wow wow
Such great info
Thanks for this tehrhrhrhrhrhrhrific description!
Keep Smiling,
Janie Degenshein
"Happiness isn't having what you want, but wanting what you already have"
Access Tech Consultant
Facilitator of ECHO
(Eyes Closed Hearts Open)
President, National Federation of the Blind of New Jersey Senior Division
Co-host of OTBS On The Bright Side
www.thruoureyes.org/brightside.html
jdege...@comcast.net
-----Original Message-----
From: David Ferrin
Sent: Tuesday, January 17, 2012 10:31 AM
To: jaws-users-list@jaws-users.com
Subject: [JAWS-Users] daily information
Daily Tip:
Excel: Change Decimal Places (Worksheet)
To change the decimal places in cells, select them and then click the Home
tab, if it isn't already selected. Click the Increase Decimal or Decrease
Decimal icons.
Daily Term:
cache
The cache memory areas on and near your microprocessor are a vital component
for giving the microprocessor improved speed and performance. The cache
(pronounced "cash") provides high-speed, temporary data storage areas the
microprocessor can access quickly. You can think of the cache area as a
high-speed memory subsystem for your computer.
Cache memory areas are able to improve the performance speed of a
microprocessor through four means. First, the cache memory consists of
memory technology that works more quickly than the traditional RAM in your
computer; it's also far more expensive. (Cache memory typically consists of
SRAM [static RAM] versus the DRAM [dynamic RAM] usually used as the
computer's main RAM.) Second, the cache memory areas are much closer to the
microprocessor than traditional RAM, meaning they can deliver the data more
quickly. Third, most cache areas run at nearly the same clock speed as the
microprocessor, letting them work more closely in tandem. RAM runs at a much
slower clock speed than the microprocessor. Finally, because the
microprocessor typically only uses a small portion of a program or a data
file at a time, storing the commonly used portion in cache is useful, even
if the original program or data file is far too large to fit entirely in
cache.
Today's microprocessors make use of two cache areas: L1 (level 1) and L2
(level 2). L1 cache is also known as on-die cache, on-chip cache, and
primary cache. L1 cache usually sits directly on the microprocessor and is a
smaller memory area than L2 cache. L1 cache is the first area the
microprocessor checks when looking for data stored in memory. The L2 cache
usually resides on the motherboard, although some manufacturers include L2
cache as part of the microprocessor's packaging or on the microprocessor
itself, and is the second area the microprocessor checks for data stored in
memory. To improve the performance of the L2 cache, microprocessor
manufacturers a few years ago began connecting the microprocessor and the L2
cache with a backside bus. The microprocessor checks both cache areas before
checking RAM. When the microprocessor finds the data it wants in the cache
areas, it's called a cache hit. If the cache doesn't have the needed data,
it's called a cache miss. As the microprocessor's data needs change, it
updates the data it stores in the L1 and L2 caches, overwriting the oldest
data in the caches.
In newer microprocessors, such as the Pentium 4 from Intel, the
microprocessor uses prediction technology to determine the best sets of data
to place in the L1 and L2 caches. This prediction technology is important to
overall performance because it increases cache hits and minimizes the amount
of time the microprocessor must wait for memory searches.
Cache memory first appeared in a computer-the IBM System/360 Model 85-in
1968. Nearly every PC built since then has included some type of cache
memory. The Intel 468DX microprocessor, which Intel introduced in 1989,
featured L1 cache on the chip for the first time, but it only had 8KB of
cache memory. Off-chip L2 cache areas appeared soon after with 486DX4 and
Pentium microprocessor chips from Intel in the early 1990s. Intel's Pentium
II microprocessor, introduced in 1997, was part of an SEC (Single Edge
Contact) Cartridge that included a high-speed cache memory chip. Today's
microprocessors usually have 128KB or more of L1 cache memory and 256KB or
more of L2 cache memory.
Because of the expense of cache memory, some low-price computers from a few
years ago might be missing the L2 cache on the motherboard or
microprocessor. Intel's initial Celeron processor, for example, didn't
include L2 cache. However, as microprocessor components have continued to
shrink and memory components have continued to be less expensive, almost all
recent and current microprocessors contain L2 cache. With microprocessor
components continuing to shrink, nearly all future microprocessors probably
will contain an on-chip L2 cache. Newer Athlon microprocessors from AMD
(Advanced Micro Devices), for example, include the L2 cache on the chip,
improving its performance by about 300%. Some industry analysts think that
as on-chip L2 caches become commonplace, computer manufacturers will begin
including an L3 cache on the motherboard.
Terms associated with cache:
cache buffer: A cache buffer is the area of RAM (usually 2MB or less in a
PC) that exists within nearly all newer hard drives, CD-RW (CD-rewriteable)
drives, and DVD-ROM drives, giving the microprocessor faster access to data
that's normally in permanent storage. The cache buffer usually maintains a
copy of the latest data the microprocessor retrieved from permanent storage.
In most newer printers, manufacturers have included cache buffers, which
hold data waiting to be printed. A similar process, called disk caching,
reserves a portion of RAM to mirror the last data from the hard drive,
giving the microprocessor faster access to the data if it's needed again.
Web browser cache: Cache also refers to the portion of memory and the
computer's hard disk that Web browsers use to store temporary Internet
files, usually called the Web browser cache. Using a portion of the
computer's resources to store Internet files, especially graphical images,
lets the Web browser display Web pages more quickly than it could by
downloading the graphics from the Internet. Using a cache area makes sense
in this instance because the graphics on a Web page rarely change.
cache servers: ISPs (Internet service providers) and Internet content
providers also make use of cache servers (sometimes called cache
appliances), which are specialized computers that store copies of commonly
accessed Web pages. Cache servers usually use software to measure the most
popular Web pages and then download those pages to the cache server during
nonpeak Internet usage times. The cache servers then check back with the
originating Web server from time to time to look for changes and updates.
Cache servers are located throughout the world, and they help speed
downloading of Web pages by two methods. First, they alleviate traffic on
the server where the commonly accessed Web page resides, giving the server
better overall performance. Second, because chances are good one of the
cache servers is physically closer to your computer than the originating
server is, the Web page has a shorter distance to travel to your computer
and can arrive faster.
David Ferrin
"Too many people spend money they haven't earned to buy things they don't
want to impress people they don't like"
Will Rogers
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