One exception was the TI-99 series, announced in 1979 with a 16-bit TMS9900 CPU. The TI was originally to use the 8-bit 9985 processor designed especially for it, but this project was cancelled. However, the glue logic needed to retrofit the 16-bit CPU to an 8-bit 9985 system negated the advantages of the more powerful CPU. Another exception was the Soviet Elektronika BK series of 1984, which used the fully 16-bit and powerful for the time 1801 series CPU, offering a full PDP-11 compatibility and a fully functional Q-Bus slot, though at the cost of very anemic RAM and graphics. The Motorola 6809 was used by the Radio Shack TRS-80 Color Computer, the Fujitsu FM-7, and Dragon 32/64. Processor clock rates were typically 1–2 MHz for 6502 and 6809 based CPU's and 2–4 MHz for Z80 based systems (yielding roughly equal performance), but this aspect was not emphasized by users or manufacturers, as the systems' limited RAM capacity, graphics abilities and storage options had a more perceivable effect on performance than CPU speed. For low-price computers the cost of RAM memory chips contributed greatly to the final product price to the consumer, and fast CPUs demanded expensive, fast memory. So designers kept clock rates only adequate; in some cases like the Atari and Commodore 8-bit machines, coprocessors were added to speed processing of graphics and audio data. For these computers clock rate was considered a technical detail of interest only to users needing accurate timing for their own programs. To economize on component cost, often the same crystal used to produce color television compatible signals was also divided down and used for the processor clock. This meant processors rarely operated at their full rated speed, and had the side-effect that European and North American versions of the same home computer operated at slightly different speeds and different video resolution due to different television standards. Initially, many home computers used the then-ubiquitous compact audio cassette as a storage mechanism. A rough analogy to how this worked would be to place a recorder on the phone line as a file was uploaded by modem to "save" it, and playing the recording back through the modem to "load". Most cassette implementations were notoriously slow and unreliable, but 8" drives were too bulky for home use, and early 5.25" form factor drives were priced for business use, out of reach of most home buyers. An innovative alternative was the Exatron Stringy Floppy, a continuous loop tape drive which was much faster than a datacassette drive and could perform much like a floppy disk drive.