hexadecimal), where the first byte was zero and the remaining bytes specified the bin (cell and subcell), strip, cylinder, and head.
- Announced
- April 1964
- Withdrawn
- January 1975
- Capacity
- 400 megabytes (800 million decimal digits)
- Access time
- 95 ms to 600 ms
- Storage medium
- magnetic tape strips (2.25 in × 13 in)
- Max units per controller
- 8
- Max capacity per controller
- over 3 GB
Lore & Background
The 2321 houses up to ten removable and interchangeable data cells, each containing 40 megabytes. Each data cell contains 200 strips of magnetic tape, which are the basic recording media. Strips are 2+1/4 in wide and 13 in long. The total storage capacity is 400 megabytes or 800 million decimal digits. Up to eight 2321s can be attached to the IBM 2841 Control Unit, allowing an overall capacity of over three GB.
In comparison to the contemporary IBM 2311 Disk Device, the IBM 2321 Data Cell Device holds 55 times more data, while being only seven times slower (85ms and 600ms access times respectively). One fully loaded IBM 2841 Control Unit connected with eight IBM 2321 Data Cell Devices has the capacity of 441 IBM 2311 Disk Devices, which would need to be connected to 56 IBM 2841 Control Units, which would require seven data channels.
The Data Cell makes use of three concurrently operating separate seeking systems: a servo-hydraulic one to rotate the bins to select the proper subcell, and two solenoid driven ones: one to select the correct strip tab of the ten in the subcell, and the other to select one of the five head positions, for the 20 element head (100 tracks per strip). The hydraulic fluid, Mobil DTE Light, a machine tool circulating oil, is pressurized at 1500 psi and despite a lot of folklore about oil leaks, they were very rare. The oil sump holds 5 USgal.
Reader's Guide
Although its storage medium is tape, the 2321 is classified as a direct access storage device which can directly access a record rather than scan all the tape to find a record as would a conventional tape drive. IBM's System/360 channels addressed the 2321 as a direct access storage devices, i.e., a disk drive, with a 6-byte seek address of the form ØBBSCH (hexadecimal) where the first byte is zero and the remaining bytes address the Bin (i.e., cell and sub-cell), Strip, Cylinder and Head. This addressing scheme allowed the device to be integrated into the same channel architecture as disk drives, despite its tape-based media. The 2321's capacity advantage over contemporary disk drives was substantial—one fully loaded controller with eight units could replace over 440 disk drives—but its slower access time and mechanical complexity limited its adoption. The device was withdrawn from marketing in January 1975, reflecting the rapid advancement of disk storage technology that soon made its capacity advantage less compelling.
Did You Know?
- The IBM 2321 Data Cell was nicknamed 'noodle picker' because its magnetic tape strips resembled pasta noodles.
- The hydraulic fluid used in the 2321 was Mobil DTE Light, a machine tool circulating oil, pressurized at 1500 psi.
- One fully loaded IBM 2841 Control Unit with eight 2321s had the capacity of 441 IBM 2311 Disk Devices.
- The 2321's seek address format was ØBBSCH (hexadecimal), addressing Bin, Strip, Cylinder, and Head.
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