In January, 1986, Apple introduced the Macintosh Plus and a double-sided 800K capacity disk drive, which used the new HFS disk format providing directories and sub-directories. A revised external drive case was produced to accommodate the slimmer 800K disk mechanism. The Macintosh 800K External Drive (M0131) could only be used with Macintosh models except the original 128K, which could not load the new HFS file format required for use with the drive. However, the new drive did support the older 400K single-sided disks allowing them to be shared. Like the 400K drive before it, Apple’s GCR formatting allowed for variable speed to accommodate a higher storage capacity than its 720K PC counterparts. In addition, the new Sony mechanism was much quieter and significantly faster than its predecessor. Designed primarily to run on Macs with the new 128K ROM which contained the necessary code to support the drive, it could be used with the older 64K ROMs if the proper software was loaded into the Mac’s RAM via the HD20 INIT installed into the system folder. The drive itself controlled its own speed internally and was no longer dependent on an external signal from the Mac, which was blocked on the early drive mechanisms compatible only with the Macintosh. Later universal mechanisms, first used on the Apple II to accommodate proprietary signals, required special cables to isolate the speed signal from the Mac, to prevent damage to the drive. However, with the increased storage capacity combined with 2-4x the available RAM on the Mac Plus, the external drive was less of a necessity than it had been with its predecessors. Nevertheless, with the only option for adding additional storage being extremely expensive hard drives, Apple increased the ability of the Macintosh SE introduced a year later, to access up to 3 floppy drives simultaneously (only one of two Macs to do so).