Chapter 7
1972- 1977
The Personal
Computer
1
Paul Ceruzzi
“The development of personal
computing followed a
trajectory that is difficult to
explain as rational.”
2
Mark Twain
“Very
few things happen at
the right time, and the rest
do not happen at all. The
conscientious historian will
correct these defects”
3
Stewart Brand- Stanford
“Ready or not, computers
are coming to the people.
That’s good news, maybe
the best since psychedelics.”
Rolling Stone Magazine
December 7, 1972
“Spacewar: Fanatic Life &
Symbolic Death Among
Computer Bums”
4
TOPS-10 & PDP-10
• PDP-10  large
mainframe
– Spacewar & Timesharing @ Stanford
– Good operating
system + disk
• 1972  TOPS (@ MIT)
– Timesharing
operating system
– Description Pg. 209
– Sounds like… DOS
• Though mainframe,
“it was personal”
First PDP-10
5
TOPS-10 (cont.)
• PIP - Peripheral Interchange System
–Moved files to and from I/O devices
• TECO - Text editor & corrector
–Text editing from a terminal
• DDT - Dynamic Debugging Tool
–From terminal
• Simple and elegant: user “in control”
6
Early Time Sharing
• Scientific Data Systems (SDS)
– SDS-940 – did well in market
But timesharing did not
– Berkeley, ARPA
become personal
enough! $$$
– Bought by Xerox
• Xerox PARC
– MAXC-Multiple Access Xerox Computer
• A PDP-10 clone
• Tymshare, CA
– One of the few companies that leased time
and survived
7
– Bought by McDonnell- Douglas
Personal Computing
• Chuck House, Hewlett Packard
RE: Calculators
“One could charitably say we
invented nothing: we simply
took all the ideas that were out
there and figured out how to
implement them cost
effectively”
8
Personal Computing (cont.)
• Gordon Bell
“The semiconductor
density has really
been the driving
force, and as you
reach different
density levels,
different machines
pop out of that in
time.”
• Would personal
computing arrive
top-down or
bottom-up?
9
Personal Computing (cont.)
• 1st mainframes operated as
personal computers
• LINC; MIT & Lincoln Labs
–1962, DEC
–Late 1960’s – 1,200 in use
• Personal tool for researcher
• Small, easy to carry tapes
–LINC + PDP-8 for $43,000
10
Calculators
• Chip density made electronic
calculators feasible & affordable
• Early ones: +,-,*,/, square root
–Too big to carry, very expensive
• 1964-Wang 300-undercut price
• HP-9100A- $5,000
• Olivetti- Programma 101- $3,500
• Still used discrete circuits, tubes,
cards (magnetic)
• 1970’s – began to use ICs
11
Calculators of 1970’s
• IC’s; $400+; size of paperback
• 1971- Bowmar Brain - $250
–1st real public notice
• Prices dropped
–1972- $150
–1973- $100
–1976- $50
• HP35 - $400- scientific, engineering
12
Calculator Trends
• Became “throw-away” items
• HP & TI survived
–HP – engineering & scientific
–TI – cut prices
• HP-65 – programmable
–Marketing - “personal computer”
13
Impact of Calculators
• Long production run
– Allowed companies to amortize high
design costs
• Unleashed personal creativity of
masses
– Hacker culture but professionals
– Users groups, etc. for support
• Chips were too specialized for
general purpose computing
14
People
• Hackers
–Did impact industry
–Serious Users had money
–Altair Kit
• User Groups
–Homebrew Computer Club-Stanford
–Tech Model Railroad Club
15
Moore’s Law
• 1964- Gordon Moore
–Fairchild  formed INTEL
–Since 1958, number of circuits on
a single integrated circuit have
doubled each year
–Predicted: by mid-1970’s would
have single chip equivalent to
1950’s mainframe
16
Computer on a chip???
• Late 1960’s; TTL & MOS (metal
oxide semiconductor)
–More density
• TI, Intel, and others
–Generally believed “computer on a
chip” was feasible, but market too
low to be profitable
• 1971 - Silicon chip
–TI, Intel
17
Invention of Microprocessor
• Intel - Focus on memory, not
logic chips
• Busicom, Japan, Calculator Co.
– Wanted set of custom logic chips for
line of specialized calculators
• Ted Hoff- assigned
– Inspired by PDP-8
– Design few general purpose chips &
tailor with software
18
Hoff’s Logic Chip
• All components of general-purpose
computer
• Patent Diagram Pg. 219
• Critical feature: subroutine call
–Used stack for multiple calls
• Slow; but plenty fast for calculator
• Complexity in the software in memory
–Recall Maurice Wilkes
19
Intel’s Microprocessor
• R. Noyce: Negotiated lower price to
Busicon for rights to sell chips to
non-calculator customers
• 1971- set of 4 chips
– “A micro-programmable computer on a
chip”
– 4004:registers & control function
– ROM (EPROM)
– RAM
– Chip for output
20
Intel 4004-8008-8080
• 4004; 1971
– Worked with groups of 4 bits
– Much question over patents (2)
• 8008; 1972
– For Computer Terminal Corp (later Data
Point), San Antonio – for terminals
• Chose another chip
– Worked with 8-bit byte
• Others now offering processor chips
21
Intel (cont.)
• 8080; 1974
–More memory
•near compatibility of mini
–Less support chips
–$360 (?Why?)
–Compatible with 8008
–Instruction set, memory range
similar to current minicomputers22
Intel’s Early Chips
Intel’s 4004, 8008, 8080 Chips
23
Early 1974 Climate
• Semiconductor engineers 
powerful microprocessors +
larger memories
• Time-sharing users
* Did not see the convergence
coming
24
MICRAL-1973
• 1st micro-processor-based
computer sold commercially
• Thi Truong- France
• Based on 8008
• < $2,000; 2000 sold
• Replaced mini’s for control systems
• Never expanded market
25
Intel Development System
• Kit: RAM, ROM, + control on a
circuit board
–Tutorial
– $200 or free
• Industrial customers developed
applications & burned on ROM Embedded Controller
26
Intel System (cont.)
• Intellec 4 & 8 (pg. 223)
–$10,000
–Develop software- PL/M, FORTRAN
• PL/M compiler resident
–Were PC’s, but not recognized
–Not available to public
–“public wouldn’t want to do
programming”
27
Hobbyists Get Involved
• There were hobbyists who were willing
to micro-program
• After WWII- Electronics hobbies grew
– Expertise and war surplus
• Electronics magazines
– QST; Popular Electronics, Radio Electronics
– Typically included a project
• Could purchase parts
28
Kenbak-1
• Scientific American
–Sept. 1971
–For private use & schools
• Small & medium scale IC’s
• No Microprocessor
• Very limited capabilities
29
Scelbi - 8H
•March 1974 QST
•Intel 8008
–1st microprocessor
sold to public
• Kits as low as
$440
30
Mark -8
• Radio- Electronics
– July 1974
• Intel 8008
• Had to order $5.00 booklet
– Sold thousands
• Mark-8 Users Group, Denver
– Stored programs on audio cassette
• Set of circuit boards - $47
• 8008- $120
31
TV-Typewriter
• Radio-Electronics, Sept. 1973
• Displayed alphanumeric
characters on ordinary TV
–ASCII based
• First “Screen” (vs. teletype)
• “the opening shot of the
computer revolution”
32
1974- Personal Computing
• January: HP-65 Programmable
Calculator
• Summer: Intel 8080
• July: Radio- Electronics, Mark 8
• December: Jan. issue of Popular
Electronics
• Altair- $400
33
MITS Altair
• Edward Roberts – Designer
– “Invented Personal Computer”
– Small hobby shop, Albuquerque
• 1st Personal Computer- “minicomputer
kit”
• 8080 Micro-processor; IC’s; TTL
• Why Success??
– Promoted & designed as minicomputer
– Powerful as commercial mini
34
Altair 8800 (cont’d)
• Modeled after D.G.
Nova
• IC memory
• 1/10 cost of mini- $400
• Cost of 8080; Not
$360 but $75
– Faster than Scelbi & Mark 8
35
Altair (Cont.)
Open Bus
• Replaced cable after
1st model lost
• Circuit boards + 2
cards
• Also, company
• Many slots
couldn’t keep up with
• Released specs so
orders
others made cards
• Several years to
• But, opened door for
peripherals/
improvements, clones
applications
36
1975-1977
• Burst of Creative Energy
• User groups, newsletters, clubs,
magazines, conventions, retail stores
• Cassette storage; “Kansas City
Standard” (from user group)
• Lack of peripherals, storage held
back the development
• ROADBLOCKS:
– No Mass Storage Device
– No way to write applicatons
37
BASIC
• No OS, No programming languages for P.C.
• Current BASICs not acceptable
– Versions; try to fit to small computers
• Altair announcement
– Bill Gates / Paul Allen decided to write
BASIC compiler for Altair
– Better - available in June 1975
•Use ONLY 4K of memory
•New version soon
38
BASIC Cont.
• Cost with Altair memory boards
–$60 for 4K; $75 for 8K
–$150 for extended (needed
storage)
• $500 for other 8080 systems
• USR – convert to machine language
• Other extensions – Peek, Poke
39
Development of BASIC
• Gates @ HARVARD; no 8080
system
• With Monte Davidoff
• Wrote PDP-10 using 8080
specification
• 1975- Paul Allen demonstrated
in Albuquerque to Roberts and
Yates
• Altair began to advertise
40
Open Letter to Hobbyists
• Bill Gates
• Problems with illegal copies of BASIC
• “The value of the computer time we
have used exceeds $40,000.”
• If not paid there will be no incentive
to develop future software, putting
personal computing at risk
• Microsoft moved from N.M. to
Bellevue, WA - 1978
41
Floppy DISK
• David Noble, IBM
– For 370 initial control program (no core)
– Didn’t expand to other uses
• Gary Kildall- consultant to Intel
developing languages
– Noted floppy
– Wrote a small program to manage
information to & from floppy
• Fast; Random access; read and write
42
“Small” Operating Systems
• DEC tape still heavily used on
PDP’s
• Late 1960’s- DEC OS/8 for PDP-8
–Showed small machines could have
capabilities of mainframes
• RT-11 for PDP-11- 1974
–Managed data on disks
43
CP/M - Control Program for
Micros
• Gary Kildall (PL/M for 8080 @ IBM)
• CP/M (Control Program for Micros) - $100
– To control disk drives
– Similar to DEC commands
– $800 with floppy drive & controller
• Final piece of puzzle for PC
• Formed (Intergalactic) Digital Research
–Product CP/M
44
Micros (cont.)
• IMSAI- Altair clone
–Wanted CP/M license
–Redesigned CP/M so small
portion customized for IMSAI
–Specialized Part BIOS
•BASIC Input/ Output System
•This Standardized system sw
45
1977
• All parts in place for PC
revolution
• Altair + add-ons
• MS Basic + SW for $$
• 8 inch floppy + CP/M
• Ports for peripherals
• Lots of publications &
groups
46
Chapter 7
1972 - 1977
The Personal
Computer
47