capacity is stated as 112 MB. The 2302 attaches to IBM mainframes via a IBM 2841 Storage Control Unit. IBM 2305 The IBM 2305 fixed head storage (a fixed-head disk drive sometimes incorrectly called a drum) and associated IBM 2835 Storage Control were announced in 1970, initially to connect to the 360/85 and 360/195 using the IBM 2880 Block Multiplexor Channel. The 2305 Drive was in much demand when the System 370 offered Virtual Storage, and these 2305s were often used for paging devices. They were used in this way on 3155, 3165, 3158, 3168, 3033, 4341, and 3081 (with special feature microcode.) The 2305 was also used for high activity small data sets such as catalogs and job queues. The 2305-1 runs at 3.0 MB/second when attached using the 2-byte channel interface, and the larger 2305-2 runs at 1.5 MB/second. The 2305 provides large-scale IBM computers with fast, continuous access to small-sized quantities of information. Its capacity and high data rate make it ideal for some systems residence functions, work files, job queues, indices and data sets that are used repeatedly. Its fast response time makes it attractive as a paging device in a heavily loaded systems, where there are 1.5 or more transactions per second. IBM 2311 The IBM 2311 Disk Storage Drive was introduced with the 2841 Control Unit in 1964 for use throughout the IBM System/360; the combination was also available on the IBM 1130 and the IBM 1800. The drive also directly attaches to the IBM System/360 Model 20 and the IBM System/360 Model 25. All drives used the IBM 1316 Disk Pack introduced with the IBM 1311. The 2311 Model 1 attaches to most IBM mainframes through a 2841 Control Unit; it attaches to the System/360 Model 25 thru a Disk Attachment Control which provides the function of the control unit. Disk packs are written in these attachments in IBM's count key data variable record length format. The 2311 models 11 or 12 are used when attached to an integrated control of the System/360 Model 20 and the disk packs are written with a fixed sector format. The disk packs are not interchangeable between those written on the Model 1 and those written on the Models 11 or 12. The 2311 mechanism is largely identical to the 1311, but recording improvements allow higher data density. The 2311 stores 7.25 megabytes on a single removable