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
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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.
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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?
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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 www.newegg.com (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.
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Caches
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
discovered)
An average access time of 14 ns compared to an access time of 40ns
without the cache--about three times as fast!