Beyond the 1541 - Mass Storage for the 64 and 128 - from Compute!, February 1986

Beyond the 1541
Mass Storage For The 64 And 128
Selby Bateman, Features Editor

A 3.5-inch microdisk drive for the 64? A hard disk storage system for the 128? The continuing evolution of personal computers is causing major shifts in the kinds of data storage devices being used. There are signs that even the familiar 5-1/4-inch floppy disk may eventually go the way of punch cards and paper tape storage methods. Here's a look at what's headed your way in the emerging microcomputer industry Commodore market.

Consider the 1541 disk drive: It's been called a "toy," a "lumbering hippo," and "the albatross of the Commodore 64." Business users impatiently deride its slow operating speed. Alternative devices and software speedup schemes have been offered by other manufacturers. And even defenders of the 1541 have been known to drum their fingers waiting for it to load data at a relatively slow 512 bytes per second.

Yet despite the insults hurled at the 1541, one Commodore source estimates that as many as three-quarters of the five million 64s and VIC-20s sold worldwide are used with 1541s (or the earlier 1540 drives). The slow but relatively inexpensive 1541 became another salvo in the continuing battle to bring down prices and spur consumer sales of computers.

It's difficult to believe that the 64 and the 1541 are almost four years old. At the Consumer Electronics Show (CES) in January 1982, Commodore introduced its new 64K computer at a suggested retail of $595, a breakthrough in price and power. Commodore also introduced a companion for the 64: the 1541 drive, a direct descendant of earlier drives used with the VIC-20 and PET computers.

When first released, the 1541 sold for almost $600. But prices dropped swiftly, just as they did for the 64 itself. Soon, a 1541 could be bought for $399, then $299, and $250. Today, a new 1541 can be purchased from some vendors for as little as $149, and used 1541s frequently are available for $99.

But for many 64 users, the 1541 was not their first storage device. Commodore's Datassette tape recorder, a digital cousin of the common audio cassette tape recorder, was offered at even less expense.

Why tape recorders? The emerging microcomputer industry borrowed ideas from mainframe computer systems, and tape storage proved to be a natural - inexpensive and dependable. The problem with tape storage is its speed.

A tape recorder is a sequential access device. That is, the magnetic information is read sequentially from the tape as it passes in front of a stationary read/write head. To get to a particular program on the tape, several other programs may have to slide by the tape head before it reaches the one you want.

On the other hand, a disk drive is a random access device. The read/write head moves across a spinning disk, much like the stylus of a record player moves across the face of an album. The result is a much more efficient means of data access than a cassette tape. Although the 1541 is slower than other computers' disk drives, it is much faster than a Datassette.

Despite its slowness, the Datassette and some third-party cassette recorders introduced thousands of computer users to data storage in the early years of the Commodore 64 and the VIC-20. Commercial software was usually offered in both tape and disk format (and frequently in plug-in ROM cartridges). But during the past year and a half, virtually all commercial software vendors have forsaken tape versions of 64 software. The thousands of commercial programs available for the 64 are almost all on disk. And at Commodore, stacks of Datassettes sit boxed and ready with no place to go. Technology has rendered them obsolete.

A computer as inexpensive as the 64 had to have a disk drive in the same price range. To cut costs, Commodore equipped the VIC and 64 drives with serial data transmission ports, much slower than the IEEE parallel ports used in the earlier PET disk drives. Adding to the problem, Commodore engineers reportedly had to slow very slightly the original data transfer speed of the 1540 (designed for the VIC) in order to make the new 1541 drive compatible with the 64 - an engineering concession to marketing plans for the computers.

A serial connection moves only one bit of data at a time, rather than multiple bits sent simultaneously in a parallel connection. Further slowing serial transfer between the 64 and the 1541 is the fact that the VIC and 64 (and Plus/4 and 16) require the computer's main microprocessor to disassemble a byte of information into its individual bits, add several controlling bits, and then send the information. This takes extra time for the microprocessor. A special-purpose hardware serial device could accomplish this much faster.

That's exactly what Commodore has done in the new 128 computer and its 1571 disk drive. Special hardware takes care of most communication handling (the first CIA chip takes on extra work), freeing the microprocessor from these chores and thus increasing the speed of transfer. Commodore calls this serial fast mode as opposed to the 64/1541 slow mode. As 1571 owners know, their disk drives can actually work at different speeds, depending on whether it's in 1571 mode for the 128, 1541 mode for the 64 or 128, or