If they think of Peter Norton at all, most owners of personal computers probably think of him as "the disk man," or perhaps as the finder of lost files. This is not completely fair; Norton has spread enlightenment on other aspects of computing hardware and programming. But only a small fraction of those who use a PC every day ever feel a need for his "Programmer's Guide" or his "Assembly Language Book" -- though, should such a need arise, they might be inclined to turn first to Norton.

Norton's name is also familiar from his regular and highly readable column in one of the major PC magazines. But he stands out in the minds of PC users as the deviser of "The Norton Utilities," now available in an "Advanced Edition" of its "Version 4.0." Utilities are specialized programs, usually rather small and limited in scope, that are designed to enhance the functioning of computer hardware. Peter Norton's utilities have probably done more than any other resource available to make the average PC user familiar with the inner workings of those mysterious disks that store and regurgitate the results of our hours at the keyboard.

In the beginning, the Norton utilities allowed us to examine only floppy disks in clinical detail, but the latest editions also make it possible to track down lost files or directories, to map and reorganize space allocations, to display directory trees and search for text, even (amazingly) to reverse the consequences of untimely formatting on hard disks as well. But, floppy or hard, the most spectacularly useful function of the Norton Utilities is the recovery of erased disk files.

Sooner or later, it happens to anyone who works with a computer. The wrong button gets accidentally pushed and a file, perhaps containing months or years of work -- irreplaceable material -- is erased. Before Norton came along, that was grounds for despair. And in earlier editions of the utilities, recovery of erased files was an iffy and a difficult process. Now, with Norton's QU (for Quick UnErase utility), recovering erased material seems hardly more difficult than calling up a regular file.

The secret lies in the essential laziness designed into computers. In the interests of efficiency, they are programmed not to do any more work than is necessary for a given purpose. When it comes to "erasing" a file, what this means is that the computer actually erases only the first letter of the filename, substituting a question mark. In Washington, this fact might induce acute paranoia, and Norton has worked out a solution for that, too, but we will look at that later.

Erasure (the substitution of a question mark for one letter) removes the filename from the standard directories set up by DOS (the disk operating system). It also serves as a sort of beacon, telling DOS that the space is no longer reserved for that file but is available for storage of new material. Until such material is stored, however, the file remains intact except for the first letter of its filename. It will even be copied to another disk if you use the "DISKCOPY" command, which produces an exact duplicate, rather than copy individual files, one by one, through the directory.

In some cases, you may erase a file deliberately and not realize until months later that there was something in it that you want to see again. If that space on the disk has not yet been overwritten, the "erased" file should still be there, ready for recovery, no matter how much time has passed. The QU utility will bring up on your screen a menu of erased files, each beginning with a question mark, and all you have to do to restore that file is overwrite the question mark with the first letter (or number) of the original name.

If part of the erased file has been overwritten, the job of recovery becomes much more complex and difficult, but not necessarily impossible. For this assignment, you leave QU aside and go to the more powerful UnErase function in the Norton Utilities main program (called NU, short for Norton Utilities). Using this program can have some of the excitement of putting together a jigsaw puzzle, particularly if the file you are trying to recover was a long one, assembled at various times and occupying noncontiguous spaces on your disk. UnErase will track down various detached (theoretically erased) segments of text scattered across the disk, bring them up to the screen for you to examine, and allow you to piece them back together in proper order or even copy them to another disk.

You are much less likely to reformat a hard disk accidentally, at least in the normal day-to-day operating of a personal computer, but it can happen and has happened. Reformatting is supposed to "erase" all the information previously stored on the disk, but (as in the case of "erased" files) this turns out to be not quite (or not always) true. It is essential, however, that if you are to uncover a reformatted disk you do so before new files are stored on it. The FR (Format Recover) function (which works only with hard disks) also requires preventive care, saving essential information to a file called FRECOVER.DAT, but this can be made an automatic function (part of signing on, for example) and Norton's manual tells you how.

After such an emphatic demonstration that "erased" material may not really be erased, Norton has also provided a couple of utilities that will unequivocally wipe out material stored on a disk. Appropriately named "WIPEDISK" and "WIPEFILE," these are described as "maximum security" systems and each has a special mode that "follows certain Government rules for security wiping." It also has a mode that "deletes files but does not wipe them," and another that will overwrite the file repeatedly -- dare we say obsessively? You can pick the number of times the file gets overwritten with a string of zeros or similarly enigmatic material. If you want to be really sure, you can have a file overwritten up to 256 times, though the Department of Defense finds that three is usually sufficient.

These are only a small part of what is available in "The Norton Utilities 4.0 and Advanced Edition." There is "ASK," for example, which can be used to make your batch files interactive. With this utility, the computer will stop in the middle of executing a series of programmed commands to ask you for new instructions.

"FILE FIND" will search through every drive and directory in your system to find a filename whose location you have forgotten. SI (or "System Information") will investigate your system and give you a report on its status and capabilities.

"DISK MAP" does what its name suggests: shows you the contents of your disks (even, in this edition, a hard disk) in the format of a map rather than the usual lists and directories. The map will also display individual files, with written information about their size, location and type (e.g., program or archive), or the program can be asked for technical information on the disk drive, its capacity, free space, systems of organization, size of sectors and directories, etc.

A supplement to these programs, not part of the excellent manual but rather a long-range view that puts many of the utilities in perspective, is "The Norton Disk Companion," a 36-page pamphlet that is included in the utilities package and is designed to tell the average nonspecialist everything he might want to know about disks.

The Norton Utilities Version 4.0 & Advanced Edition. For IBM PC and compatible systems. $150 from Peter Norton Computing, Inc. 2210 Wilshire Boulevard #186, Santa Monica, Calif. 90403. (213) 453-2361.

Tuned in

Your computer plays chess with you, balances your checkbook, faithfully stores the text of your memoirs and the telephone numbers of all your friends and business associates. But are you happy? Of course, not. For years, you've been wanting to teach your computer how to whistle "Yankee Doodle" or hum "We Won't Be Home Until Morning."

Well, you need suffer no longer. With PC Musician, a program devised by Christopher Wiley of Prescott, Ariz., you can have your IBM or compatible computer chirping "Caro nome" or "Streets of Laredo" in less time than it takes to tune your piano. It is a note-processing program -- fairly similar to word-processing systems -- except that its output is tones on the computer's loudspeaker rather than words on a screen or printer.

A computer is not an orchestra or a string quartet; it produces only one note at a time, and no program could make it play harmony or counterpoint. But PC Musician will allow you to input, store and play back any melody you are able to type out in standard notation on a regular five-line staff. Perhaps your computer won't greet you at the door with your slippers and a cold martini, but once you get this program working, it will hum "Melancholy Baby" when you ask it to.

"PC Musician" is freeware, which means that copying and free distribution is encouraged by the inventor. If none of your friends have it, you can get a copy by sending a blank, formatted disk with an addressed, postage-paid return mailer to: Christopher Wiley, Box 111, VAMC, Prescott, Ariz. 86313. Wiley will send you the program with a polite suggestion that, if you like it, you send him a contribution ($20 suggested).

Poster Perfect Another piece of freeware, Bannerific by Alan C. Elliott, can transform your PC and printer into a banner-making press. The program makes banner-size letters by clustering regular type into larger, alphabet-formatted blocks. The banner text will run sideways along the continuous sheets of paper that come out of your printer.

Get all your systems going together, and you can have the computer chiming "Happy Birthday to You" while the poster says it graphically. Write Mission Technologies, 1028 North Madison Ave., Dallas 75208. Elliott would appreciate support but does not suggest how much.

Either or both of these programs (along with hundreds of other freeware items) can be ordered from Shareware Express, 31877 Del Obispo, Suite 102, San Juan Capistrano, Calif. 92675 for $5.95 each plus postage and handling costs.