Product: AERCO FD-ZX Floppy Disk
Machines: ZX/TS
Price: Interface $179.00
Disk Drive $189.00
Cable & PS $79.00+$4 P&H
From: AERCO
POB 18093
Austin, TX 78760
512/331-0719
If you value your time and would like to eliminate waiting 6 minutes for a program to LOAD, a floppy disk drive may answer your needs. AERCO‘s FD-ZX, while not inexpensive, satisfies my needs for fast mass storage.
Floppy diskettes come in various sizes. They are thin mylar disks impregnated with iron oxide, just like the recording medium on cassette tapes. Magnetic heads in the disk drive record and play back data, like cassette players. But in a floppy disk drive, the diskette rotates at a constant 300 RPM and the recording head can position itself (under computer control) to many different tracks on the diskette. Each track is circular and concentric with all the other tracks. An entire diskette can be searched for a program in a few seconds.
AERCO’s disk system consists of three major components:
1. Interface board. This professionally designed circuit board contains a 2716 EPROM chip containing the disk operating system, a 1797-02 floppy disk controller IC, and a number of smaller interfacing chips. It mounts on a special ribbon connector to the expansion bus of the ZX/TS. It provides a 34 pin edge-card connector for connecting the disk drive(s). Up to 4 drives may be run from this board.
2. Disk drive. I purchased a Pertec FD-250 drive, which handles 35 tracks per side. It can store almost 1/4 megabyte per side. Pertec no longer manufactures disk drives, so you may want to get a different brand.
3. Power supply. Supplies 12V at 2 Amps and 5V at 1 Amp. AERCO supplies cables for the drive with the power supply. You could make up your own cable from parts if you already have a power supply to use.
AERCO provides a somewhat sketchy 10 page operating manual, but it suffices to get you up and running. After a brief discussion of disk theory it presents a step-by-step installation procedure. It says how to power up, insert the DOS disk and execute a USR call to bring the system up. In a scant 2 seconds you’ll get AERCO’s 16K or 64K DOS Menu.
This will allow you to format blank disks (you have to do this before storing programs or data on them), LOAD one of sixteen 16K programs into memory, rename programs on disk, copy disk to disk (if you have two drives), and a few miscellaneous utilities. To SAVE a program, you must break the program (or add an extra line) and execute a USR call to the “page” on which you want to SAVE the program. I leave DOS on page 1 of all my disks and store 15 other programs on the disk. Any of these can be called from DOS by selecting the page number from sub menu, or they may be LOADed directly with a USR call.
You can save up to six 64K programs on one disk, select single or double density recording (single more reliable; double more data). In some cases, the buffer used for double density recording (which is twice as long as the buffer for single density) may intrude into the variables area of your program.
Despite its advantages, the AERCO system has some disadvantages you should know about. You must use USR calls to store and retrieve programs. SAVE and LOAD would have been easier to work with. It’s too easy to use the wrong USR routine and write over the disk when you meant to read.
Addresses of some of the EPROM disk routines appear in the documentation, but not elaborated upon enough for the average user. The section on 64K programs seemed to indicate that they can be written to disk, but only 16K might be retrieved. AERCO says up to 52K will be retrieved, all the way up to E_LINE.
You can only store 16 programs (up to 16K each) on a disk, regardless of program length. Even a 1K program takes up 16K disk space.
This unit is an excellent value for those of us committed to our ZX systems. It’s fast, reliable, and reasonably easy to use. Better documentation and a more versatile operating system would have been a plus, but even as is, the FD-ZX fits the bill. [Editors Note: AERCO no longer offers the Pertec drive, and instead now sells an equivalent Panasonic drive for $210 + $6 P&H.]