Review of:
Backer 
by Robert Fuller, Alamo PC

 Backer comes either as an internal ISA card ($69) or an external printer port version ($79). You can order it online from www.harkmarketing.com or mail order from Hark Marketing Inc., 531 North 150 West, Kaysville, Utah 84037 or Jameco Electronics, 1355 Shoreway Road, Belmont, CA 94002-4100. I have the internal unit, but the external unit is much more versatile as you can easily move it from computer to computer. VCR's are not designed for digital data. 

 A VCR is designed for recording a wide band video signal. Video tape manufactures are interested in getting the widest frequency response possible from their tapes for the best picture. They are not too concerned about small imperfections in the tapes that cause the video signal to drop out. Dropouts, seen as small white or black streaks on the picture, are noticeable only if you're looking for them or they become excessive due to a crease in the tape or other malfunction. A dropout can lose digital data. The longer the dropout, the greater the data loss. 

To combat these dropouts a data encoding technique is used to enable the computer to rebuild the lost data. Data tapes are expensive because they are certified to be error free. The tapes are recorded and read back to be sure that they are good. That extra checking increases cost. Tape certification is impractical with VHS tapes. The helical scan used by the video heads causes them to record in a different path each time the tape is recorded. Recording and checking the tape would only give you a general idea of how good the tape was. 

A test reported in "Popular Electronics" (Nov., 1992, pg. 32) measured dropouts per minute for several brands of tape. The name brand tapes averaged 14 dropouts per minute while some imports averaged 800 to over 990 dropouts per minute. Jeremy Carter from KODAK E-mailed this about the KODAK HG tape; "The dropout values for the past year are actually averaging less than 4 dropouts per minute (15 uSec, 20db) with a standard deviation less than 6." 

I have eight pages of notes from my testing with two different VCR's and four tapes. The best two tapes were KODAK HG and POLAROID HG. I was able to record 300 MB of data with only 6 uncorrectable errors on the KODAK HG tape in the VCR Long Play speed. The JVC PRO and JVC EHG both had excessive data signal dropouts even though they were more expensive For a given bad spot on the VCR tape, the data loss is less with the highest tape speed and you'll get the best results at the Standard Play speed. 

A raw data rate of 2 MB per minutes means that a 2 hour tape will hold about 240 MB of uncompressed data. My Colorado 250 will hold about 120 MB of uncompressed data on a $15 tape and take an hour to record. You do have to check or verify the Backer tapes to make sure that you find and replace any bad files. You can make duplicate copies of your files, but it takes twice as long to do. 

 Backer uses white and black pulses to record digital data. The bottom of your TV screen shows the tape header information and then the record or file number in block characters so that you can see where you are on the tape. Backer offers a "LO" (2MB/Min) and a "HI" (4MB/Min) speed mode. The "LO" mode pulses are twice the length of the "HI" mode pulses. A long signal dropout on the tape can cause data loss. 

 Backer uses a Reed Solomon encoding method to recover lost data. Data recovery takes a lot of CPU time. The time varies with the amount of data dropped and the format you have set up Backer to use. Unfortunately the VCR tape is still moving and inputting more data to be processed at the same time you are doing the data recovery. The new data might also require correction and the recovery time builds up. 

 My 486-80 CPU falls behind in "HI" speed mode. When it falls too far behind it cannot take anymore input data and the data is skipped. This results in lost data and files that are not recovered from the VCR tape. Backer relies on software buffers instead of hardware buffers to keep the cost down. The world of Windows is not a real time world. When your computer runs out of memory in Windows, it uses the swapfile on your hard drive as extra memory. Anyone with a Pentium and a fast disk drive should be able to use the "HI" mode, but until I get a CPU upgrade I'm stuck with the "LO" mode. 

 If you have any long files such as any 10 MB video files, use WinRar to split them up into 500 KB segments so that a tape error will not make the whole file unusable. I don't like to use zipped files when evaluating anything as the compression figures vary with file types and are not consistent. If you are backing up text or program files, you may be able to use the built in zip compression to double your throughput rates and the capacity of your tapes. In theory, if you used the VCR extended play mode with zipped files and the "HI" mode, you could store up to 3,240 MB on a 6 hour tape. 

 I have the original version of Backer. It is hardwired to use the Direct Memory Access (DMA) port 1, the same port used by most sound cards. If your sound card uses DMA 1, you will have to change it or use the lockout feature of the Backer software to keep the sound card from interfering with Backer. The newer versions of Backer can be jumpered for DMA 1 or 3. The address locations used by the card are selected by jumpers. 

 The Backer software is 16 bit for Windows 3.1 and 32 bit for Win95. It is straightforward and should not present any problems You will not be able to use the Seagate Direct Tape Access program with Backer, but you can fast forward to any file number using the TV screen display. You can restore individual files that way. A good feature is that you can make an emergency floppy disk to load Backer from if you cannot access your hard drive or Windows. 

 Except for being stuck in the "LO" mode, I like Backer. I plan to buy the external version so that I can free up an ISA slot for something else to use. I do hope that the next generation will include some hardware buffering and use the VCR color capabilities to make the units faster. 

 Bob Fuller, W6TVJ (Extra Class), is the technical system operator on the Alamo PC BBS.