The 8086 family and some other hardware. (january 2008)

year:  year introduced.  data bus:  size of the data bus.  addr bus:  size of the address bus.  max mem: max amount of memory
typical memory:  typical amount.  clock speed:  mhz = megahertz  ghz = gigahertz
name        year     data bus  addr bus   max mem   typical memory   clock speed        other
8086         1978      16              20             1 meg           500k-1meg         5-10mhz           first IBM PCs:  64K ram, $4000
8088         1979        8              20                "                        "                      "                      simplified, cheaper 8086 (and slower)
80186       1982      16              16?              "?                        ?                 6-12 mhz          embedded systems--not really for PCs
80286       1982      16              24              16meg         1 meg?                 6-13 mhz
80386       1987      32              32              4 gig            16 meg                16-40mhz      mainstay.  external cache, ect
80486       1989      32              32                 "               16 meg?              16-133mhz    8K on-chip cache, 2 ALUs
Pentium  1993      64              32                lots               2 gig +              60mhz-3.6 ghz  multiple ALUs, many configs

Auxilliary Memory
cassette tape       1972?    64K??  very old medium for Apples, etc.
8" floppy           1972    360K storage.  bulky, obsolete
5 1/4" floppy     1978    360K storage.   long a mainstay, but picked up dirt and mildew, not rugged.
3 1/2" "floppy" 1984   720K storage.  not actually floppy, rugged, longer lasting
3 1/2" various       extra storage.  high-density drives could read both HD and normal disks
CD                                  700M  used for audio, etc, before widespread use for PCs
DVD                               4.7-8.5Gig.  DVD drives for PCs also read CDs
zip drives, etc    basically external hard drives for backups, transfers, etc.
flash drives        for USB ports.  cheap, hold 2 gig and up storage.

Notes of interest.
People with 3 1/2" floppy drives who wanted to install LINUX on their PCs needed to be patient.  LINUX came on
about 50-60 3 1/2" floppies--you had to install the software in the correct order from each floppy disk, and hope that
you didn't have a power failure during the process.  The old 8" floppies were bulky (imagine trying to fit one in your
shirt pocket).  5 1/4" disks were cheap and common--and were flexible (you could bend and twist them).  But the disks
themselves were not well protected--dirt got in easily, as did mildew and bugs, so you made backups often.  The 5 1/4"
drives provided nice openings for dirt and dust--their life expectancy was not great.   3 1/2" disks were a great step
forward:  the disk itself had a sliding cover that normally opened only when you put the disk in the drive, and the drive
had a flap that helped keep out dirt.  But as time passed, games and other software grew in size, so you might buy a game
that came with 8 3 1/2" disks--not too convenient.  CDs held 1000 times the storage of a 3 1/2" disk--but most people
didn't want to get a CD writer for their PC.  5 1/4" and 3 1/2" disks could easily be written to as well as read from--
but most people mostly just wanted to read, and so the CDs were fine, as are the DVDs.  If you want to transfer data,
the internet is easy, and flash drives are also a very cheap and easy way to back up storage and transfer data.  Lots of
people go to conferences without bothering to take along their laptops--they just carry everything they need on a flash
drive and borrow a machine when they arrive. 

The Encyclopedia Britannica--32 volumes, 36K pages, $1600+--not too portable.  Available also on DVD, $40.  Why?

Hard Drives.
The original IMB PC--$4000.  64K of memory, black and white monitor, no hard drive.  Within a year or so IBM had
an updated version--new motherboard--that could handle a hard drive (the original made no provision for a hard
drive).  Original IBM hard drive--$4500 for a 10mb hard drive.  So--$8500 for a PC with a hard drive.  On a personal
note--my first hard drive cost $450, and was a 40mb drive on a plug-in card for my 8088-based PC.  When I upgraded
to an 80386 my hard drive was 156mb (and weighed about 15 lbs just for the drive--like carrying a bowling ball inside
my PC).  Luckily, drives have gotten cheaper--much cheaper.  Visit (or any similar place):  you can
get a 750gb hard drive for $199--this is almost 20,000 times the storage of my first hard drive at less than half the cost,
and this doesn't take inflation into account.
There are probably about 5-10 caches of different kinds in your PC.  Caches are designed to speed up memory access
and to improve computing throughput.  You'll have caches on your CPU, probably on your hard drive, etc.  To show
how they work, let's assume that you have an external cache (i.e. between the CPU and main memory) with a 90% hit
rate and a 10ns access time.  A 90% hit rate means that 90% of the time the desired data is in the cache--10% of the
time you have to keep going to slower-access memory (not necessarily main memory--a cache miss for an L1 cache
means that the L2 cache comes next).  Let's also assume that main memory has a 40ns access time.  So:
1) 90% of the time, the access time will be 10ns.
2) 10% of the time, after taking 10 ns to check the cache, the desired data isn't there--so we need to go to main memory--
another 40 ns (50ns total).
average access time = .90  x  10ns + .10 x (10ns + 40ns) = 9ns + 5ns = 14ns. (the 10ns in the latter part is for the cache miss to be
An average access time of 14 ns compared to an access time of 40ns without the cache--about three times as fast!