There are two categories of cache memory: Internal and External.
In older CPUs, and even in some current CPUs, Internal cache is memory located
in the CPU, and external is located on the motherboard between the RAM and the CPU.
It is often called 'cache RAM'. Internal Cache memory is often called "level 1"
or L1 cache. External cache is often called "level 2" or L2 cache. L2 Cache
may be on-board (in the CPU chip) or in Static RAM (SRAM) chips on the motherboard.
L2 Cache RAM is a small block of high-speed memory, usually SRAM (Static RAM),
located between the CPU and main memory. It is used to store data or instructions
that are used often. It also has the quickest access for memory for the CPU. There
are several types of SRAM with the fastest having a speed of 4-8 ns.
External cache acts as a quick access buffer between the RAM and L1 cache in the CPU.
From experience, external cache is a type of buffer for for data movement
between devices such as disks, or CD-ROM. Our experience with a 486DX with "external" cache versus one
with no external cache is this: The two were started reading 31MB of data
from a CD-ROM over the network. The one with external cache finished the
job in half the time of the one without external cache.
Internal Cache memory usually runs from about 1KB (1024 bytes) to 64KB.
External Cache memory usually runs from 64KB to 1 MB. Internal cache
normally cannot be upgraded; however, external cache can often be upgraded.
External cache is normally a plug device - it plugs into "cache" sockets
located on motherboards, and even on individual boards such as Network Interface
Cards, video cards, etc.
NOW: In the newer processors, such as Pentium Pro and Pentium II, you
will see new designations for cache. Some will have L1 cache (internal cache)
and L2 cache (what used to be external cache). The Pentium II processor claims
to have 512KB of integrated L2 cache.
These machines have both types of cache integrated into the microprocessor.
This is a serious improvement - it gets the external cache, or L2, off the motherboard,
and puts it where the cache can run at the full CPU speed rather than at
the slower motherboard speed. A new designation "L3" will be used for
cache that is on the motherboard.
When you boot your PC, you usually see a display of memory which shows
Conventional and Extended memory, as well as the types and amounts of cache.
I would recommend you purchase a PC with at least 256 KB of cache - if you
can afford it. The first 256K of cache saves the computer lots of time, but
adding more does not improve performance proportionally.
For a complete discussion of all types of memory, I suggest you go to
"www.kingston.com", or "www.centon.com" on the WEB.
Memory Menu