of error correction, which makes the drives more reliable and reduced costs because small imperfections in the disk surface can be tolerated. The circuitry can correct error bursts up to 11 bits long through use of fire codes. The 1973 3330 Model 11 features IBM 3336-11 Disk Packs that held up to 200 MB (808x19x13,030 bytes). IBM 3333 The 3333-1 and the 3333-11 contain two 3330 type drives and a controller that attach to a director type storage control. Up to three additional 3330 type DASD (six drives) can then be attached to a 3333. The 3330 was withdrawn in 1983. IBM 3340 and 3344 The IBM 3340 and 3344 have similar characteristics. However, only a 3340 can serve as head of string; there are no A model 3344 drives, and a 3344 must be attached to a 3340 A model as head of string. IBM 3340 The IBM 3340 Direct Access Storage Facility, code-named Winchester, was introduced in March 1973 for use with IBM System/370. Three models were announced, the 3340-A2 with two drives and a controller, the models B2 (two drives) and B1 (one drive). B-units can connect to the model A2 to a maximum of eight drives. It uses removable data modules that included the head and arm assembly; an access door of the data module opens or closes during a mechanical load/unload process to connect the data module to the drive; unlike previous disk packs and cartridges there is no cover to remove during the insertion process. Access time is 25 millisecond and data transfers at 885 kB/s. Three versions of the removable IBM 3348 Data Module were sold, one with 35 megabyte capacity, another with 70 megabytes, the third also has 70 megabytes, of which 500 kilobytes were accessible with fixed heads for faster access. The 3340 also uses error correction. It was withdrawn in 1984. The 3340 was developed in San Jose under the leadership of Ken Haughton. Early on the design was focused on two removable 30 megabyte modules. Because of this 30/30 configuration, the code name Winchester was selected after the famous Winchester .30-30 rifle; subsequently the capacities were increased, but the code name stuck. One significant aspect of this product, and the reason that disk drives in general became known as "Winchester technology", was that this head design was very low cost and did not require the heads to be unloaded