The Evolution of the Disk Drive

by Joel Ellis Rea

First there was the Commodore 2001 Personal Electronic Transactor (PET).  It was one of the first
personal computers on the market.  It had a whopping 4K of RAM, and 8K BASIC in ROM, and a
Kernal to control input/output and other system operations.  It used Commodore BASIC Version 1. 
There were no disk drives then, but provisions were made in the form of an IEEE-488 General
Purpose Interface Bus.  It also had the funniest little keyboard you ever saw!

Commodore then invented the 2040 Dual Floppy Disk Drive.  It was an industry first.  Previously the
main computer had to control every tiny detail of disk drive operation, not to mention loading a large
Disk Operating System (DOS) into the computer's RAM in order to use the drive.  The 2040 was an
intelligent drive, with its own computer system inside, and its own DOS in ROM!  By simply PRINTing
commands to its command channel, BASIC users could SCRATCH, RENAME, and COPY files, and
DUPLICATE an entire disk without any further help from the computer.  Only problem was, they
could not SAVE or LOAD programs, or use data files.

The problem was BASIC V1.  It did not know about the timing involved with actually transferring data
back and forth between the computer's RAM and the disk drive's computer.  So, Commodore created
Upgrade BASIC (now known as BASIC V2), and put it into a new PET, called the 2008.  It had 8K
of RAM, a REAL keyboard (unlike other companies, Commodore NEVER tried a rinky-dink
keyboard again!), and it could use the disk drive!

But the 2040 drive had its faults as well.  It could not handle random access files (one of the most
important advantages of a disk drive over a tape drive) without a LOT of effort on the user's part.  It
could not trap errors correctly, and it required the user to type OPEN 15,8,5,"I":CLOSE 15 every time
a disk was changed.  It could not seem to center the disks properly.

So about the time Commodore came out with their 3008 PET computer (including BASIC V3, with
very minor differences from V2), they introduced the 3040 Dual Disk Drive.  This had DOS V1.2 in it,
which corrected the error trapping problems.  But they did not fix much else.  Also, people were getting
tired of having to type OPEN 15,8,15 etc. when their Apple-owning buddies could do the same with
RENAME oldfilename, newfilename.

Almost immediately thereafter, the Commodore 4016 PET came out. It had 16K, expandable to 32K,
and BASIC V4. This version had nice disk commands like CATALOG, SCRATCH, DLOAD,
DSAVE, BACKUP, COPY, etc.  These commands simply translated themselves into the old
commands that the drive could understand.  

Along with the PET 4016 came the 4040 disk drive.  It had it all!  Besides fixing the hardware
problems, it had DOS V2.1, which supported relative files (also referred to as random files).  The new
DOS also performed an automatic "I" (initialization) every time it detected a disk with a different ID, so
the user did not have to type this command unless he had two or more disks with the same ID.  It also
used a slightly different disk format from the 2040's and 3040's, so that a disk made on a 2040 could
be used only by copying its files to a 4040 drive. 

Later, Commodore came out with the CBM 8032.  It had BASIC V4, 32K of RAM, a 12-inch
80-column monitor (the old machines had 40 column screens), and a more business-like keyboard. 
Indeed, it was a business machine.

A business machine needs a business disk drive.  So Commodore presented the 8050 disk drive.  It
used a double density format that allowed over twice as much data on each disk.  It also could tell if a
disk drive door had been opened, and automatically did an "I" command when the door was shut again.

Later came the 8052 double-sided drive, and the D9060 and D9090 hard disk units that could store 2,
5, and 7.5 megabytes (1 meg=1024K).

Then came the VIC20.  Commodore made many advances on this one.  Low price!  Graphics!  Low
price!  Color!  Low price!  Three-channel sound, RS232, eight user-programmable function keys, and
a game cartridge slot.  Not to mention low price!  Even though they were producing a computer to
compete with home video games, they learned their lesson with the PET 2001 and gave the VIC 20 a
REAL keyboard.

But for the sake of low price, Commodore took several MAJOR steps backwards.  Only 5K of RAM,
22-column screen, back to BASIC V2.  And worst of all, they scrapped the wonderful IEEE-488 bus
that could shove all eight bits of a byte down the wires at once, and replaced it with a "serial bus" that
had to spool those bits out one at a time.

Commodore then produced the 1540 Single Floppy Disk Drive.  It was basically a one drive, serial bus
version of the 4040.  It had less RAM, so that fewer files could be open at any one time.  It used the
new half-high disk drive units.  Instead of two microprocessors (one for the drives and one for the
interface), it had one processor controlling the single drive and the interface.

About two years later Commodore invented the Commodore 64!  (Ever hear of that one?)  I will not
go into all of its nice features, but it still had the serial bus and BASIC V2.  Along with it of course
came old slow and poky, the much hated, much loved 1541 that so many of us use and cuss daily.

 (from George's Den BBS via Greater Oklahoma Commodore Club Newsletter, 6/88, via The
Commodore Information Center web site (http://home.att.net/~rmestel/commodore.html) )